Technical Field

The invention relates to a disposable protective cover, specifically for use in a hand-held spec trometer device or in a hand-held spectrometer system and/or for use with a hand-held spec trometer device, to a hand-held spectrometer system comprising the disposable protective cov er and a hand-held spectrometer device. The invention further relates to a use of the hand-held spectrometer system, to a method for protecting a hand-held spectrometer device and to a method for spectroscopic analysis of at least one sample. Such devices, systems and methods can, in general, be employed for investigation or monitoring purposes, in particular, in the infra red (IR) spectral region, especially in the near-infrared (N IR) and the mid-infrared (MidIR) spec tral regions, and for a detection of heat, flames, fire, or smoke. However, further kinds of appli cations are possible.

Background art

Various spectrometer devices and systems for investigations in the infrared (IR) spectral region, especially in the near-infrared (N IR) spectral region, are known. The spectrometer devices and systems generally comprise one or more wavelength-selective elements for separating incident light into a spectrum of constituent wavelengths and one or more detected devices for detecting the constituent wavelengths, such as one or more prisms, gratings, filters or the like. Especially, spectrometer devices which comprise a combination of a linearly variable filter (LVF) and a de tector array have already been proposed. Herein, the LVF is designated for separating light cap tured from an object, also referred to as a sample, into a spectrum of constituent wavelength signals while the detector array includes a plurality of pixels, wherein each of the plurality of pixels is disposed to receive at least a portion of a plurality of the constituent wavelength signals that provides a power reading for each constituent wavelength. Typically, in order to accomplish that the incident light may impinge the LVF in a manner normal to a receiving surface of the LVF, a baffle is used for this purpose, which, however, generally results in a low light throughput and a poor signal-to-noise ratio.

For applications in the field, portable spectroscopic devices have been developed. Thus, as one of the various examples, US 2014/131578 A1 discloses a portable spectrometer device which includes an illumination source for directing at a sample as well as a tapered light pipe (TLP) for capturing the light which interacts with the sample at a first focal ratio and for delivering the light at a second focal ratio lower than the first focal ratio to the LVF.

Specifically the application of hand-held spectrometer devices in the field, however, may lead to challenges with respect to the contamination of sensitive parts of the spectrometer device, spe cifically in case the hand-held spectrometer directly is in contact with a sample to be analyzed, such as a liquid sample. In some cases, however, the direct contact between the hand-held spectrometer devices and the sample is advantageous, since a well-defined and short distance between the sample and the spectrometer device typically is required specifically for quantita tive measurement. Further, in general, establishing well defined sampling conditions for spec troscopic analysis of samples, specifically in the field, has turned out to be a challenge.

In other fields of technology, disposable covers for hand-held devices are known, specifically for hygienic purposes. Thus, as an example, US 6,022,140 discloses a disposable cover for an infrared thermometer. The disposable cover provides I R window isolation of handling and usage generated forces. The cover comprises a thin sidewall linked to the film window with a collar structure. The collar structure includes one or more characteristics that isolate the film window from externally applied forces or develops counter forces in a way that precludes federal stretching and other transmission distorting effects.

US 5179936 A discloses a sanitary protective cover or sheath for the ear canal probe of a tym panic thermometer. The speculum has a generally tubular body portion and an infrared trans parent membrane attached to and sealing the forward end of the body portion. While the tubular body portion is being injection molded of plastic material such as polypropylene or polyethylene, a film of a similar plastic material is mated to the forward end of the membrane and is thus sev ered from the film and one side thereof thermally bonded to the tubular body portion. At the same time a bonding ring of roughly the same diameter as the forward end of the tubular body portion is injection molded. The ring is thermally bonded to the opposite side of the film in alignment with the forward end of the tubular body portion.

US 5860421 A discloses a disposable calibration device which is used to calibrate a measure ment system which transmits radiation or acoustic waves to a material or tissue in order to effect measurements. The disposable calibration device includes a structure with a window through which the radiation or acoustic waves can be transmitted, as well as a removable calibration target arranged on the window and capable of returning a portion of the radiation or acoustic waves for calibrating the measurement system. The removable calibration target can be peeled from window to allow a measurement to be made on the material or tissue. Once a measure ment is complete, the disposable calibration device can be discarded and a new calibration de vice can be inserted on the measuring system.

WO 2015/082300 A1 discloses a device for dental use for discriminating the color of teeth, comprising: a cellular phone with a digital camera comprising a lens and a light source acting as flash, a case, a spacer mounted on the case in correspondence of the lens and the light source, a first polarization filter and a second polarization filter disposed inside the spacer, respectively on said lens and on said light source, a calibration label disposed in the spacer, a database containing a plurality of digital sample images that univocally define sample colors, and a com parison soft-ware to compare the digital image of the tooth taken with the device with said sam ple images of the database to discriminate the color of the photographed tooth.

US 2006/0152586 A1 discloses an image processing system which is used for dentistry. Upon creating a false tooth of a patient, a plurality of illuminating light of LEDs with different wave- lengths emit light and a photographing apparatus photographs a tooth portion of the patient, thereby obtaining image data. The image data is sent to a dentistry filing system serving as a processing apparatus, and color reproducing data is obtained by calculation. The color repro ducing data is sent to a dentistry factory via a public line. Data is searched from a database for calculating a ceramic compounding ratio, compound data of the ceramic false tooth is obtained, matching the color of the tooth portion of the patient, and the false tooth approximate to the tooth color of the patient is created.

The situation for thermometer covers, however, is not comparable to the situation in spectrome ter systems. Specifically, the optical requirements for spectrometer systems significantly differ from those in medical devices which basically consist in hygienic requirements and mechanical stability. Spectrometer systems, contrarily, require well-defined optical reliability and reproduci bility. Thus, optical quality and, specifically, good optical properties such as sufficient transmis sion in the infrared spectral range are a prerequisite for spectrometer components. Further, chemical inertness of materials being in contact with the sample is often essential for spectrom eter components, as well as non-sticking properties for avoiding cross-contamination of different samples.

Problem to be solved

It is therefore desirable to provide devices and methods which address the above-mentioned challenges and shortcomings of known spectrometer systems. Specifically, devices and me thods shall be proposed which enable highly reproducible spectrometer measurements in the field, under rough environmental conditions, using hand-held spectrometer devices.

