Technical Field

The invention relates to a method for determining a characteristic value of an optical system, an optical measurement device, an evaluation device, a computer program, a computer-readable storage medium and a use of a sample for performing a method for determining a characteristic value of an optical system. Such optical measurement device may, in general, be employed for investigation or monitoring purposes.

Background art

Optical metrology systems, typically, enable reliable, fast, and non-invasive measurements for a large range of applications, including, but not limited to, imaging, microscopy, distance measurement, spectroscopy, astronomy, each, generally, in a plurality of variations and implementations.

Specifically in diffusive reflective spectroscopy strongly granular samples may be measured. Such granular samples may be known from agricultural applications and may include, but are not limited to, grains and/or soils. Further such granular samples may be known from material classification applications including, but not limited to, plastics sorting or classification of fabrics. However, further kinds of applications are possible.

In these measurements, typically, optical signal generated by at least a portion of a sample may be evaluated for determining a desired result. The desired result may be an information about the sample. In a scenario in which granular samples are measured, a size of a measurement spot of a field of view of a measurement device and the optical resolution of the optical measurement device may be of particular interest and is, generally, required to be well characterized, particularly as granular samples may generate fluctuating measured optical signal, when the size of the measurement spot field may compare to a spatial granularity in the sample of view may, thus, may allow collecting information on the granularity of the measured sample. For a large field of view, when the spot size may be larger than the typical system length scales of the sample, the spatial granularity in the sample, generally, averages out and the measured optical signals may not be influenced by the granularity.

International standard for characterization of laser beam parameters ISO 11146-1 :2005(en), Lasers and laser-related equipment — Test methods for laser beam widths, divergence angles and beam propagation ratios — Part 1: Stigmatic and simple astigmatic beams, describes especially in ISO/TR 11146-3, three alternative methods for beam width measurement and their correlation with the method used in this part of ISO 11146, wherein the methods are a variable aperture method, a moving knife-edge method, and a moving slit method.

Mohamed Sadek, Shady Labib, Bassem Mortada, Mostafa Medhat, Tarek Zeinah, Ahmed Shebl, Ahmed Fadeel, Mina Gad, Hussien Abuelnaga, Botros George, Yasser Sabry, Bassam Saadany, Large spot size diffuse reflectance FT-NiR spectral sensor for inhomogeneous samples, SPIE Optical Metrology, 21-26 June 2021 , Proceedings Vol. 11782, present that diffuse reflectance infrared spectroscopy has gained traction in many industrial applications in the recent years due to the emergence of new generation of low cost handheld spectrometers that did not exist a decade ago. Real-time monitoring puts a limit on the sample preparation process especially with inhomogeneous samples in the food industry, like grains, hay, wheat and corn. The heterogeneity of the samples and the pseudo-random spatial arrangement of the grains in front of the optical interface, leads to prediction errors. The spatial variations depend also on the spot size of the diffuse-refl ected scattered light from the sample that is collected by the spectrometer. A larger spot size leads to simultaneous averaging of a larger amount of spectrospatial information from different locations on the sample, leading to better repeatability and better prediction accuracy. Up to date, the Microelectromechanical (MEMS) based spectrometers reported in the literature have limited optical spot size, usually smaller than 3 mm in diameter. They reported MEMS based FTIR spectral sensors with optical spot sizes of 6 mm, 10 mm and 20 mm working across the spectral range of 1350 nm to 2500 nm. The core spectral engine comprises monolithic MEMS chip, micro-optics for light coupling and a single photodetector in a tiny package. The optical head combines several miniaturized filamentbased lamps and reflective optics for illumination. The sensors are compared and the 10-mm sensor gives an optimal performance with a Signal to Noise Ratio (SNR) of 4000:1 and spectrospatial photometric repeatability down to 0.02 absorbance units.

Faulhaber Andreas et aL, Dynamic holography for speckle noise reduction in hybrid measurement system, PROCEEDINGS OF SPIE, vol. 10744, 14 September 2018, pages 107440J-107440J, describes measurement systems for metrology incorporating lasertriangulation methods have the problem of speckle noise. This noise is an effect of the coherence of the laser light in combination with the projection onto rough object surfaces. They show results for using spatial light modulators within a simple and effective method in order to reduce the speckle noise in laser-based triangulation.

Mohammed Belal Hossain Bhuian, Development of a Laser Based Inspection System for Surface Defect Detection, School of Mechanical & Manufacturing Engineering, City Dublin University, April 2002 (2002-04), pages 1-165, describes design and develop of a laser based inspection system for detection of surface defects and assess its potentiality for high-speed online applications.

US 2015/036142 A1 provides various metrology systems and methods. One metrology system includes a light source configured to produce a diffraction-limited light beam, an apodizer configured to shape the light beam in the entrance pupil of illumination optics, and optical elements configured to direct the diffraction-limited light beam from the apodizer to an illumination spot on a grating target on a wafer and to collect scattered light from the grating target. The metrology system further includes a field stop and a detector configured to detect the scattered light that passes through the field stop. In addition, the metrology system includes a computer system configured to determine a characteristic of the grating target using output of the detector. Franceso de Angelis et aL, Nanoscale chemical mapping using threedimensional adiabatic compression of surface plasmon polaritons, NATURE NANOTECHNOLOGY, vol. 5, no. 1, 22 November 2009, pages 67-72, describes that the fields of plasmonics, Raman spectroscopy and atomic force microscopy have recently undergone considerable development, but independently of one another. By combining these techniques, a range of complementary information could be simultaneously obtained at a single molecule level. They report the design, fabrication and application of a photonic-plasmonic device that is fully compatible with atomic force microscopy and Raman spectroscopy.

US 2012/008143 A1 discloses the determination of particle sizes. In particular, the determination of the sizes of particles in a particle stream. For this purpose, a first optical measuring system having a first matrix sensor and a lighting means which lights up the measurement volume are provided, wherein the first matrix sensor and the lighting means form a transmitted-light arrangement, and wherein the computation device is set up to use the image data from the first matrix sensor to determine projection surfaces of particles inside the measurement volume which has been lit up, and wherein the optical measuring arrangement comprises a second optical measuring system having a second matrix sensor for detecting the diffraction pattern of the particle, and wherein the computation device is set up to use the projection surfaces and the diffraction pattern to determine a size distribution of the particle in the measurement volume, wherein the computation device is set up to form the size distribution from particle sizes determined using the projection surfaces and from particle sizes determined using the diffraction pattern.

WO 2022/064147 A1 discloses a method of analyzing a biological sample comprising biological agents and disposed in an analysis receptacle in a field of view of a holographic imaging system defining an acquisition focal plane, comprising, or each of a plurality of measurement times: acquiring a plurality of holographic images of the biological sample at different respective positions of the acquisition focal plane, and, from each acquired holographic image, determining a value of a biomass parameter representative of the quantity of biological agents at the position of the acquisition focal plane, the method comprising constructing a distribution indicator from values of the biomass parameter at the same measurement time for a plurality of positions of the acquisition focal plane, and providing, among the analysis results, a representation of the distribution of the biomass of biological agents, derived from at least one distribution indicator at a measurement time.

EP 3 584 564 A1 discloses an electromagnetic wave detecting device comprising: an emission unit configured to emit electromagnetic waves having coherence; an electromagnetic wave modulating unit configured to modulate one or both of a phase and an amplitude of the emitted electromagnetic waves and to change a state of the modulation relative to an imaging target; and a post-modulation electromagnetic wave intensity detecting unit configured to detect an intensity of post-modulation electromagnetic waves, which are the modulated electromagnetic waves acquired by modulating the electromagnetic waves emitted from the emission unit using the imaging target and the electromagnetic wave modulating unit, using one pixel. Despite the advantages achieved by known methods and devices as discussed above, several technical challenges remain. Specifically, the characterization of the optical system may still be challenging.

Problem to be solved

It is therefore desirable to provide a method for determining a characteristic value of an optical system, an optical measurement device, an evaluation device, a computer program, a computer-readable storage medium and a use of a sample for performing a method for determining a characteristic value of an optical system, which at least partially overcome the problems of the state of the art.

It is further desirable to provide a method for determining a characteristic value of an optical system, an optical measurement device, an evaluation device, a computer program, a computer-readable storage medium and a use of a sample for performing a method for determining a characteristic value of an optical system which allow a reliable, fast and efficient characterization of an optical system and an optical measurement device.

Summary

This problem is solved by a method for determining a characteristic value of an optical system, an optical measurement device, an evaluation device, a computer program, a computer- readable storage medium and a use of a sample for performing a method for determining a characteristic value of an optical system having the features of the independent claims. Advantageous embodiments which might be implemented in an isolated fashion or in any arbitrary combinations are listed in the dependent claims as well as throughout the specification.

In a first aspect of the present invention, a method for determining a characteristic value of an optical system is disclosed, wherein the optical system comprises a sample and an optical measurement device, wherein the optical measurement device is configured for measuring a plurality of optical signals generated from different portions of the sample.

The method for determining a characteristic value of an optical system comprises the following steps, which may be performed in the given order. A different order, however, is also feasible. Further, two or more of the method steps may be performed simultaneously or in a fashion overlapping in time. Further, the method steps may be performed once or repeatedly. Thus, one or more or even all of the method steps may be performed once or repeatedly. The method may comprise additional method steps which are not listed herein.

The method comprises the following steps:

(i) providing data comprising information about a plurality of optical signals, wherein each optical signal is generated by at least one channel of the optical measurement device using incident radiation generated from a portion of the sample, wherein at least two of the optical signals are recorded from different portions of the sample by directing at least one measurement spot of the field of view of the optical measurement device to the different portions of the sample, wherein the sample comprises at least one pattern having at least one characteristic extension, wherein the at least two of the optical signals depend on the at least one characteristic extension of the pattern and on a size of the at least one measurement spot directed to the different portions of the sample;

(ii) determining a characteristic value of the optical system by evaluating a degree of variation of the plurality of optical signals.

The term “characteristic value” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a parameter comprising information about the optical system, specifically about at least one of the sample, or the measurement device. The information may describe the nature of the optical system, specifically of at least one of: the sample; or the measurement device. The information may be a defining feature of the optical system. Possible characteristic values will be described in more detail below. However, there may be further characteristic values that may be determined.

The term “optical system” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an entity that may consist of at least two or a plurality of components, particularly wherein the components may have at least one different property. The components may be regarded as a common whole due to their interaction via radiation.

The term “sample” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to the entirety of the medium to be examined. The sample may be a granular sample, specifically wherein the granular sample comprises at least one of: grains; milled seeds; silage; shredded plastics; or food. Thereby, the sample may be a mixture of separable constituents. The constituents may generate a pattern, particularly may be considered as at least one feature of a pattern. Alternatively or in addition, the sample may have an internal structure, particularly wherein the sample is selected from at least one of wood, concrete, or sausage. The internal structure may generate a pattern, particularly may be considered as at least one feature of a pattern. Alternatively or in addition, the sample may be a carrier for an artificially generated, particularly printed or displayed, pattern.

Radiation, specifically electromagnetic radiation, more specifically light, emerging from the sample may originate in the sample, specifically in the pattern, itself, but may also, optionally, have a different origin and propagate from this origin to the sample, specifically the pattern, and subsequently towards the optical measurement device. The latter case may, in particular, be affected by at least one illumination source being used. Thus, the radiation propagating from the object to the optical measurement device may be radiation which may be reflected by the sample. Alternatively or in addition, the radiation may at least partially transmit or propagate through the object. Alternatively or in addition, the pattern may be generated by at least one illumination source, specifically a LED or a laser. Alternatively or in addition, the pattern may be generated by a screen, specifically a LCD screen or a LED screen. Alternatively or in addition, the pattern may be generated by a spatial light modulating element, specifically a LCD or a micro mirror array. Alternatively or in addition, the sample may be the illumination source, the screen and/or the spatial modulating element. Alternatively or in addition, the sample may reflect and/or transmit the pattern generated by the illumination source, the screen and/or the spatial modulating element.

The term “optical measurement device” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an instrument for detecting qualitatively or quantitatively a radiation, specifically an electromagnetic radiation, more specifically light. The radiation that may be detected by the optical measurement device may emerge from the sample. The detected radiation may generate optical signals that are measured by the optical measurement device. The optical signals may be provided by the optical measurement device for further evaluation, specifically by an evaluation device, particularly for determining a characteristic value of the optical signal.

The term “plurality of optical signals generated from different portions of the sample” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to detecting a plurality of optical signals emerging from different portions of the sample. The term “optical signal” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a piece of information about radiation. The radiation may be radiation that is incident into the optical measurement device, particularly incident radiation that is detected by the optical measurement device. The radiation may emerge from the sample, specifically the pattern of the sample, more specifically the at least one extension. An optical signal may comprise information about a portion of the sample. During generating the optical signal the optical measurement device may be directed at the portion of the sample, particularly the measurement spot may remain at the portion of the sample. Alternatively or in addition, during generating the optical signal, the measurement may not be directed at a different portion of the sample. The optical signal may be generated, specifically exclusively, by a property of the incident radiation selected from at least one of: the identical optical property is selected from at least one of an intensity, a polarization, a spectral flux, an irradiance, a radiance, an optical flux.

According to step (i), data is provided comprising information about a plurality of optical signals, wherein each optical signal is generated by at least one channel of the optical measurement device using incident radiation generated from a portion of the sample, wherein at least two of the optical signals are recorded from different portions of the sample by directing at least one measurement spot of the field of view of the optical measurement device to the different portions of the sample, wherein the sample comprises at least one pattern having at least one characteristic extension, wherein the at least two of the optical signals depend on the at least one characteristic extension of the pattern and on a size of the at least one measurement spot directed to the different portions of the sample.

The term “data” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an item, such as a numeric item, which comprises at least one piece of information. The term “information” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a content being comprised by the piece of data. The information may be the plurality of optical signals that are provided for the method to be evaluated, particularly including the information about the plurality of the optical signals being relevant for the determination of the characteristic value of the optical system. Alternatively or in addition, the information about the plurality of the optical signals may comprise for each optical signal of the plurality of optical signals the detected property of the incident radiation and/or the intensity.

The term “channel of the optical measurement device” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a generator of at least a portion of an optical signal. Each channel of an optical measurement device may comprise an individual field of view. Typically, when an optical measurement device comprises one channel, the optical signal may be generated by the one signal. Further typically, when an optical measurement device comprises a plurality of channels, the plurality of optical signals may be generated by the plurality of channels, particularly thereby a portion of the optical signal may be generated by a channel and at least one further portion of the optical signal may be generated by at least one further channel. The portion of the optical signal and the further portion of the optical signal may be different. For determining the characteristic value of the optical system, particularly related to one specific channel, only the portion of the plurality of optical signals generated by this channel may be considered.

The term “radiation” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to waves and/or particles that carry energy. The radiation may be electromagnetic radiation. Electromagnetic radiation may be formed by at least one electromagnetic field wave. The electromagnetic radiation may be selected from at least one of: radio waves; microwaves; infrared; visible light; ultraviolet; X-rays; or gamma rays. Specifically, the electromagnetic radiation may be light. Light may be electromagnetic radiation that may be perceivable by the human eye. Visible light may, usually, be defined as having wavelengths in the range of 400 - 700 nanometers, between the infrared and the ultraviolet. The term “field of view” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an extent of the observable world that is observable. The field of view of the optical measurement device may be the extent of the observable world in which the optical measurement device may be sensitive to the radiation. Radiation generated within the field of view may be accepted by the optical measuring device and measured by the optical measuring device.

The term “measurement spot” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a surface generated by the field of view that is located on the portion of sample from which radiation may be measured by the optical measurement device.

The term “directing at least one measurement spot of the field of view of the optical measurement device to the different portions of the sample” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to measuring a plurality of optical signals emerging from different portions of the sample. Typically, a portion of the sample may be measured by directing a measurement spot of the field of view of the optical measurement device on this portion of the sample. For measuring a plurality of optical signals generated from different portions of the sample, the measurement spot may be directed to a first portion for measuring a first optical signal and, particularly subsequently, the measurement spot may be directed to a second portion for measuring a second optical signal, wherein the first portion and the second portion are different portions. Particularly further subsequently, the measurement spot may be directed to at least one further portion for measuring at least one further optical signal, wherein the first portion, the second portion and the at least one further portion are different portions. The portions may be different portion by being located at different spots on the sample. The optical signal generated at a portion of the sample may be generated by at least one channel of the optical measurement device, specifically the one specific channel of the optical measurement device or a plurality of channels of the optical measurement device.

The term “pattern” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a scheme, specifically a repeating schema. The pattern may comprise the at least one characteristic extension. The term “characteristic extension” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to at least one degree of at least one spatial dimensions of an object. The characteristic extension may refer to at least one feature of the pattern, particularly wherein the characteristic extension may be the size of the at least one feature. Alternatively, the characteristic extension may be the entire pattern, particularly wherein the characteristic extension may be the size of the pattern. Radiation may emerge from the characteristic extension in such a manner that the optical signal may depend on the at least one characteristic extension of the pattern.

The term “the at least two of the optical signals depend on the at least one characteristic extension of the pattern and on a size of the at least one measurement spot directed to the different portions of the sample” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to the at least two of the optical signals being influenced by the at least one characteristic extension of the pattern and on a size of the at least one measurement spot directed to the different portions of the sample. Typically, an optical signal may vary when it is measured for different sizes of the at least one measurement spot. Alternatively or in addition, an optical signal may vary when it is measured for different characteristic extensions, particularly comprised by the same sample or by different samples. The variation may be caused by the granularity of the sample, particularly when the size of the measurement spot compares to typical length scales of the granularity of the sample.