Summary

This problem is addressed by a disposable protective cover for a hand-held spectrometer de vice, by a hand-held spectrometer system, by a use of the hand-held spectrometer system, by a method for protecting a hand-held spectrometer device and by a method for spectroscopic analysis of at least one sample, with the features of the independent claims. Advantageous em bodiments which might be realized in an isolated fashion or in any arbitrary combinations are listed in the dependent claims.

As used in the following, 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 situa tion 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 indi cating 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. In the following, in most cases, when referring to the respective feature or element, the expressions“at least one” or“one or more” will not be repeated, non-withstanding the fact that the respective feature or element may be present once or more than once.

Further, as used in the following, the terms "preferably", "more preferably", "particularly", "more particularly", "specifically", "more specifically" or similar terms are used in conjunction with op tional 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 fea tures. Similarly, features introduced by "in an embodiment of the invention" or similar expres sions are intended to be optional features, without any restriction regarding alternative embodi ments 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.

In a first aspect of the present invention, a disposable protective cover for a hand-held spec trometer device is disclosed. The term“protective cover” 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 limita tion, to an element or device which is configured for providing package, envelope or protection for another device, specifically from one or more of mechanical influences, chemical influences, dirt, dust or humidity. Specifically, as will be outlined in further detail below, the protective cover may comprise a rim, such as a circumferential rim. This circumferential rim, as an example, may be designed and/or configured as a circumferential sealing element, such as at least one cir cumferential sealing frame, configured for tightly engaging with the device to be covered. The protective cover may further comprise at least one flat or curved protective surface extending inside the rim, such as the circumferential sealing element. Thus, as an example, the protective cover may comprise one or more of a protective cap or a protective lid, such as a rigid cap or lid or a flexible cap or lid.

The term“disposable” as used herein is a broad term and is to be given its ordinary and cus tomary 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 property of an element or a device being designed for single use, specifically for being disposed of or being recycled after use. Specifically, the term disposable may refer to the fact that the element being disposable is manufactured by using cost-efficient manufacturing processes and/or cost- efficient materials. As an example, the disposable protective cover may fully or partially be made of a plastic material and/or may fully or partially be made by using mass-manufacturing techniques such as injection molding. The term“spectrometer device” 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 device capable of optically ana lyzing at least one sample, thereby generating at least one item of information on at least one spectral property of the sample. Specifically, the term may refer to a device which is capable of recording the signal intensity with respect to the corresponding wavelength of a spectrum or a partition thereof, such as a wavelength interval, wherein the signal intensity may, preferably, be provided as an electrical signal which may be used for further evaluation.

The term“hand-held” 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 property of a device capable of being moved by a human user, specifically capable of being carried by a human user, specifically ca pable of being carried by a human user with a single hand. Specifically, the hand-held device may be dimensioned for being carried by the human user, e.g. by having extensions in any di mension not exceeding 500 mm, specifically not exceeding 400 mm. Additionally or alternative ly, the hand-held device, for being carried by the human user, may have a weight not exceeding 5 kg, specifically not exceeding 3 kg or even not exceeding 1 kg.

The disposable protective cover comprises:

a front shield having at least one optical window element configured for transmitting light from at least one sample to the hand-held spectrometer device, and a rim protruding from the front shield for engagement with a housing of the hand held spectrometer device.

The term“front shield” 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 element of the protective cover which, when the protective cover is mounted to the hand-held spectrometer device, faces the sample to be analyzed by the hand-held spectrometer device. The front shield specifically may com prise at least one flat or curved surface which, as an example, extends within a frame provided by the disposable protective cover, such as within the above-mentioned sealing frame. The front shield specifically may have the shape of a flat disk, specifically allowing for bringing a sample in close proximity with the hand-held spectrometer device. Other shapes, however, are feasible.

The term“optical window element” 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 spe cial or customized meaning. The term specifically may refer, without limitation, to an element, such as a solid or flexible element, which is fully or partially transparent for light in one or more of the visible spectral range of 380 nm to 780 nm, the infrared spectral range of 780 nm to 1 mm, specifically the near-infrared spectral range of 0.78 pm to 3.0 pm, and the ultraviolet spec tral range of 100 nm to 380 nm. More specifically, as will be outlined in further detail below, the element may be fully or partially transparent, at least, for light in the spectral range of 1400 nm to 2000 nm. The term“transparent”, as used therein, specifically may refer to a transparency of at least 10%, more specifically of at least 50%, more specifically of at least 80%, as will be out lined in further detail below.

As outlined above, the optical window element is configured for transmitting light from at least one sample to the hand-held spectrometer device. Specifically, the optical window element when the disposable protective cover is mounted to and engaged with the hand-held spectrom eter device, is positioned such that light from a sample in front of the hand-held spectrometer device may pass through the optical window element into the hand-held spectrometer device, such as to at least one wavelength-selective element of the hand-held spectrometer device and/or to at least one detector device of the hand-held spectrometer device.

The disposable protective cover further comprises, as outlined above, at least one rim protrud ing from the front shield for engagement with a housing of the hand-held spectrometer device. The term“rim” is a broad term and is to be given its ordinary and customary meaning to a per son 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 element fully or partially surrounding another element, thereby providing a frame to the at least one other element and/or thereby providing for at least one edge of the at least one other element. Specifically, as outlined above, the at least one rim may form and/or comprise at least one sealing element, such as at least one cir cumferential sealing element, such as at least one circumferential sealing frame.

The rim is configured for engagement with a housing of the hand-held spectrometer device. The term“housing” is a broad term and is to be given its ordinary and customary meaning to a per son 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 element or a combination of elements which are configured for fully or partially surrounding and/or providing mechanical cover for one or more other elements. Thus, as an example, the housing may be or may comprise at least one rigid housing, such as at least one rigid housing made of at least one of a plastic material or a metal. The rim specifically may be configured for engagement with the housing by one or more of a form-fit connection, a force-fit connection or a connection by material engagement. Thus, as an example, as will be outlined in further detail below, the rim may be or may provide one or more connection elements and/or may provide for a flexible frame and/or sealing frame which may fully or partially surround a front surface of the hand-held spectrometer device.

The optical window element is made of at least one plastic material. Thus, the optical window element may fully or partially be made of at least one of a thermoplastic material and a duromer. The optical window element further has a transmittance of at least 80% over the spectral range of 1400 nm to 2000 nm. The term“transmittance” 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 spe cial or customized meaning. The term specifically may refer, without limitation, to a ratio T=l/lo, usually indicated in %, i.e. T [%] = l/lo 100%, of an intensity I of a light beam after passing through the optical window element and an intensity lo of the same light beam before passing through the optical window element, specifically in an experimental setup in which the light beam centrally and perpendicularly passes through the optical window element. In other words, the transmittance may be at least 80% for a monochromatic light beam having an arbitrary wavelength within the spectral range of 1400 nm to 2000 nm or for a light beam having a com position of wavelengths within the spectral range of 1400 nm to 2000 nm.