According to step (ii), a characteristic value of the optical system by evaluating a degree of variation of the plurality of optical signals is determined.

The term “determine” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a process of generating at least one representative result. The term “degree of variation” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an amount of change or fluctuation between at least two situations. The degree of variation may be determined by a statistical evaluation of at least a portion of the plurality of optical signals. The variation may be the change or fluctuation between a first optical signal and at least one further optical signal. The first optical signal may be detected by maintaining the measurement spot on a first portion of the sample. The second optical signal may be detected by maintaining the measurement spot on a second portion of the sample. The first portion may be different from the second portion. The variation may be caused by a granularity of the sample, particularly when the size of the measurement spot compares to typical length scales of the granularity of the sample.

The at least two of the optical signals may be recorded by the same at least one channel. The optical measurement device may comprise a plurality of channels and/or the at least two of the optical signals may be recorded by different channels of the plurality of channels.

The degree of variation of the plurality of optical signals may be evaluated by analyzing at least one of: a standard deviation of the plurality of the optical signals; a variance of the plurality of the optical signals; a maximum intensity optical signal of the plurality of the optical signals; a minimum intensity optical signal of the plurality of the optical signals; a difference between two optical signals of the plurality of the optical signals, particularly a difference between the maximum intensity optical signal and the minimum intensity optical signal; a distribution of the plurality of the optical signals, particularly a skewness of the distribution or a kurtosis of the distribution; or an analytical function, particularly an analytical function considering the maximum intensity optical signal of the plurality of the optical signals or the minimum intensity optical signal of the plurality of the optical signals.

The term “standard deviation” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a degree of the amount of variation or dispersion of a set of values, particularly around a mean value. It may be referred to the standard deviation as SD(S). The standard deviation SD(S) may be calculated by using the function wherein S(y) is the optical signal for N different portions at the respective center positions {y} and wherein MEAN(S) is the average of the optical signals for the N different portions.

The term “variance” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a degree of the amount of variation or dispersion of a set of values, particularly around a mean value. The variance may be the square of the standard deviation.

The term “distribution” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an analytical function that defines the probabilities of occurrence of different outcomes of an experiment. The distribution may be considered as a probability distribution.

The term “skewness” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a degree of asymmetry of a distribution.

The term “kurtosis” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a measure of a shape of a distribution.

Evaluating the degree of variation of the plurality of optical signals comprises determining an interim value by using an average of the plurality of the optical signals and the standard deviation of the plurality of the optical signals. The term “average” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a sum of a plurality of values divided by the count of the plurality of value. In may be referred to the average as MEAN(S).

The average MEAN(S) may be calculated by using the function wherein S(y) is the optical signal from N different portions having the respective center positions

The term “interim value” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a value that is determined by considering the degree of variation of the plurality of optical signals. The interim value may be proportional to the degree of variation of the plurality of optical signals, specifically the standard deviation. The interim value may be anti-proportional to the average of the plurality of the optical signals. The interim value may depend on the standard deviation and the average. The interim value may use the standard deviation and/or the average by performing a mathematical operation between them. It may be referred to the interim value as SD(S)/MEAN(S). This nomenclature does not necessarily imply that the interim value is a ratio or a quotient. The characteristic value may be determined by evaluating the interim value.

The interim value may be a ratio using the standard deviation and the average. The ratio may be determined by dividing the standard deviation divided by the average or vice versa. The interim value may be a quotient of the standard deviation divided by the average. The interim value, the ratio or the quotient may be determined by using further value, particularly for scaling. The further values may be further measured values.

The at least one pattern comprised by the sample may have a plurality of features generating the at least one characteristic extension, wherein the features generates at least one optical signal. The term “feature” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a detectable characteristic that distinguishes a thing from others. A feature may have a specific size and, alternatively or in addition, generate at least one specific optical signal. The specific optical signal may be generated, specifically exclusively, by a property of the incident radiation selected from at least one of: the identical optical property is selected from at least one of an intensity, a polarization, a spectral flux, an irradiance, a radiance, an optical flux.

Alternatively or in addition, the pattern may be arranged on a background, particularly wherein the background may be further comprised by the sample. The term “background” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a part of the sample that appears distant to an observer. The background may generate no optical signal, particularly no optical signal that may be detectable by the optical measurement device. Alternatively, the background may generate at least one further optical signal which is distinguishable from the at least one optical signal generated by the at least one characteristic extension, particularly the at least one feature. The at least one further optical signal may have at least one distinguishable optical property selected from at least one of: an intensity, a polarization, a spectral flux, an irradiance, a radiance, or an optical flux of the incident radiation. The background may generate a uniform optical signal. For a granular sample, the background may be generated by constituents comprised by the granular sample that generate no radiation or that generate radiation that is not incident into the optical measurement device.

Each feature of the plurality of the features may generate optical signals having an identical optical property, particularly with a maximum deviation of 10%, 5%; 2%, 1 % or 0.5%. The term “identical” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a similarity of a plurality of entities in at least one detail, specifically wherein the at least one details may be the optical property. The term may allow for a deviation from an exact identity, specifically a maximum deviation of 10 %, 5 %, 2 %, 1 %, or 0.5 %. The identical optical property may be selected from at least one of: an intensity; a polarization; a spectral flux; an irradiance; a radiance; or an optical flux of the incident radiation.

The characteristic value may be selected from corresponding to at least one of: the at least one measurement spot, particularly the size of the at least one measurement spot of the optical measurement device; an optical resolution of the optical measurement device; or the characteristic extension of the pattern in the sample.

The size of at least one measurement spot of the optical measurement device may be an effective size assuming a constant sensitivity to the incident radiation over the entire at least one measurement spot. The term “optical resolution” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to the ability of the optical measurement device to resolve at least one detail in the sample, specifically the pattern or at least one detail of the pattern, more specifically the characteristic extension that is being measured. The characteristic value may correspond to the characteristic extension of the pattern which may be provided by the plurality of the features, wherein the size of the plurality of the features may be a typical structure size.

The term “typical structure size” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a typical length scale provided by the plurality of the features. The typical length scale may be a correlation length of the features. In case the pattern may be a dot grid, the typical structure size may be the size of at least one dot or a plurality of dots, specifically each dot. In case the typical structure size may be the size of a plurality of dots, the size may be an average size of the plurality of dots. The size of a dot may be the radius or diameter of the dot. Alternatively or in addition, in case the pattern may be a dot grid, the typical structure size may be the distance between two neighboring dots, specifically the distance between centers of the two neighboring dots. The distance between two neighboring dots for a plurality of dots may be an average distance between two neighboring dots of the plurality of dots, specifically each dot. In case the pattern may be a speckle pattern, the typical structure size may be a correlation length related to grains comprised be the speckle pattern.

The size of the at least one measurement spot of the optical measurement device may be determined by evaluating the at least one characteristic extension of the pattern. Therefore, the at least one characteristic extension of the pattern may be known. The known at least one characteristic extension may be selected from at least one of: the size of the plurality of the features, specifically the typical structure size, more specifically a correlation length of the features; or the distribution of the plurality of the features. The term “correlation length” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a distance over which the pattern is similar to itself, particularly wherein the distance over which the emerging radiation from the pattern is similar to itself. The term “knowing” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to being available to the method, particularly in a manner of being available to be used by the method for determining the characteristic value. A known value may be used during performing the method.

A type of the pattern may be selected from at least one of: a dot grid, wherein the plurality of the features are dots comprised by the dot grid; or a speckle pattern, wherein the plurality of the features are grains comprised by the speckle pattern. However, there may be further types of patterns. The pattern may be a grey-scale pattern.

The term “dot grid” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a pattern comprising a plurality of dots, wherein the plurality of dots are the features. The pattern may be provided on a sample having a background. The background may generate no or a uniform optical signal. The plurality of the features of the dot grid may have the same size, specifically the same diameter, particularly with a maximum deviation of 10 %, 5 %, 2 %, 1 %, or 0.5%. The plurality of the features of the dot grid may have the same distance to at least one neighboring feature, specifically any neighboring feature, particularly with a maximum deviation of 10 %, 5 %, 2 %, 1 %, or 0.5%. The distance may be the distance between the centers of the dots. The term “speckle pattern” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a pattern that is, typically, produced by the mutual interference of a plurality of coherent wave fronts. The plurality of the features may be grains comprised by the speckle pattern.