The optical window element may be embodied in various ways. Thus, the optical window ele ment may be made as a rigid transparent element, such as a rigid transparent disk or rigid transparent lens. Alternatively, however, the optical window element may also be fully or partial ly flexible. Thus, the optical window element specifically may be made of a flexible foil. Thus, as an example, the front shield may comprise a rigid frame having at least one window opening, and the optical window element may be disposed within the window opening. As an example, the foil may be adhered and/or embedded on one side or on both sides to the rigid frame, thereby covering the at least one window opening. Additionally or alternatively, a rim of the foil may also fully or partially be embedded into the rigid frame, such as by using injection molding techniques for integrating the foil with the rigid frame. In any case, the transparent foil forming the optical window element may fully or partially cover the window opening.

The front shield, specifically the optical window element, may generally have an arbitrary shape, depending on the specific application the hand-held spectrometer device is to be used for. Spe cifically, however, the front shield may fully or partially be designed as a flat element or having one or more flat surfaces. Thus, using one or more flat surfaces, the sample may be brought very close to the hand-held spectrometer device, thereby reducing losses of light, specifically of infrared light.

The rim may protrude from the front shield by at least 10 mm, more specifically by 10 mm to 50 mm. Thus, as an example, the front shield may form a flat disk, and the rim may protrude es sentially perpendicularly from the front shield, e.g. at an angle of 70° to 1 10°, by at least 10 mm. Other examples, however, are feasible.

As outlined above, the optical window element has a transmittance of at least 80% over the spectral range of 1400 nm to 2000 nm. Specifically, the transmittance of the optical window el ement may be at least 90% over the spectral range of 1300 nm to 2500 nm. Additionally or al ternatively, as outlined above, the transmittance of the optical window element may be at least 80% for every wavelength in the spectral range of 1400 nm to 2000 nm, specifically for every wavelength in the spectral range of 1300 nm to 2500 nm.

As outlined above, the disposable protective cover may be engaged with the hand-held spec trometer device by one or more of a force-fit connection, a form-fit connection or a connection by material engagement. Specifically, the front shield may have at least one adhesive surface for adhesive engagement with a front surface of the hand-held spectrometer device. Thus, as an example, the adhesive surface may fully or partially surround the optical window element of the front shield. As an example, the adhesive surface may be or may comprise an adhesive ring, e.g. having a round, oval, rectangular or polygonal shape, the adhesive ring surrounding the optical window element of the front shield. Thereby, in addition or as an alternative to one or more optional other connection elements comprised by the disposable protective cover for the purpose of connecting the disposable protective cover with the hand-held spectrometer device, the disposable protective cover may be adhered to the front surface of the hand-held spectro meter device, specifically reversibly.

As outlined above, the optical window element specifically may be made of a thin material, such as a foil or a thin rigid transparent element. Thus, the optical window element specifically may have a thickness of 4 pm to 100 pm, specifically a thickness of 5 pm to 50 pm, more specifically a thickness of 6 pm to 25 pm. By reducing the thickness of the optical window element, the ab sorption or diffusion losses in the material of the optical window element may be reduced, spe cifically in the infrared spectral range, as will be shown in further detail below.

As it turns out and as will be shown in further detail below, designing the optical window ele ment with a thickness as outlined above, the spectral transmission properties, specifically in the infrared spectral range, may be influenced by interference effects. Therefore, specifically in or der to avoid interference effects, the plastic material of the optical window element may have at least one roughened surface for suppression of interference patterns, specifically a roughened surface having an RMS roughness of 0,5 pm to 10 pm. Additionally or alternatively, also for the purpose of suppression of interference patterns, the optical window element may have an anti- reflective coating. Additionally or alternatively, the plastic material of the optical window element may be chosen to have a refractive index close to the sample medium, e.g. a refractive index deviating by no more than 0.1 from the refractive index of the sample to be analyzed. As an example, specifically for aqueous media, the plastic material of the optical window element may be chosen to have a refractive index close to water, e.g. having a refractive index of 1.33 ± 0.1. As an example, PTFE has a refractive index of 1.36 which is close to the refractive index of wa ter of 1.33. Hence, PTFE may be a suitable material for measuring samples with a high water content.

The plastic material of the optical window element specifically may be selected such that the absorption losses are low. Specifically, the plastic material of the optical window element may comprise at least one plastic material selected from the group consisting of: a polyolefin, specif ically polypropylene or polyethylene; a polyester, specifically polyethylene terephthalate; a fluor- inated polymer, specifically polytetrafluoroethylene; a chlorinated polymer, specifically polyvi nylchloride; a polystyrene; a polyamide, specifically PA6; a polyacrylate, specifically poly(methyl methacrylate). Thereof, as will be outlined in further detail below, specifically fluorinated poly mers turn out to be highly transparent in the infrared spectral range, specifically in the above- mentioned spectral range and, thus, may be used for optical window elements which are highly transparent and, still, provide sufficient thickness for stability. The disposable protective cover specifically may be bio-degradable. Thus, the disposable pro tective cover specifically may be made of at least one material which is degradable by itself and/or in conjunction with appropriate microorganisms. The disposable protective cover specifi cally may be configured such that the disposable protective cover may be disposable over the regular waste system and/or even via the sewage system, such as the regular municipal sew age system.

In a further aspect of the present invention, a hand-held spectrometer system is disclosed. The term“spectrometer system” is a broad term and is to be given its ordinary and customary mean ing 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 system having at least two in teracting components, wherein at least one of these interacting components is a spectrometer device. For the definition of the term“hand-held”, reference may also be made to the description of the spectrometer device given above.

The hand-held spectrometer system comprises:

i. at least one hand-held spectrometer device configured for analyzing light from at least one sample, the hand-held spectrometer device comprising:

- at least one housing having at least one entrance window;

- at least one wavelength-selective element configured for separating incident light in to a spectrum of constituent wavelengths, the wavelength-selective element being disposed within the housing;

- at least one detector device configured for detecting at least a portion of the constit uent wavelengths, the detector device being disposed within the housing; and ii. at least one disposable protective cover according to the present invention, such as according to any one of the above-mentioned embodiments and/or according to any one of the embodiments disclosed in further detail below.