The at least one characteristic extension of the pattern may be described by using a function f (x) that describes a relation between a position x of the pattern and an expected emerging radiation, wherein an autocorrelation function (y) of the function f (x) may be identical for at least two position y of the pattern or each position y of the pattern, particularly with a maximum deviation of 10 %, 5 %, 2 %, 1 %, or 0.5 %.The term “autocorrelation function” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a term from stochastics and/or signal processing describing the correlation of a function and/or signal with itself at an earlier point in time and/or at a different position. The function f (x) may describe a relation between a position x of the pattern and an expected emerging incident radiation. The autocorrelation function (y) at a position y of the pattern may be calculated by using the function (y) = f d ² x f(x)f(x + y).

The at least one characteristic extension of the pattern may have a correlation length between 1 mm to 5 cm, particularly for an optical measurement device having a measurement spot having a diameter of 1 cm. The correlation length may be determined from evaluating the autocorrelation function (y).

The at least one characteristic extension of the pattern may be determined by using at least one known measurement spot of the optical measurement device. The at least one known measurement spot of the optical measurement device may be known, when the size, specifically the effective size, of the at least one measurement spot of the optical measurement device may be known.

For determining the characteristic value a known relationship between the degree of variation of the plurality of optical signals and the characteristic value to be determined may be evaluated. The term “known relationship” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a link between the degree of variation of the plurality of optical signals, specifically the interim value, and the characteristic value to be determined. The known relationship may be a function that links the degree of variation of the plurality of optical signals, specifically the interim value, to the characteristic value to be determined. The known relationship may be determined from a theoretical model. The degree of variation of the plurality of optical signal may be normalized to fit the theoretical model. The normalization may be performed by using the average of the optical signals. The relationship may be provided between the degree of variation of the plurality of optical signals, specifically the interim value, and a further interim value, wherein the further interim value may be determined by using at least one of: the at least one characteristic extension of the pattern; or the size of the at least one measurement spot of the optical measurement device. The further interim value may be a further ratio using the at least one characteristic extension of the pattern and the size of the at least one measurement spot of the optical measurement device. Alternatively or in addition, the further ratio may be a further quotient of the size of the at least one measurement spot of the optical measurement device and the at least one characteristic extension of the pattern, or vice versa. The further interim value may be a further quotient of the size of the at least one measurement spot of the optical measurement device and the at least one characteristic extension of the pattern.

The known relationship may be determined by considering an expected optical signal S(y). The expected optical signal S(y) may be determined by considering a cross-correlation between the function f (x) describing the at least one characteristic extension of the pattern and a function g(x) describing the measurement spot, particularly the collection efficiency of the measurement spot at a position x of a surface of the sample within the field of view of the optical measurement device. The expected optical signal S(y) may be determined by using the function

The expected optical signal S(y) may be calculated for a plurality of positions {y}. The interim value as SD(S)/MEAN(S) may then be determined for the plurality of positions {y}. The term “collection efficiency” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to the sensitivity of the optical measurement device to the incident radiation at the position x of the surface of the sample within the field of view of the optical measurement device. The sensitivity may depend on the position of the measurement spot of the field of view, at which the incident radiation may emerge. Alternatively or in addition, the known relationship may be determined in a measurement.

The known relationship may additionally be smoothed. The term “smoothing” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to creating an approximating relationship that attempts to capture important patterns, while leaving out noise or other fine-scale structures/rapid phenomena.

The function f (x) describing the at least one characteristic extension of the pattern may describe a relation between a position x of the pattern and an expected emerging radiation. The function g(x) describing the measurement spot may be assuming a constant collection efficiency to the incident radiation over the entire at least one measurement spot. Assuming a constant collection efficiency to the incident radiation over the entire at least one measurement spot may be performed by considering an effective collection area A _eff for the measurement spot of the optical measurement device. The effective collection area A _eff may be given by the equation wherein g x) denotes the collection efficiency of the optical measurement device.

The degree of variation of the plurality of optical signals may be evaluated for determining the type of the pattern to be used in a subsequent measurement cycle. The term “measurement cycle” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a sequence of at least the steps (i) and (ii). For evaluating the type of the pattern to be used in a subsequent measurement, the degree of variation of the plurality of optical signals may be monitored to exceeds or fall below a threshold. In case the plurality of optical signals exceeds or fall below a threshold the type of the pattern to be used in the subsequent measurement cycle may be chosen. It may be evaluated that the type of the pattern may be a dot grid if the interim value, particularly the ratio, more particularly the quotient, is above 0.2, 0.3, or 0.4. It may be evaluated that the type of the pattern may be a speckle pattern if the interim value, particularly the ratio, more particularly the quotient, is below 0.8, 0.7, or 0.6.

The optical resolution of the optical measurement device may be determined by using the at least one characteristic extension of the pattern. The at least one characteristic extension of the pattern may be known. The at least one known characteristic extension of the pattern may be selected from at least one of: the size of the plurality of the features, specifically the typical structure size, more specifically a correlation length of the features; or the distribution of the plurality of the features.

The optical resolution of the optical measurement device may be determined by evaluating the degree of variation of the plurality of optical signals. A presence of variations of the plurality of optical signals may indicate that the optical resolution is around or below the at least one characteristic extension. The steps (i) and (ii) may be repeated by using a pattern having at least one different characteristic extension until a threshold is determined at which the presence of variations of the plurality of optical signals occurs for the first time or for the last time.

A distance between the sample and the optical measurement device, specifically an entrance for the incident radiation into the optical measurement device, during recording the plurality of the optical signals from at least two different portions on the sample may be constant, particularly having a maximum deviation of 10 %, 5 %, 2 %, 1 %, or 0.5%. The plurality of the recorded optical signals are being recorded by observing at least 5; 10; 20 different portions of the sample, particularly at least 5; 10; 20 different portions for each at least one optical channel. For determining the characteristic value of the optical system a first characteristic extension of a first pattern having a first correlation length may be recorded and, particularly subsequently, a second characteristic extension of a second pattern having a second correlation length may be recorded, wherein the first correlation length and the second correlation length may be different from each other. Additionally a third characteristic extension of a third pattern having a third correlation length may be recorded, wherein the third correlation length, the first correlation length and the second correlation length may be different from each other. The respective patterns may be comprised by the same sample or at least two different samples. The results on the characteristic value of the optical system received for each respective pattern in different measurement cycles may be correlated. The first characteristic extension or the second characteristic extension may be selected to have a respective correlation length having an order of magnitude that may be smaller, the same or larger than the measurement spot or the resolution of the optical measurement device.

The term “order of magnitude” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a power of ten with respect to their base unit. Exemplarily, the number 0.2 equals the expression 2 * 10 ^-1 , wherein the order of magnitude may be considered as -1.

The optical measurement device may be selected from at least one of: a spectrometer; an optical flux meter; a measurement device for flight time; a LIDAR; a distance sensor; an information transmission line; a power transmission line; an optical sensor, particularly selected for measuring of at least one of: an optical flux, an intensity, an irradiance, a radiance, a photometric and/or a radiometric quantity; or a microscope.

A detectable spectrum of the incident radiation may be ranging from at least one of: from 400 nm to 10 pm, specifically from 400 nm to 1 pm; from 900 nm to 3 pm, specifically wherein the at least two pixelated sensors are PbS sensors; or from 600 nm to 5 pm, specifically wherein the at least two pixelated sensors are PbSe sensors. The term “detectable spectrum” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a range of wavelength for which the optical measurement device generates optical signals.

The method may be computer-implemented, particularly wherein at least one of the steps (i) or (ii) may be computer-implemented. Thus, specifically, one, more than one or even all of method steps (i) and (ii) as indicated above may be performed by using a computer or a computer network, preferably by using a computer program. Thus, generally, any of the method steps (i) and (ii) including provision and/or manipulation of data may be performed by using a computer or computer network. Generally, these method steps may include any of the method steps, typically except for method steps requiring manual work, such as providing the samples and/or certain aspects of performing the actual measurements. In a further aspect of the present invention, an optical measurement device having a characteristic value is disclosed, wherein the characteristic value is determined by performing the method for determining a characteristic value of an optical system. The characteristic value may be at least one measurement spot, particularly a size of the at least one measurement spot; or an optical resolution. The optical measurement device may be selected from at least one of: a spectrometer; an optical flux meter; a measurement device for flight time; a LIDAR; a distance sensor; an information transmission line; a power transmission line; an optical sensor, particularly selected for measuring of at least one of: an optical flux, an intensity, an irradiance, a radiance, a photometric and/or a radiometric quantity; or a microscope. Definitions or characteristics of the method for determining a characteristic value of an optical system may also apply to the optical measurement device. Typically, this may further apply to any embodiments and any claim, presented in the below.

In a further aspect of the present invention, an evaluation device for determining a characteristic value of an optical system is disclosed, wherein the evaluation device is configured for carrying out a method for determining a characteristic value of an optical system. Definitions or characteristics of the method for determining a characteristic value of an optical system may also apply to the evaluation device. Typically, this may further apply to any embodiments and any claim, presented in the below.

In a further aspect of the present invention, a computer program comprising instructions is described which, when the program is executed by the evaluation device, cause the evaluation device to perform the method for determining a characteristic value of an optical system. Definitions or characteristics of the method for determining a characteristic value of an optical system may also apply to the computer program. Typically, this may further apply to any embodiments and any claim, presented in the below. Specifically, the computer program may be stored on a computer-readable data carrier and/or on a computer-readable storage medium.

As used herein, the terms “computer-readable data carrier” and “computer-readable storage medium” specifically may refer to a non-transitory data storage means, such as a hardware storage medium having stored thereon computer-executable instructions. The computer- readable data carrier or storage medium specifically may be or may comprise a storage medium such as a random-access memory (RAM) and/or a read-only memory (ROM).

In a further aspect of the present invention, a computer-readable storage medium comprising instructions which, when the program is executed by the evaluation device, cause the evaluation device to perform the method for determining a characteristic value of an optical system. Definitions or characteristics of the method for determining a characteristic value of an optical system may also apply to the computer-readable storage medium. Typically, this may further apply to any embodiments and any claim, presented in the below.

In a further aspect of the present invention, a use of a sample for performing the method for determining a characteristic value of an optical system is described, wherein the sample comprises a pattern having at least one characteristic extension. Definitions or characteristics of the method for determining a characteristic value of an optical system may also apply to the computer-readable storage medium. Typically, this may further apply to any embodiments and any claim, presented in the below.

With respect to the prior art, the method for determining a characteristic value of an optical system, the optical measurement device, the evaluation device, the computer program, the computer-readable storage medium and the use of a sample for performing a method for determining a characteristic value of an optical system according to the present invention exhibit the advantage of a reliable, fast and efficient approach for determining the characteristic value of an optical system and an optical measurement device.

In particular, the method may enable the determination of a single effective quantity for the field of view of an optical measurement device. Thereby, the of the method may not determine a distribution of collected optical signals as a degree of the characteristic value. Instead, the method may yield a single effective quantity which may reflect a similarity of optical signal collection, particularly light collection, for a specific application.

As used herein, the terms “have”, “comprise” or “include” or any arbitrary grammatical variations thereof are used in a non-exclusive way. Thus, these terms may both refer to a situation in which, besides the feature introduced by these terms, no further features are present in the entity described in this context and to a situation in which one or more further features are present. As an example, the expressions “A has B”, “A comprises B” and “A includes B” may both refer to a situation in which, besides B, no other element is present in A (i.e. a situation in which A solely and exclusively consists of B) and to a situation in which, besides B, one or more further elements are present in entity A, such as element C, elements C and D or even further elements.

Further, it shall be noted that the terms “at least one”, “one or more” or similar expressions indicating that a feature or element may be present once or more than once typically will be used only once when introducing the respective feature or element. Herein, in most cases, when referring to the respective feature or element, the expressions “at least one” or “one or more” will not be repeated, notwithstanding the fact that the respective feature or element may be present once or more than once.

Further, as used herein, the terms "preferably", "more preferably", "particularly", "more particularly", "specifically", "more specifically" or similar terms are used in conjunction with optional features, without restricting alternative possibilities. Thus, features introduced by these terms are optional features and are not intended to restrict the scope of the claims in any way. The invention may, as the skilled person will recognize, be performed by using alternative features. Similarly, features introduced by "in an embodiment of the invention" or similar expressions are intended to be optional features, without any restriction regarding alternative embodiments of the invention, without any restrictions regarding the scope of the invention and without any restriction regarding the possibility of combining the features introduced in such way with other optional or non-optional features of the invention. Summarizing and without excluding further possible embodiments, the following embodiments may be envisaged:

Embodiment 1 : A method for determining a characteristic value of an optical system, wherein the optical system comprises a sample and an optical measurement device, wherein the optical measurement device is configured for measuring a plurality of optical signals generated from different portions of the sample, the method comprising the following steps:

(i) providing data comprising information about a plurality of optical signals, wherein each optical signal is generated by at least one channel of the optical measurement device using incident radiation generated from a portion of the sample, wherein at least two of the optical signals are recorded from different portions of the sample by directing at least one measurement spot of the field of view of the optical measurement device to the different portions of the sample, wherein the sample comprises at least one pattern having at least one characteristic extension, wherein the at least two of the optical signals depend on the at least one characteristic extension of the pattern and on a size of the at least one measurement spot directed to the different portions of the sample;

(ii) determining a characteristic value of the optical system by evaluating a degree of variation of the plurality of optical signals; wherein evaluating the degree of variation of the plurality of optical signals comprises determining an interim value by using an average of the plurality of the optical signals and the standard deviation of the plurality of the optical signals.

Embodiment 2: The method according to the preceding method embodiment,

- wherein the at least two of the optical signals are recorded by the same at least one channel; or

- wherein the optical measurement device comprises a plurality of channels and the at least two of the optical signals are recorded by different channels of the plurality of channels.

Embodiment 3: The method according to any one of the preceding method embodiments, wherein the degree of variation of the plurality of optical signals is evaluated by analyzing at least one of:

- a standard deviation of the plurality of the optical signals;

- a variance of the plurality of the optical signals;

- a maximum intensity optical signal of the plurality of the optical signals;

- a minimum intensity optical signal of the plurality of the optical signals;

- a difference between two optical signals of the plurality of the optical signals, particularly a difference between the maximum intensity optical signal and the minimum intensity optical signal;

- a distribution of the plurality of the optical signals, particularly a skewness of the distribution or a kurtosis of the distribution; or an analytical function, particularly an analytical function considering the maximum intensity optical signal of the plurality of the optical signals or the minimum intensity optical signal of the plurality of the optical signals.

Embodiment 4: The method according to anyone of the preceding method embodiment, wherein the interim value is a ratio using the standard deviation and the average, or wherein the interim value is a quotient of the standard deviation divided by the average.

Embodiment 5: The method according to anyone of the preceding method embodiments, wherein the at least one pattern comprised by the sample has a plurality of features generating the at least one characteristic extension, wherein the features generates at least one optical signal.

Embodiment 6: The method according to anyone of the preceding method embodiments, wherein the pattern is arranged on a background, wherein the background is further comprised by the sample.

Embodiment 7: The method according to the preceding method embodiment, wherein the background generates no optical signal, or wherein the background generates at least one further optical signal which is distinguishable from the at least one optical signal generated by the at least one characteristic extension, particularly the features.

Embodiment 8: The method according to the preceding method embodiment, wherein the at least one further optical signal has at least one distinguishable optical property selected from at least one of:

- an intensity;

- a polarization;

- a spectral flux;

- an irradiance ;

- a radiance; or

- an optical flux of the incident radiation.

Embodiment 9: The method according to anyone of the four preceding method embodiments, wherein each feature of the plurality of the features generates optical signals having an identical optical property, particularly with a maximum deviation of 10 %, 5 %, 2 %, 1 %, or 0.5%.

Embodiment 10: The method according to the preceding method embodiments, wherein the identical optical property is selected from at least one of:

- an intensity;

- a polarization;

- a spectral flux;

- an irradiance;

- a radiance; or - an optical flux of the incident radiation.

Embodiment 11 : The method according to anyone of the preceding method embodiments, wherein the characteristic value is selected from corresponding to at least one of:

- the at least one measurement spot, particularly the size of the at least one measurement spot of the optical measurement device;

- an optical resolution of the optical measurement device; or

- the characteristic extension of the pattern in the sample.

Embodiment 12: The method according to anyone of the preceding method embodiments, wherein the size of at least one measurement spot of the optical measurement device is an effective size assuming a constant sensitivity to the incident radiation over the entire at least one measurement spot.

Embodiment 13: The method according to anyone of the eight preceding method embodiments, wherein the characteristic value corresponds to the characteristic extension of the pattern which is provided by the plurality of the features, wherein the size of the plurality of the features is a typical structure size.

Embodiment 14: The method according to anyone of the three preceding method embodiments, wherein the size of the at least one measurement spot of the optical measurement device is determined by evaluating the at least one characteristic extension of the pattern.

Embodiment 15: The method according to anyone of the preceding method embodiments, wherein the at least one characteristic extension of the pattern, preferably selected from at least one of:

- the size of the plurality of the features, specifically the typical structure size, more specifically a correlation length of the features; or

- the distribution of the plurality of the features; is known.

Embodiment 16: The method according to anyone of the preceding method embodiments, wherein a type of the pattern is selected from at least one of:

- a dot grid, wherein the plurality of the features are dots comprised by the dot grid; or

- a speckle pattern, wherein the plurality of the features are grains comprised by the speckle pattern.