The term“analyzing” 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 process of deriving at least one item of information on a property of a sample. Specifically, the hand-held spectrometer device may be configured for deriving at least one item of information on at least one spectral property of the sample. As an example, the hand-held spectrometer device may be configured for deriving at least one item of spectral information on the sample, such as at least one distribution of intensi ties over a spectral range for a reflection spectrum and/or for a transmission spectrum. Other examples, however, are possible. The hand-held spectrometer device specifically may be con figured for providing at least one item of electronic information, such as an analogue and/or digi tal signal, representative for the at least one item of spectral information.

The term“sample” 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 arbitrary amount of material, an element or a device to be analyzed. Specifically, the sample may be an amount of amorphous material, such as an amount of one or more of liquid, powder, pellets, particles or gas. Specific examples of samples will be given in further detail below.

The term“entrance window” 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 arbitrary element or opening of the hand-held spectrometer device allowing for the light entering the housing. Thus, as an example, the entrance window may be or may comprise an opening in the housing. The open ing may be empty or may comprise one or more transparent elements, such as one or more transparent elements selected from the group consisting of glass elements or plastic elements.

The term“wavelength-selective element” is a broad term and is to be given its ordinary and cus tomary 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 arbitrary element or a combination of elements suitable for one or more of transmitting, reflecting, deflecting or scattering light in a wavelength-dependent manner. The wavelength-selective element, as an example, may be or may comprise at least one element selected from the group consisting of: an optical grating; an optical prism; a wavelength selective optical filter, specifically a length variable filter.

The term“detector device” is a broad term and is to be given its ordinary and customary mean ing 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 arbitrary device or combina tion of devices capable of monitoring and/or recording at least one physical, chemical or biologi cal parameter. Specifically, the detector device may comprise at least one optical detector de vice, such as a device configured for recording and/or monitoring incident light. The detector device specifically may, thus, be or may comprise an optical detector element, such as at least one optical sensor, e.g. an optical semiconductor sensor. As an example, the detector device may comprise at least one photodetector such as at least one CCD or CMOS device. The de tector device specifically may comprise at least one detector array comprising a plurality of pixe- lated sensors, wherein each of the pixelated sensors is configured to detect at least a portion of at least one of the constituent wavelengths.

The hand-held spectrometer system, as outlined above, comprises at least one disposable pro tective cover according to the present invention, such as according to any one of the above- mentioned embodiments and/or according to any one of the embodiments disclosed in further detail below. The at least one disposable protective cover may be reversibly connectable to the hand-held spectrometer device. Specifically, a plurality of disposable protective covers may be comprised by a kit, and, e.g. after each analysis by using the hand-held spectrometer system, the disposable protective cover may be replaced by a new disposable protective cover. The optical window element of the hand-held spectrometer system, when the rim of the dispos able protective cover is engaged with the housing of the hand-held spectrometer device, specif ically may be disposed in front of the entrance window of the hand-held spectrometer device. Specifically, the entrance window of the hand-held spectrometer system may be disposed at a distance from the entrance window of the hand-held spectrometer device of no more than 5 mm, specifically of no more than 2 mm and more specifically of no more than 1 mm.

The hand-held spectrometer system specifically may comprise at least one detector array, the detector array comprising a plurality of pixelated sensors. Each of the pixelated sensors may be configured to detect at least a portion of at least one of the constituent wavelengths. Thus, as an example, by using the wavelength-selective element, incident light may be split into two or more spectral components, and the pixels forming the pixelated sensors of the detector array may be assigned to one or more of the spectral components.

The wavelength-selective element may comprise at least one element selected from the group consisting of: an optical grating; an optical prism; a wavelength selective optical filter, specifical ly a length variable filter. Other wavelength-selective elements are generally known to the skilled person and may be applied in the present hand-held spectrometer device, too.

The entrance window of the spectrometer device specifically may comprise at least one trans parent element, specifically at least one optical lens. Thus, as an example and as outlined above, the entrance window may comprise at least one opening in the housing, and the at least one opening may fully or partially be covered with at least one transparent element, such as at least one optical lens and/or at least one transparent disk or foil.

The hand-held spectrometer device may further comprise at least one optical element config ured for receiving incident light from a sample and transferring the incident light to the wave- length-selective element. Thus, the transfer of the incident light may take place by one or more of waveguiding, reflection, refraction, focusing or defocusing. Consequently, the at least one optical element, as an example, may comprise one or more of an optical waveguide, a reflective element such as a mirror, a refractive element such as a lens or a focusing or defocusing mirror.

As an example, the optical element may comprise at least one optical concentrator device. Therein, the term“optical concentrator device” specifically may refer to a non-imaging optical element having an input, also denoted as“entrance pupil” or“entrance aperture”, an output lo cated oppositely to the input, wherein the output may also be denoted by one of the terms“exit pupil” or“exit aperture”, and an optically guiding structure located between the input and the output, wherein the optical concentrator device may be, in normal direction of operation, adapted for capturing light at the input at a large angular spread, concentrating the captured light within the optically guiding structure, and emitting the concentrated light at the output. By way of example, the optical concentrator may, therefore, be used in concentrated photovoltaics in order to allow high solar concentration under large possible entrance angles. In the present handheld spectrometer device, the optical concentrator device specifically may be operated in reverse direction. More specifically, the optical concentrator device may have a non-conical shape. The non-conical shape specifically may comprise a shape selected from the group con sisting of: a parabolic shape and an elliptical shape. The optical concentrator device may have at least two sidewalls which are adapted for reflecting incident light.

The hand-held spectrometer device may further comprise an illumination source configured for illuminating the sample. The illumination source specifically may comprise at least one element selected from the group consisting of: an LED, a laser, an incandescent lamp. The at least one illumination source, also referred to as a light source, may fully or partially be located inside the housing of the hand-held spectrometer device and/or may fully or partially be located outside the housing of the hand-held spectrometer device and/or may also be fully or partially integrated into the housing of the hand-held spectrometer device. In case the at least one illumination source is located inside the housing, the illumination of the sample may fully or partially take place through the entrance window of the housing and/or may fully or partially take place through at least one separate illumination opening.

The illumination source may fully or partially be integrated with remaining parts of the hand-held spectrometer device, such as with the housing. The illumination source may, however, also be fully or partially be separate from remaining parts of the hand-held spectrometer device, such as by providing a separate illumination source which is spatially separated from the housing and may be handled independently.