Embodiment 17: The method according to the preceding method embodiments, wherein the plurality of the features of the dot grid have the same size, specifically the same diameter, particularly with a maximum deviation of 10 %, 5 %, 2 %, 1 %, or 0.5 %. Embodiment 18: The method according to anyone of the two preceding method embodiments, wherein the plurality of the features of the dot grid have the same distance to at least one neighboring feature, specifically any neighboring feature, particularly with a maximum deviation of 10 %, 5 %, 2 %, 1 %, or 0.5 %.

Embodiment 19: The method according to anyone of the preceding method embodiments, wherein the pattern is a grey-scale pattern.

Embodiment 20: The method according to anyone of the preceding method embodiments, wherein the at least one characteristic extension of the pattern is described by using a function f (x) that describes a relation between a position x of the pattern and an expected emerging radiation, wherein an autocorrelation function 4(y) of the function f(x) is identical for at least two positions y of the pattern or each position y of the pattern, particularly with a maximum deviation of 10%, 5%; 2%, 1 % or 0.5%.

Embodiment 21 : The method according to anyone of the preceding method embodiments, the at least one characteristic extension of the pattern has a correlation length between 1 mm to 5 cm, particularly for an optical measurement device having a measurement spot having a diameter of 1 cm .

Embodiment 22: The method according to anyone of the eleven preceding method embodiments, wherein the at least one characteristic extension of the pattern is determined by using at least one known measurement spot of the optical measurement device.

Embodiment 23: The method according to the preceding method embodiments, wherein the at least one known measurement spot of the optical measurement device is known, when the size, more specifically the effective size, of the at least one known measurement spot is known.

Embodiment 24: The method according to anyone of the preceding method embodiments, wherein for determining the characteristic value a known relationship between the degree of variation of the plurality of optical signals and the characteristic value to be determined is evaluated.

Embodiment 25: The method according to the preceding method embodiment, wherein the relationship is provided between the degree of variation of the plurality of optical signals, specifically the interim value, and a further interim value, wherein the further interim value is determined by using at least one of:

- the at least one characteristic extension of the pattern; or

- the size of the at least one measurement spot of the optical measurement device.

Embodiment 26: The method according to the preceding method embodiment, wherein the further interim value is a further ratio using the at least one characteristic extension of the pattern and the size of the at least one measurement spot of the optical measurement device, or wherein the further interim value is a further quotient of the size of the at least one measurement spot of the optical measurement device and the at least one characteristic extension of the pattern.

Embodiment 27: The method according to anyone of the three preceding method embodiments, wherein the known relationship is determined by considering an expected optical signal S(y), particularly wherein the expected optical signal S(y) is determined by considering a cross-correlation between a function f (x) describing the at least one characteristic extension of the pattern and a function g(x) describing the measurement spot, particularly the collection efficiency of the measurement spot at a position x.

Embodiment 28: The method according to the preceding method embodiment, wherein the function f(x) describing the at least one characteristic extension of the pattern describes a relation between a position x of the pattern and an expected emerging radiation.

Embodiment 29: The method according to anyone of the two preceding method embodiments, wherein the function g(x) describing the measurement spot is determined by assuming a constant collection sensitivity to the incident radiation over the entire at least one measurement spot.

Embodiment 30: The method according to the preceding method embodiment, wherein assuming a constant sensitivity to the incident radiation over the entire at least one measurement spot is performed by considering an effective collection area A _eff for the at least one measurement spot of the optical measurement device.

Embodiment 31 : The method according to anyone of the seven preceding method embodiments, wherein the known relationship is additionally smoothed.

Embodiment 32: The method according to anyone of the preceding method embodiments, wherein the degree of variation of the plurality of optical signals is evaluated for determining the type of the pattern to be used in a subsequent measurement cycle.

Embodiment 33: The method according to the preceding method embodiment, wherein it is evaluated that the type of the pattern used in a subsequent measurement cycle is a dot grid if the interim value, particularly the ratio, more particularly the quotient, is above 0; 1 ; 2; 3; 4; 5; 6; 7; 8; 9; or 10.

Embodiment 34: The method according to anyone of the two preceding method embodiments, wherein it is evaluated that the type of the pattern used in a subsequent measurement cycle is a speckle pattern if the interim value, particularly the ratio, more particularly the quotient, is below 0; 1 ; 2; 3; 4; 5; 6; 7; 8; 9; or 10.

Embodiment 35: The method according to anyone of the twenty four preceding method embodiments, wherein the optical resolution of the optical measurement device is determined by using the at least one characteristic extension of the pattern. Embodiment 36: The method according to the preceding method embodiment, wherein the at least one characteristic extension of the pattern, preferably selected from at least one of:

- the size of the plurality of the features, specifically the typical structure size, more specifically a correlation length of the features; or

- the distribution of the plurality of the features; is known.

Embodiment 37: The method according to anyone of the two preceding method embodiments, wherein the optical resolution of the optical measurement device is determined by evaluating the degree of variation of the plurality of optical signals.

Embodiment 38: The method according to the preceding method embodiment, wherein a presence of variations of the plurality of optical signals indicates that the optical resolution is around or below the at least one characteristic extension.

Embodiment 39: The method according to anyone of the two preceding method embodiments, wherein the steps (i) and (ii) are repeated by using a pattern having at least one different characteristic extension until a threshold is determined at which the presence of variations of the plurality of optical signals occurs for the first time or for the last time.

Embodiment 40: The method according to anyone of the preceding method embodiments, wherein a distance between the sample and the optical measurement device, specifically an entrance for the incident radiation into the optical measurement device, during recording the plurality of the optical signals from at least two different portions on the sample is constant, particularly having a maximum deviation of 10%, 5%; 2%, 1% or 0.5%.

Embodiment 41 : The method according to anyone of the preceding method embodiments, wherein the plurality of the recorded optical signals are being recorded by observing at least 5; 10; 20 different portions of the sample, particularly at least 5; 10; 20 different portions for each at least one optical channel.

Embodiment 42: The method according to anyone of the preceding method embodiments, wherein for determining the characteristic value of the optical system a first characteristic extension of a first pattern having a first correlation length is recorded and, particularly subsequently, a second characteristic extension of a second pattern having a second correlation length is recorded, wherein the first correlation length and the second correlation length are different from each other.

Embodiment 43: The method according to the preceding method embodiments, wherein the first characteristic extension or the second characteristic extension is selected to have a respective correlation length having an order of magnitude that is smaller, the same or larger than the measurement spot or the resolution of the optical measurement device. Embodiment 44: The method according to anyone of the preceding method embodiments, wherein the optical measurement device is selected from at least one of:

- a spectrometer;

- an optical flux meter;

- a measurement device for flight time;

- a LIDAR;

- a distance sensor;

- an information transmission line;

- a power transmission line;

- an optical sensor, particularly selected for measuring of at least one of: an optical flux, an intensity, an irradiance, a radiance, a photometric and/or a radiometric quantity; or

- a microscope.

Embodiment 45: The method according to anyone of the preceding method embodiments, wherein a detectable spectrum of the incident radiation is ranging from at least one of:

- 400 nm to 10 pm, specifically from 400 nm to 1 pm;

- 900 nm to 3 pm, specifically wherein the at least two pixelated sensors are PbS sensors; or

- 600 nm to 5 pm, specifically wherein the at least two pixelated sensors are PbSe sensors.

Embodiment 46: The method according to anyone of the preceding method embodiments, wherein the method is computer-implemented, particularly wherein at least one of the steps (i) or (ii) is computer-implemented.

Embodiment 47: An optical measurement device having a characteristic value, particularly selected from at least one of:

- at least one measurement spot, particularly a size of the at least one measurement spot; or

- an optical resolution, wherein the characteristic value is determined by performing a method for determining a characteristic value of an optical system according to anyone of the preceding embodiments.

Embodiment 48: The optical measurement device according to the preceding embodiment, wherein the optical measurement device is selected from at least one of:

- a spectrometer;

- an optical flux meter;

- a measurement device for flight time;

- a LIDAR;

- a distance sensor;

- an information transmission line;

- a power transmission line;

- an optical sensor, particularly selected for measuring of at least one of: an optical flux, an intensity, an irradiance, a radiance, a photometric and/or a radiometric quantity; or - a microscope.

Embodiment 49: An evaluation device for determining a characteristic value of an optical system, wherein the evaluation device is configured for carrying out a method for determining a characteristic value of an optical system according to anyone of the preceding method embodiments.

Embodiment 50: A computer program comprising instructions which, when the program is executed by an evaluation device according to anyone of the preceding embodiments referring to an evaluation device, cause the evaluation device to perform the method for determining a characteristic value of an optical system according to anyone of the preceding embodiments referring to a method.

Embodiment 51 : A computer-readable storage medium comprising instructions which, when the program is executed by the evaluation device according to anyone of the preceding embodiments referring to an evaluation device, cause the evaluation device to perform the method for determining a characteristic value of an optical system according to anyone of the preceding embodiments referring to a method.

Embodiment 52: Use of a sample for performing a method for determining a characteristic value of an optical system according to anyone of the preceding embodiments referring to a method, wherein the sample comprises a pattern having at least one characteristic extension.

Short description of the Figures

Further optional features and embodiments will be disclosed in more detail in the subsequent description of embodiments, preferably in conjunction with the dependent claims. Therein, the respective optional features may be realized in an isolated fashion as well as in any arbitrary feasible combination, as the skilled person will realize. The scope of the invention is not restricted by the preferred embodiments. The embodiments are schematically depicted in the Figures. Therein, identical reference numbers in these Figures refer to identical or functionally comparable elements.

In the Figures:

Fig. 1a-1c show exemplary optical systems each comprising a sample and an optical measurement device;

Fig. 2 shows exemplary variations of optical signals generated by an optical measurement device;

Fig. 3 shows an exemplary method for determining a characteristic value of an optical system; Fig. 4a-4c show an exemplary dot grid pattern, an autocorrelation function of the exemplary dot grid pattern and a known relationship between a degree of variation of the optical signals and the characteristic value to be determined for the exemplary dot grid pattern; and

Fig. 5a-5c show an exemplary speckle pattern, an autocorrelation function of the exemplary speckle pattern and a known relationship between a degree of variation of the optical signals and the characteristic value to be determined for the exemplary speckle pattern.

Detailed description of the embodiments

According to Fig. 1a, an exemplary optical system 100 may comprise a sample 200 and an optical measurement device 300. The optical measurement device 300 may be configured for measuring an optical signal 302 generated from a portion of the sample 200 from which radiation 206 emerges that may be incident into the optical measurement device 300. The optical signal 302 may be recorded from the portion of the sample 200 by directing at least one measurement spot 304 of a field of view 306 of the optical measurement device 300 on the portion of the sample 200. The exemplary optical measurement device 300 may comprise one field of view 306 that may be assigned to one channel of the optical measurement device 300. The optical signal 302 may be generated by the one channel of the optical measurement device 300.

The sample 200 may be a granular sample 200. The radiation 206 may vary due to the granularity of the sample 200, as indicated by using the different line styles for the radiation 206. The granular sample 200 may comprise constituents 202, wherein at least a part of the constituents 202 may be features 208 comprised by a pattern 214 generating at least one characteristic extension 212. The constituents 202 may be distant to one another, thereby the constituents 202 may introduce a typical length scale 204 that may be influenced by the granularity of the sample 200. The size of the measurement spot 304, particularly the diameter of the measurement spot 304, may be larger than the typical length scale 204. Thereby, the granularity of the sample 200 averages out and the optical signal 302 may not be influenced by the granularity of the sample 200. As a result, the optical signal 302 may be identical to an optical signal 302 that may be generated from a different portion of the sample 200.

A characteristic value of the exemplary optical system 100 may be determined by an evaluation device 310, particularly be evaluating the variations of a plurality of optical signals 302 generated by different portions of the sample 200. Thus, the evaluation device 310 may be configured for carrying out a method 400 for determining a characteristic value of the optical system 100. The method 400 is described below in more detail.

The optical measurement device 300 may be selected from at least one of: a spectrometer; an optical flux meter; a measurement device for flight time; a LIDAR; a distance sensor; an information transmission line; a power transmission line; an optical sensor, particularly selected for measuring of at least one of: an optical flux, an intensity, an irradiance, a radiance, a photometric and/or a radiometric quantity; or a microscope. A detectable spectrum of the incident radiation 206 may be ranging from at least one of: from 400 nm to 10 pm, specifically from 400 nm to 1 pm; from 900 nm to 3 pm, specifically wherein the at least two pixelated sensors are PbS sensors; or from 600 nm to 5 pm, specifically wherein the at least two pixelated sensors are PbSe sensors.

According to Fig. 1 b the size of the measurement spot 304, particularly the diameter of the measurement spot 304, may be smaller to the typical length scale 204 for a further exemplary optical system 100. Thereby, the granularity of the sample 200 may not averages out and the optical signal 302 may be influenced by the granularity of the sample 200. As a result, the optical signal 302 may variate compared to an optical signal 302 that may be recorded at a different portion of the sample 200.

According to Fig. 1c an exemplary optical measurement device 300 may comprise a plurality of channels that each generate individual optical signals 302. Each channel may be assigned a field of view 306.

In Fig. 2 the optical signals 302 of four channels of an exemplary optical measurement device 300 are depicted. The optical channels may correspond to a range of pixels that are depicted on the horizontal axis 312. A first optical channel may range from pixel 45 to pixel 85. A second optical channel may range from pixel 86 to pixel 130. A third optical channel may range from pixel 131 to pixel 175. A fourth optical channel may range from pixel 176 to pixel 220. On the vertical axis 314 the value of the optical signal 302 is depicted. The optical signals 302 may be generated from three different portions of the sample 200 as indicated by using the three different line styles. The optical signals 302 generated from three different portions of the sample 200 may variate.

In Fig. 3 a method 400 for determining a characteristic value of an optical system 100 is depicted, wherein the optical system 100 comprises a sample 200 and an optical measurement device 300, wherein the optical measurement device 300 is configured for measuring a plurality of optical signals 302 generated from different portions of the sample 200, the method 400 comprising the following steps:

(i) in a providing step 402, data comprising information about a plurality of optical signals 302 is provided, wherein each optical signal 302 is generated by at least one channel of the optical measurement device 300 using incident radiation 206 generated from a portion of the sample 200, wherein at least two of the optical signals 302 are recorded from different portions of the sample 200 by directing at least one measurement spot 304 of the field of view 306 of the optical measurement device 300 to the different portions of the sample 200, wherein the sample 200 comprises at least one pattern 214 having at least one characteristic extension 212, wherein the at least two of the optical signals 302 depend on the at least one characteristic extension 212 of the pattern 214 and on a size of the at least one measurement spot 304 directed to the different portions of the sample 200;

(ii) in a determining step 404, a characteristic value of the optical system 100 by evaluating a degree of variation of the plurality of optical signals 302 is determined. The characteristic value may corresponds to the characteristic extension 212 of the pattern 214 which may be provided by a plurality of features 208, wherein the size of the plurality of the features 208 may be a typical structure size.

The at least two of the optical signals may be recorded by the same at least one channel. Alternatively the optical measurement device may comprise a plurality of channels and/or the at least two of the optical signals may be recorded by different channels of the plurality of channels.

The degree of variation of the plurality of optical signals 302 may be evaluated by analyzing at least one of:

- a standard deviation of the plurality of the optical signals 302; or

- a variance of the plurality of the optical signals;

- a maximum intensity optical signal of the plurality of the optical signals;

- a minimum optical signal of the plurality of the optical signals;

- a difference between two optical signals of the plurality of the optical signals, particularly a difference between the maximum intensity optical signal and the minimum optical signal;

- a distribution of the plurality of optical signals, particularly a skewness of the distribution or a kurtosis of the distribution; or

- an analytical function, particularly an analytical function considering the maximum intensity optical signal of the plurality of the optical signals or the minimum optical signal of the plurality of the optical signals.

Evaluating the degree of variation of the plurality of optical signals 302 comprises determining an interim value by using an average of the plurality of the optical signals 302 and the standard deviation of the plurality of the optical signals 302. The interim value may be a ratio using the standard deviation and the average, or the interim value may be a quotient of the standard deviation divided by the average.

The characteristic value may be selected from corresponding to at least one of:

- the at least one measurement spot 304, particularly the size of the at least one measurement spot 304 of the optical measurement device 300;

- an optical resolution of the optical measurement device 300; or

- the characteristic extension 212 of the pattern 214 in the sample 200.

The size of the at least one measurement spot 304 of the optical measurement device 300 may be determined by evaluating the at least one characteristic extension 212 of the pattern 214. Therefore, the at least one characteristic extension 212 of the pattern 214, preferably selected from at least one of: the size of the plurality of the features 208, specifically the typical structure size, more specifically a correlation length of the features 208; or the distribution of the plurality of the features 208; may be known.

The at least one characteristic extension 212 of the pattern 214 may be determined by using at least one known measurement spot 304 of the optical measurement device 300. The at least one known measurement spot 304 of the optical measurement device 300 may be known, when the size, more specifically the effective size, of the at least one known measurement spot 304 is known.

A type of the pattern 214 may be selected from a dot grid, as depicted in Fig 4a, wherein the plurality of the features 208 are dots comprised by the dot grid. Alternatively or in addition, the type of the pattern 214 may be selected from a speckle pattern, as depicted in Fig. 5a, wherein the plurality of the features 208 are grains comprised by the speckle pattern. Both patterns 214 are a grey-scale patterns.