The disposable protective cover, when the rim is engaged with the housing of the hand-held spectrometer device, may be configured for also covering the illumination source. The hand held spectrometer system may be configured for allowing for an illumination of the sample through the front shield, specifically through the optical entrance window. The disposable pro tective cover, however, may also comprise at least one separate illumination window separate from the optical entrance window, allowing for an illumination of the sample through the front shield.

The hand-held spectrometer system may further comprise at least one evaluation unit config ured for determining information related to at least one spectral property of the sample by eval uating at least one detector signal provided by the detector device. The evaluation unit, as an example, may comprise at least one processor configured for performing the evaluation of the detector signal. The evaluation unit, as an example, may fully or partially be disposed within the housing and/or may fully or partially be disposed outside the housing. The evaluation unit may be integrated into the spectrometer device or may be separate from the spectrometer device, such as by being connected to the spectrometer device via at least one wire-bound or wireless interface.

In a further aspect of the present invention, the use of the hand-held spectrometer system ac cording to the present invention, such as according to any one of the embodiments disclosed above and/or according to any one of the embodiments disclosed in further detail below, is pro- posed, for a purpose of use, selected from the group consisting of: an infrared detection appli cation; a heat-detection application; a heat-seeking application; a flame-detection application; a fire-detection application; a spectroscopy application; an exhaust gas monitoring application; a combustion process monitoring application; a pollution monitoring application; an industrial pro cess monitoring application; a chemical process monitoring application; a food processing pro cess monitoring application; a water quality monitoring application; an air quality monitoring ap plication; a quality control application; a motion control application; an exhaust control applica tion; a gas sensing application; a gas analytics application; a motion sensing application; a chemical sensing application.

In a further aspect of the present invention, a method for protecting the hand-held spectrometer device in the hand-held spectrometer system according to the present invention, such as ac cording to any one of the embodiments disclosed above and/or according to any one of the em bodiments disclosed in further detail below, is proposed. The method comprises the following method steps. The method steps may be performed in the given order. A different order is also possible, including the option of performing one or more of the method steps fully or partially simultaneously. Further, one or more of the method steps may be performed in a repeated fash ion. The method may comprise additional steps which are not listed. The method comprises the following steps:

a) providing the hand-held spectrometer device;

b) providing the disposable protective cover; and

c) engaging the rim of the disposable protective cover with the housing of the hand held spectrometer device, such that the optical window element is disposed in front of the entrance window of the hand-held spectrometer device.

Method step c) may simply comprise plugging the disposable protective cover onto the hand held spectrometer device, such as by one or more of a form-fit or force-fit connection.

In a further aspect of the present invention, a method for spectroscopic analysis of at least one sample, specifically at least one liquid sample, is disclosed. The method comprises the following method steps. The method steps may be performed in the given order. A different order is also possible, including the option of performing one or more of the method steps fully or partially simultaneously. Further, one or more of the method steps may be performed in a repeated fash ion. The method may comprise additional steps which are not listed. The method comprises the following steps:

I. providing the hand-held spectrometer system according to any one of the preceding claims referring to a hand-held spectrometer system;

II. engaging the rim of the disposable protective cover of the hand-held spectrometer system with the housing of the hand-held spectrometer device of the hand-held spectrometer system;

III. bringing the front shield of the disposable protective cover in contact with the sam ple; and IV. evaluating at least one detector signal provided by the detector device of the hand held spectrometer device.

The evaluation of the at least one detector signal provided by the detector device may take place in various ways. Thus, as an example, the evaluation may comprise deriving at least one item of information on at least one spectroscopic property of the sample, such as at least one item of analogue information and/or at least one item of digital information. As an example, the evaluation may comprise seeding at least one detector signal provided by the detector device, such as at least one analogue signal and/or at least one digital signal, into at least one evalua tion unit of the hand-held spectrometer system and/or of the hand-held spectrometer device and processing this at least one detector signal electronically. The processing, as an example, may comprise one or more steps, such as one or more preprocessing steps, e.g. filtering, averaging or the like. Further, the processing may comprise one or more further processing steps, e.g. generating the at least one item of spectroscopic information, e.g. by using one or more conver sion algorithms. The evaluation may further comprise an output of information to at least one user and/or to at least one other device, e.g. one or more of a visual output by using a display device, and audible output by using a loudspeaker, or an haptic output by using vibrations or the like, and/or an electronic output via at least one wireless and/or at least one wire-bound inter face. The evaluation unit may comprise one or more user interfaces and/or one or more elec tronic interfaces.

The devices and methods according to the present invention provide a large number of ad vantages over devices and methods of similar kind as known in the art. Thus, the disposable protective cover, the hand-held spectrometer system and the methods according to the present invention allow for a precise and reproducible application of spectrometry in the field, by over coming the above-mentioned challenges with respect to the contamination of sensitive parts of the spectrometer device.

Specifically, the hand-held spectrometer system and, more specifically, the disposable protec tive cover may get in direct contact with the sample to be analyzed, thereby providing for repro ducible spectroscopic measurement conditions in the field. Thus, a well-defined and short dis tance between the sample and the spectrometer device may be provided by directly getting the disposable protective cover in contact with the sample.

Thereby, hand-held spectrometers may be used in various fields of application, from industrial to consumer applications. During measurement, a measurement head of the spectrometer sys tem may get in touch with the sample. Thus, contaminating samples like olive oil or other chem icals which, typically, might contaminate the spectrometer device, may be analyzed. Further, even poisonous or inflammable samples may be analyzed, by simply discarding the disposable protective cover after analysis. Thus, safety issues may be avoided. The disposable protective cover, still, may be tailor-made with respect to its optical properties, specifically by rendering at least part of the disposable protective cover transparent for the required spectral range, specifi cally the infrared spectral range. The disposable protective cover, on the other hand, may be manufactured in a rather cost- efficient way. Thus, specifically, mass-manufacturing techniques may be used, such as molding techniques or deep-drawing techniques. The disposable protective cover may be discarded af ter one or several measurements and may be replaced by a new disposable protective cover for further measurements.