The plurality of the features 208 of the dot grid may have the same size, specifically the same diameter, particularly with a maximum deviation of 10%, 5%; 2%, 1% or 0.5%. The plurality of the features 208 of the dot grid have the same distance to at least one neighboring feature 206, specifically any neighboring feature 208, particularly with a maximum deviation of 10%, 5%; 2%, 1 % or 0.5%.

Generally, the at least one pattern 214 comprised by the sample 200 may have a plurality of features 208 generating the at least one characteristic extension 212, wherein the features 208 may generate at least one optical signal 302.

The pattern 214 may be arranged on a background 210, wherein the background 210 may be further comprised by the sample 200. The background 210 may generate no optical signal 302. Alternatively, the background 210 may generate at least one further optical signal 302 which may be distinguishable from the at least one optical signal 302 generated by the at least one characteristic extension 212, particularly the features 208.

The at least one further optical signal 302 may have at least one distinguishable optical property selected from at least one of: an intensity; a polarization; a spectral flux; an irradiance; a radiance; or an optical flux of the incident radiation 206. Each feature of the plurality of the features 208 may generate optical signals 302 having an identical optical property, particularly with a maximum deviation of 10%, 5%; 2%, 1% or 0.5%. The identical optical property may be selected from at least one of: an intensity; a polarization; a spectral flux; an irradiance; a radiance; or an optical flux of the incident radiation 206.

An autocorrelation function 500 of the dot grid is depicted in Fig 4b. On the horizontal axis 502 of the autocorrelation function 500 dx divided by the radius of the dots is shown. On the vertical axis 504 the value of the autocorrelation function may be shown. An autocorrelation function 600 of the speckle pattern is depicted in Fig 5b. On the horizontal axis 602 the autocorrelation function 600 dx divided by a length that corresponds to the Full Width at Half Maximum length of the autocorrelation function 600 divided by 2 may be shown. On the vertical axis 604 the value of the autocorrelation function may be shown.

Generally, the at least one characteristic extension 212 of the pattern 214 may be described by using a function (%) that describes a relation between a position x of the pattern 214 and an expected emerging radiation 206, wherein an autocorrelation function A(y) of the function (%) is identical for at least two positions y of the pattern 214 or each position y of the pattern 214, particularly with a maximum deviation of 10%, 5%; 2%, 1 % or 0.5%.

Generally, the at least one characteristic extension 212 of the pattern 214 may be derived from the autocorrelation function. A correlation length of the least one characteristic extension 212 may be 1 mm to 5 cm, particularly for an optical measurement device having a measurement spot having a diameter of 1 cm . Typically, a correlation length of the least one characteristic extension 212 generated by the dots of the dot grid may be 1 mm to 5 cm . Typically, a correlation length of the least one characteristic extension 212 generated by the grains of the speckle pattern may be 1 mm to 5 cm .

For determining the characteristic value a known relationship between the degree of variation of the plurality of optical signals 302 and the characteristic value to be determined may be evaluated. A known relationship 700 of the dot grid is depicted in Fig 4c. On a horizontal axis 702 the diameter of the dots of the dot grid divided by the diameter of the measurement spot 304 may be shown. On a vertical axis 704 the quotient of the standard deviation SD(S) divided by the average of the optical signals MEAN(S) may be shown.

A known relationship 800 of the speckle pattern is depicted in Fig 5c. On the horizontal axis 802 the length that corresponds to the Full Width at Half Maximum length of the autocorrelation function of the speckle pattern be shown. On the vertical axis 804 the quotient of the standard deviation SD(S) divided by the average of the optical signals MEAN(S) may be shown. Generally, the relationship may be provided between the degree of variation of the plurality of optical signals 302, specifically the interim value, and a further interim value, wherein the further interim value may be determined by using at least one of: the at least one characteristic extension 212 of the pattern 214; or the size of the at least one measurement spot 304 of the optical measurement device 300. The further interim value may be a further ratio using the at least one characteristic extension 212 of the pattern 214 and the size of the at least one measurement spot 304 of the optical measurement device 300, or wherein the further interim value may be a further quotient of the size of the at least one measurement spot 304 of the optical measurement device 300 and the at least one characteristic extension 212 of the pattern 214. The known relationship may be additionally smoothed.

Generally, the known relationship may be determined by considering an expected optical signal S(y), particularly wherein the expected optical signal S(y) may be determined by considering a cross-correlation between a function f (x) describing the at least one characteristic extension 212 of the pattern 214 and a function g(x) describing the measurement spot 304, particularly the collection efficiency of the measurement spot 304 at a position x. The function (%) describing the at least one characteristic extension 212 of the pattern 214 may describe a relation between a position x of the pattern 214 and an expected emerging radiation 206. The function g(x) may describe the measurement spot 304 is determined by assuming a constant collection sensitivity to the incident radiation 206 over the entire at least one measurement spot 304.

The degree of variation of the plurality of optical signals 302 may be evaluated for determining the type of the pattern 214 to be used in a subsequent measurement cycle. Therefore it may be monitored if the degree of variation of the plurality of optical signals 302 exceeds or falls below a threshold. It may be evaluated that the type of the pattern 214 used in a subsequent measurement cycle may be a dot grid if the interim value, particularly the ratio, more particularly the quotient, is above 0.2, 0.3 or 0.4. Alternatively or in addition, it may be evaluated that the type of the pattern 214 used in a subsequent measurement cycle may be a speckle pattern if the interim value, particularly the ratio, more particularly the quotient, is below 0.8, 0.7 or 0.6.

The optical resolution of the optical measurement device 300 may be determined by using the at least one characteristic extension 212 of the pattern 214. The at least one characteristic extension 212 of the pattern 214, preferably selected from at least one of: the size of the plurality of the features 208, specifically the typical structure size, more specifically a correlation length of the features 208; or the distribution of the plurality of the features 208; may be known. The optical resolution of the optical measurement device 300 may be determined by evaluating the degree of variation of the plurality of optical signals 302. A presence of variations of the plurality of optical signals 302 may indicate that the optical resolution is around or below the at least one characteristic extension 212. The steps (i) and (ii) may be repeated by using a pattern 214 having at least one different characteristic extension 212 until a threshold may be determined at which the presence of variations of the plurality of optical signals 302 occurs for the first time or for the last time.

A distance between the sample 200 and the optical measurement device 300, specifically an entrance for the incident radiation 206 into the optical measurement device 300, during recording the plurality of the optical signals 302 from at least two different portions on the sample 200 may be constant, particularly having a maximum deviation of 10%, 5%; 2%, 1 % or 0.5%. Thereby, the measurement spot 304 on the sample 200 may remain constant during the recording of the plurality of the optical signals 302. The plurality of the recorded optical signals 302 may be recorded by observing at least 5; 10; 20 different portions of the sample 200, particularly at least 5; 10; 20 different portions for each at least one optical channel.

For determining the characteristic value of the optical system a first characteristic extension of a first pattern having a first correlation length may be recorded and, particularly subsequently, a second characteristic extension of a second pattern having a second correlation length may be recorded, wherein the first correlation length and the second correlation length may be different from each other. Additionally a third characteristic extension of a third pattern having a third correlation length may be recorded, wherein the third correlation length, the first correlation length and the second correlation length may be different from each other. The respective patterns may be comprised by the same sample or different samples. The results on the characteristic value of the optical system received for each respective pattern may be correlated. The first characteristic extension or the second characteristic extension may be selected to have a respective correlation length having an order of magnitude that may be smaller, the same or larger than the measurement spot or the resolution of the optical measurement device.

The method 400 may be computer-implemented, particularly at least one of the steps (i) or (ii) may be computer-implemented. Therefore, a computer program may be available, wherein the computer program comprises instructions which, when the program may be executed by an evaluation device 310, cause the evaluation device 310 to perform the method 400 for determining a characteristic value of an optical system 100. The computer program may be provided on a computer-readable storage medium that may comprise instructions which, when the program may be executed by the evaluation device 310, cause the evaluation device 310 to perform the method 400 for determining a characteristic value of an optical system 100.

List of reference numbers

100 optical system 200 sample 202 constituent 204 typical length scale 206 radiation, incident radiation 208 features 210 background 212 characteristic extension 214 pattern 300 optical measurement device 302 optical signal 304 measurement spot 306 field of view 310 evaluation device 312 horizontal axis 314 vertical axis

400 method 402 providing step 404 determining step 500 autocorrelation function of the dot grid 502 horizontal axis 504 vertical axis 600 autocorrelation function of the speckle pattern 602 horizontal axis 604 vertical axis 700 known relationship of the dot grid pattern 702 horizontal axis 704 vertical axis 800 known relationship of the speckle pattern 802 horizontal axis 804 vertical axis