Summarizing and without excluding further possible embodiments, the following embodiments may be envisaged:

Embodiment 1 : A disposable protective cover, specifically for use in a hand-held spectrometer device or in a hand-held spectrometer system and/or for use with a hand-held spectrometer device, comprising:

a front shield having at least one optical window element configured for transmitting light from at least one sample to the hand-held spectrometer device, and a rim protruding from the front shield for engagement with a housing of the hand held spectrometer device,

wherein the optical window element is made of at least one plastic material, wherein the optical window element further has a transmittance of at least 80% over the spectral range of 1400 nm to 2000 nm.

Embodiment 2: The disposable protective cover according to the preceding embodiment, wherein the optical window element is fully or partially flexible, specifically made of a flexible foil.

Embodiment 3: The disposable protective cover according to the preceding embodiment, wherein the front shield comprises a rigid frame having a window opening, wherein the optical window element is disposed within the window opening.

Embodiment 4: The disposable protective cover according to any one of the preceding embod iments, wherein the front shield, specifically the optical window element, is fully or partially flat.

Embodiment 5: The disposable protective cover according to any one of the preceding embod iments, wherein the rim protrudes from the front shield by at least 10 mm, more specifically by 10 mm to 50 mm.

Embodiment 6: The disposable protective cover according to any one of the preceding embod iments, wherein the transmittance of the optical window element is at least 90% over the spec tral range of 1300 nm to 2500 nm.

Embodiment 7: The disposable protective cover according to any one of the preceding embod iments, wherein the transmittance of the optical window element is at least 80% for every wave length in the spectral range of 1400 nm to 2000 nm. Embodiment 8: The disposable protective cover according to any one of the preceding embod iments, wherein the front shield has at least one adhesive surface for adhesive engagement with a front surface of the hand-held spectrometer device.

Embodiment 9: The disposable protective cover according to the preceding embodiment, wherein the adhesive surface fully or partially surrounds the optical window element of the front shield.

Embodiment 10: The disposable protective cover according to any one of the preceding embod iments, wherein the optical window element has a thickness of 4 pm to 150 pm, specifically a thickness of 5 pm to 100 pm, more specifically a thickness of 6 pm to 50 pm.

Embodiment 1 1 : The disposable protective cover according to any one of the preceding embod iments, wherein the plastic material of the optical window element comprises at least one plastic material selected from the group consisting of: a polyolefin, specifically polypropylene or poly ethylene; a polyester, specifically polyethylene terephthalate; a fluorinated polymer, specifically polytetrafluoroethylene; a chlorinated polymer, specifically polyvinylchloride; a polystyrene; a polyamide, specifically PA6; a polyacrylate, specifically poly(methyl methacrylate).

Embodiment 12: The disposable protective cover according to any one of the preceding embod iments, wherein the plastic material of the optical window element has at least one roughened surface for suppression of interference patterns, specifically a roughened surface having an RMS roughness of 0,5 pm to 10 pm.

Embodiment 13: The disposable protective cover according to any one of the preceding embod iments, wherein the optical window element has an anti-reflective coating.

Embodiment 14: The disposable protective cover according to any one of the preceding embod iments, wherein the front shield has the shape of a flat disk.

Embodiment 15: The disposable protective cover according to any one of the preceding embod iments, wherein the disposable protective cover is bio-degradable.

Embodiment 16: A hand-held spectrometer system, comprising:

i.at least one hand-held spectrometer device configured for analyzing light from at least one sample, the hand-held spectrometer device comprising:

- at least one housing having at least one entrance window;

- at least one wavelength-selective element configured for separating incident light in to a spectrum of constituent wavelengths, the wavelength-selective element being disposed within the housing;

- at least one detector device configured for detecting at least a portion of the constit uent wavelengths, the detector device being disposed within the housing; and ii.at least one disposable protective cover according to any one of the preceding embodi ments.

Embodiment 17: The hand-held spectrometer system according to the preceding embodiment, wherein the optical window element, when the rim of the disposable protective cover is engaged with the housing of the hand-held spectrometer device, is disposed in front of the entrance win dow of the hand-held spectrometer device.

Embodiment 18: The hand-held spectrometer system according to the preceding embodiment, wherein the entrance window of the hand-held spectrometer system is disposed at a distance from the entrance window of the hand-held spectrometer device of no more than 5 mm, specifi cally of no more than 2 mm and more specifically of no more than 1 mm.

Embodiment 19: The hand-held spectrometer system according to any one of the preceding embodiments referring to a hand-held spectrometer system, wherein the detector device com prises at least one detector array comprising a plurality of pixelated sensors, wherein each of the pixelated sensors is configured to detect at least a portion of at least one of the constituent wavelengths.

Embodiment 20: The hand-held spectrometer system according to any one of the preceding embodiments referring to a hand-held spectrometer system, wherein the wavelength-selective element comprises at least one element selected from the group consisting of: an optical grat ing; an optical prism; a wavelength selective optical filter, specifically a length variable filter.

Embodiment 21 : The hand-held spectrometer system according to any one of the preceding embodiments referring to a hand-held spectrometer system, wherein the entrance window of the spectrometer device comprises at least one transparent element, specifically at least one optical lens.

Embodiment 22: The hand-held spectrometer system according to any one of the preceding embodiments referring to a hand-held spectrometer system, wherein the hand-held spectrome ter device further comprises at least one optical element configured for receiving incident light from a sample and transferring the incident light to the wavelength-selective element.

Embodiment 23: The hand-held spectrometer system according to the preceding embodiment, wherein the optical element comprises at least one optical concentrator device, wherein the optical concentrator device specifically is operated in reverse direction.

Embodiment 24: The hand-held spectrometer system according to the preceding embodiment, wherein the optical concentrator device has a non-conical shape. Embodiment 25: The hand-held spectrometer system according to the preceding embodiment, wherein the non-conical shape comprises a shape selected from the group consisting of: a pa rabolic shape and an elliptical shape.

Embodiment 26: The hand-held spectrometer system according to any one of the three preced ing embodiments, wherein the optical concentrator device has at least two sidewalls which are adapted for reflecting incident light.

Embodiment 27: The hand-held spectrometer system according to any one of the preceding embodiments referring to a hand-held spectrometer system, wherein the hand-held spectrome ter device further comprises an illumination source configured for illuminating the sample.

Embodiment 28: The hand-held spectrometer system according to the preceding embodiment, wherein the illumination source comprises at least one element selected from the group consist ing of: an LED, a laser, an incandescent lamp.

Embodiment 29: The hand-held spectrometer system according to any one of the two preceding embodiments, wherein the disposable protective cover, when the rim is engaged with the hous ing of the hand-held spectrometer device, is configured for covering the illumination source, wherein the hand-held spectrometer system is configured for allowing for an illumination of the sample through the front shield, specifically through the optical entrance window.

Embodiment 30: The hand-held spectrometer system according to any one of the preceding embodiments referring to a hand-held spectrometer system, further comprising at least one evaluation unit configured for determining information related to at least one spectral property of the sample by evaluating at least one detector signal provided by the detector device.

Embodiment 31 : A use of the hand-held spectrometer system according to any one of the pre ceding embodiments referring to a hand-held spectrometer system, for a purpose of use, se lected from the group consisting of: an infrared detection application; a heat-detection applica tion; a heat-seeking application; a flame-detection application; a fire-detection application; a smoke-detection application; a spectroscopy application; an exhaust gas monitoring application; a combustion process monitoring application; a pollution monitoring application; an industrial process monitoring application; a chemical process monitoring application; a food processing process monitoring application; a water quality monitoring application; an air quality monitoring application; a quality control application; a motion control application; an exhaust control appli cation; a gas sensing application; a gas analytics application; a motion sensing application; a chemical sensing application.

Embodiment 32: A method for protecting the hand-held spectrometer device in the hand-held spectrometer system according to any one of the preceding embodiments referring to a hand held spectrometer system, the method comprising:

a) providing the hand-held spectrometer device; b) providing the disposable protective cover; and

c) engaging the rim of the disposable protective cover with the housing of the hand held spectrometer device, such that the optical window element is disposed in front of the entrance window of the hand-held spectrometer device.

Embodiment 33: A method for spectroscopic analysis of at least one sample, specifically at least one liquid sample, the method comprising:

I. providing the hand-held spectrometer system according to any one of the preceding em bodiments referring to a hand-held spectrometer system;

I I. engaging the rim of the disposable protective cover of the hand-held spectrometer system with the housing of the hand-held spectrometer device of the hand-held spectrome ter system;

I I I. bringing the front shield of the disposable protective cover in contact with the sample; and

IV. evaluating at least one detector signal provided by the detector device of the hand-held spectrometer device.

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 restrict ed by the preferred embodiments. The embodiments are schematically depicted in the Figures. Therein, identical reference numbers in these Figures refer to identical or functionally compara ble elements.

In the Figures:

Figure 1 shows an exemplary embodiment of a hand-held spectrometer system comprising a hand-held spectrometer device and a disposable protective cover; and

Figures 2 to 4 show absorbance curves of various plastic materials.

Detailed description of the embodiments

In Fig. 1 , an exemplary embodiment of a hand-held spectrometer system 1 10 is shown in a cross-sectional view. The hand-held spectrometer system 1 10 comprises, in this embodiment, an exemplary embodiment of a hand-held spectrometer device 1 12 as well as an exemplary embodiment of a disposable protective cover 1 14 for the hand-held spectrometer device 1 12. The hand-held spectrometer system 1 10 is configured for analyzing a sample 1 16, which is schematically shown in the Figure and which, as an example, may be a liquid sample. In the setup of Fig. 1 , the hand-held spectrometer system 1 10 is in physical contact with the sample 1 16, e.g. by getting the disposable protective cover 1 14 in direct contact with the sample 1 16, such as by dipping the disposable protective cover 1 14 into the sample 1 16.

The hand-held spectrometer device 1 12 comprises, in the embodiment shown, a housing 1 18, the housing 1 18 having at least one entrance window 120. The hand-held spectrometer device 1 12 further comprises, disposed within the housing 1 18, at least one wavelength selective ele ment 122 configured for separating incident light 124 into a spectrum of constituent wave lengths. The hand-held spectrometer device 1 12 further comprises, also disposed within the housing 1 18, at least one detector device 126 configured for detecting at least a portion of the constituent wavelengths. The hand-held spectrometer device 1 12 may further comprise at least one evaluation unit 128, e.g. an evaluation unit having at least one processor, wherein the eval uation unit 128, as an example, may be configured for evaluating detector signals of the at least one detector device 126. The evaluation unit 128 may further be configured for fulfilling other tasks, such as controlling one or more illumination sources 130.

Thus, as an example, the hand-held spectrometer device 1 12 may further comprise one or more illumination sources 130 which may be controlled by the evaluation unit 128. The one or more illumination sources 130 may be disposed within the housing 1 18 and/or outside the hous ing 1 18. The at least one illumination source 130 may be positioned to illuminate the sample 1 16 with illumination light 132, which may, as an example, be one or more of reflected, transmit ted, scattered or absorbed by the sample 1 16 and/or parts thereof. It shall be noted that the hand-held spectrometer device 1 12 may also be designed without illumination source 130, e.g. by using other means, such as other light sources, for illuminating and/or exciting the sample 1 16. Thus, as an example, an electrical stimulation of the sample 1 16 may also take place, or the sample 1 16 may e.g. be a fluorescent or chemiluminescent sample.

As outlined above, the hand-held spectrometer system 1 10 further comprises the at least one disposable protective cover 1 14. The disposable protective cover 1 14 comprises a front shield 134, wherein the front shield 134 may provide for a frame 136. Within the front shield 134, spe cifically within the frame 136, at least one optical window element 138 is provided. The optical window element 138 specifically may be made of at least one plastic material and may have a thickness of 3 pm to 1 mm. The optical window element 138 is made of an optically transparent material, such as of an optically transparent plastic material. The optical window element 138 has a transmittance of at least 99% over the spectral range of 1 100 nm to 2500 nm.

More specifically, the optical window element 138 may be made of one or more plastic materials selected from the group consisting of: a polyolefin, specifically polypropylene or polyethylene; a polyester, specifically polyethylene terephthalate; a fluorinated polymer, specifically polytetraflu- oroethylene; a chlorinated polymer, specifically polyvinylchloride; a polystyrene; a polyamide, specifically PA6; a polyacrylate, specifically poly(methyl methacrylate). Specifically, the optical window element 138 may be made of PTFE having a thickness of 6 pm to 125 pm, such as hav ing a thickness of 25 pm to 100 pm. The optical window element 138, as an example, may be made as a flexible foil which is connected to the frame 136, thereby allowing for a low thickness of the optical window element 138. The frame 136 specifically may be a rigid frame, providing for mechanical stability for the optical window element 136 which, consequently, may be rather thin. Thus, the frame 136 may have a window opening 140, wherein the optical window element 138 is disposed within the window opening 140.

As can be seen in Fig. 1 , the front shield 134 may be designed in a flat fashion. The disposable protective cover 1 14 further comprises a rim 142 which protrudes from the front shield 134. Thus, the rim 142 may circumferentially enclose and/or surround the front shield 134 and may protrude from the front shield 134 e.g. perpendicularly. Thus, the rim 142 may have a tubular or cylindrical shape, with the front shield 134 closing one end of the tubular or cylindrical shape. Consequently, the front shield 134 and the rim 142 together may form a semi-opened cylinder, with a closed side of the semi-opened cylinder facing the sample 116, and the open end of the cylinder facing the hand-held spectrometer device 112. The flat shape of the front shield 134 may bring the optical window element 138 in close proximity to the entrance window 120 of the hand-held spectrometer device 112, thereby providing for short optical path lengths, which spe cifically are valuable in infrared spectrometry.

As can be seen in Fig. 1 , the rim 142 is configured for engaging with the housing 1 18 of the hand-held spectrometer device 112. Thus, the rim 142 specifically may be configured for sur rounding a front part of the housing 118, e.g. by forming a force-fit and/or a form-fit connection with the housing 1 18. As an example, the rim 142 may be designed in a flexible fashion, thereby allowing for overtighten the front portion of the housing 118 with the rim 142. The rim 142 may, as an example, protrude from the front shield 134 by at least 10 mm. The rim 142 may form a tight connection with the housing 118, thereby sealing a space in between the front shield 134 and the entrance window 120 from the surrounding environment, e.g. for preventing sample 116 entering this space. The rim 142 may further optionally comprise one or more connecting ele ments 144, such as one or more circumferential sealing lips.

The disposable protective cover 114 may further comprise additional elements. Thus, as an example, the disposable protective cover 114 may also fully or partially be adhered to the hous ing 118. For this purpose, the disposable protective cover 114 may comprise at least one adhe sive surface 146 for adhering the disposable protective cover 114 to the housing 118. Thereby, an additional sealing may be provided, e.g. for protecting the space between the optical window element 138 and the entrance window 120 from ingression of sample 1 16.

In Figures 2 to 4, absorption measurements of various plastic materials are shown, which may be used for the optical window element 138. Therein, besides the materials, the thickness of the plastic material is also varied. Each of the graphs in these Figures shows, on the horizontal ax is, the wave number k = l ¹ , given in cm ¹ . On the vertical axis, the dimensionless absorbance A is given, which is the negative decadic logarithm of the transmittance T as defined above, i.e. A=-logioT. For the sake of clarity and simplification, several wavelengths are marked on the horizontal axis, as well as specific transmittances on the vertical axis. In Fig. 2, absorbance curves for various materials having a similar thickness in the range of 23 miti to 30 miti are shown. Therein, PTFE denotes the fluorinated polymer polytetrafluoroethylene, PS denotes polystyrene, PET denotes polyethylene terephthalate, PELD denotes low density polyethylene, and PA6 denotes polycaprolactam, also referred to as Nylon 6.

Firstly, as can be seen, all of these materials are generally suited to fulfill the above-mentioned precondition of having a transmittance of at least 80% over the spectral range of 1400 nm to 2000 nm. For wavelengths above 2.0 pm, higher absorption peaks may be noted, which severe ly decrease transmission.

As can further be seen in these curves, the absorbance is subject to interference effects, which leads to periodic and sinusoidal absorbance curves as a function of the wave number. These interference effects are mainly due to the fact that the layer thickness is in the range of the wavelength and, at least partially, differs from the wavelength by no more than an order of mag nitude. These interference effects, when using the plastic materials for spectroscopic purposes, may either be corrected electronically or mathematically, e.g. by filtering these periodic signals. Additionally or alternatively, however, interference effects may be suppressed by optical means, such as by using a roughened surface for the optical window element 138 and/or by using anti reflection coatings on the optical window element.

As a further result of the curves shown in Fig. 2, it turns out that fluorinated polymers such as PTFE provide for high transparency of the optical window element 138. Thus, over the full spec tral range of 1.4 pm to 2.5 pm, which is of high interest for infrared spectroscopy, PTFE shows a transmittance of more than 95% for a layer thickness of 25 pm. Specifically, even in the range of 2.0 pm to 2.5 pm, in which the other polymers exhibit a clear absorption peak, PTFE has a high transmittance of more than 95%. Consequently, since PTFE is also known as a highly inert ma terial which is suited to sustain even aggressive sample materials, fluorinated polymers such as PTFE turn out to be well-suited candidate materials for the optical window element 138. Since PTFE has an absorbance of below 0.02, corresponding to a transmittance of more than 95%, and since the absorbance is roughly proportional to the thickness of the material, PTFE may even be used at a thickness of approximately 125 pm, by still having an absorbance of less than 0.1 , corresponding to a transmittance of more than 80%. Further, as outlined above, PTFE has a refractive index of 1.36 which is close to the refractive index of water of 1.33, thereby reducing losses at the sample interface.

In Fig. 3, thickness dependency of the absorbance is shown for polypropylene, denoted as PP, for thicknesses of 4 pm to 50 pm. According to the Beer-Lambert law, since the absorbance is a logarithmic figure, the absorbance should be roughly proportional to the thickness of the plastic material, which is approximately valid for these curves. These effects, however, are superim posed by other optical effects, such as the above-mentioned interference effects, effects of ma terial inhomogeneity or surface effects. Still, as can be seen, at least for thicknesses of approx imately up to 12 pm, polypropylene fulfills the above-mentioned criterion of transmittance of more than 80% in the wavelength range of 1.4 pm to 2.5 pm. In Fig. 4, finally, further materials are evaluated, including polypropylene, polycarbonate PC and high density polyethylene PEHD. As can be seen and as discussed above in the context of Fig. 3, polypropylene fulfills the above-mentioned requirements sufficiently. High density polyeth- ylene, however, fails to fulfill the requirements in the range of 2.2 pm to 2.5 pm, mainly due to a high absorption peak. Again and as discussed above, interference effects are detected which may require correction by electronic/mathematical means and/or by optical means.

List of reference numbers

110 hand-held spectrometer system 112 hand-held spectrometer device 114 disposable protective cover

116 sample

118 housing

120 entrance window

122 wavelength-selective element 124 light

126 detector device

128 evaluation unit

130 illumination source

132 illumination light

134 front shield

136 frame

138 optical window element 140 window opening

142 rim

144 connecting element

146 adhesive surface

References

US 2014/131578 A1

US 6,022,140