Technical Field

The invention relates to an optical spectroscopy device having a measurement chamber, a plurality of light emitter modules having differing center wavelengths arranged at said measurement chamber, and a plurality of light detector modules having different center wavelengths arranged at said measurement chamber. The invention also relates to a method for operating such a device.

Background Art In known optical spectrometers for the spectral detection or analysis of specific components in non-solid media, light emitters and light detectors are typically arranged in a single plane, with the sample under test placed between the light emitters and light detectors. For absorption spectroscopy, light detectors are typically arranged directly opposite the light emitters, whereas for spectroscopic techniques in- volving scattering, fluorescence, or phosphorescence light detectors may be arranged at various angles with respect to the light detectors.

US 6122042 describes an apparatus for photometric analysis and/or identification of properties of an object. It comprises a collection of light sources having distinct wavelength envelopes at that are activated in a rapid sequence of combi- nations. The apparatus further comprises a collection of spatially distributed light detectors. The light sources and detectors can be arranged in modules, with each module having its own light sources and detectors, and the modules may be arranged in a ring.

US 7046347 describes a colorimetric instrument with circular ar- rangements of light sources and light detectors. The light sources operate at different wavelengths, and electrical circuitry controls the switching between them.

Disclosure of the Invention The problem to be solved by the present intention is to provide an optical spectroscopy device of the type mentioned above and a method for operating it that have good measurement accuracy.

This problem is solved by the optical device and method of the independent claims.

Accordingly, in one aspect, the invention relates to an optical spectroscopy device comprising at least the following elements:

- A measurement chamber: This measurement chamber receives the fluid to be tested.

- A plurality of light emitter modules having differing center wavelengths arranged at said measurement chamber: These light emitter modules may be operated to emit light of different wavelengths.

- A plurality of light detector modules having different center wavelengths arranged at said measurement chamber: These light detector modules may be operated to sample light at different wavelengths after its interaction with the fluid.

The device further comprises at least a first set of emitter modules and detector modules having equal center wavelengths.

Advantageously, at least one set of emitter and detector modules is arranged with the detector and emitter modules facing each other on opposing sides of the measurement chamber within a cone of light of the emitter module.

In this context, “within a cone of light” advantageously designates any angular location at which the intensity (power per unit solid angle) of the emission of the emitter module is at least 50% of the maximum far-field intensity of the emitter module. Note: The cone of light may be laterally shaped by a suitable aperture and/or lens.

Hence, light from the emitter module of such a set crosses at least part of the measurement chamber to arrive at the detector module placed within the light cone. Such a pair set be used to measure absorption at the given wavelength while the other detector modules (at least some of which have different center wavelengths) can be used to measure Raman scattering, fluorescence and phosphorescence.

Alternatively or in addition thereto, they may be at least a second set of emitter and detector modules where the detector module is located outside the cone of light of the emitter module. Light measured by detectors of such sets placed outside the light cone can be used to measure scattered light.

For such a second set the detector module is advantageously arranged at an angular location at which the intensity of the emission of the emitter module is less than 10%, in particular less than 1%, of the maximum far-field intensity of the emitter module

Advantageously, the device comprises at least one group of detector modules, in particular several groups of detector modules, wherein this group or each group comprises a plurality of detector modules having different center wavelengths covering the wavelength range of interest. Advantageously, the wavelength range of interest spans at least 100 nm and/or there are at least ten detector modules with different center wavelengths.

The detector modules might be either spaced equidistantly or with a specific pattern around a wavelength or wavelengths of interests. For examples, in the former case, if the range of interest is from 300 to 600 nm and the number of detectors is 30, then different detector modules are spaced by no more than 10 nm. In the latter case, the spacing is non-equidistant and depends on the specific wavelengths of interest. Those wavelengths might be related to Raman features of specific compounds or to other spectral features.

In more general terms, there may be at least 10 detector modules in the group, wherein the center wavelengths of at least some of these detector modules are spaced from the closest other center wavelengths by no more than 10 nm, in particular no more than 5 nm.

Such a group provides spectral coverage for carrying out a Raman spectroscopy measurement with good resolution or other types of spectroscopy such as fluorescence, phosphorescence and absorption

For good resolution, the group comprises a plurality of detector modules having spectral widths of no more than 10 nm in the examples of equidistant detectors outlined above.

Advantageously, the device comprises a plurality of semiconductor dies with each die comprising several of said modules. In other words, the total count of emitter modules and detector modules integrated on the die is larger than one.

Such a die may e.g. integrate the modules of the group mentioned above.

Advantageously, each die comprises at least one emitter module and at least one detector module.

In particular, each die comprises a plurality of detector modules formed by light detectors covered by an optical filter. The light detectors are integrated into the die, and the filter (which is considered, by definition, to form part of the die even if it may be attached in suitable manner to the semiconductor substrate per se) defines the spectral selectivity of the light detectors. The filter may comprise a plurality of filter sections. Each filter section is associated with a light detector. At least some of the filter sections have differing central wavelengths. Thus, several detector modules having different central wavelengths can be formed on a single die, e.g. for forming a group of detector modules described above.

Advantageously, at least some of the detector modules may comprise a multi-pixel photo counter or other types of multi-pixel photon detectors. This is an array of avalanche-photodiodes or other types of photon detectors arranged either in an array with a cumulative analog output, cumulative digital output or per pixel digital output. The photodiodes might be operated in Geiger mode.

In particular, the detector modules might comprise a plurality of detectors based on different light detection technologies.

These type of detectors are highly suitable to measure at low light intensities of Raman spectroscopy or other types of spectroscopy, but it can also be used to measure the larger intensities that occur in the transmission (absorption) measurements thanks to a wide dynamic range of multi-pixel detectors. The number of pixels in a detector module is defined by light intensities of the emitter modules and processes related to light absorption and re-emittance.

The invention also relates to a method for operating the device. Said method comprises at least the following steps: a) Generating a first light pulse at a first wavelength by means of a first subset of the emitter modules. This first light pulse is shorter than 100 ns, in particular shorter than 10 ns when used for Raman, absorption or fluorescence time-resolved measurements or longer than 100 ns in case of steady state measurements. b) During this first light pulse, measuring a first transmission as well as first Raman scattering of the sample at the first wavelength with at least a first subset or the whole set of the detector modules. c) After this first light pulse, measuring first fluorescence and a first phosphorescence for excitation at the first wavelength during a duration of at least 1 ps. The duration of this measurement is advantageously at least 10 ps and/or less than 10 ms.

This procedure may be repeated at several wavelengths, i.e. the method may comprise at least the following further steps: a’) Generating a second light pulse (P2) at a second wavelength by means of a second subset of the emitter modules. This second light pulse (P2) is shorter than 100 ns, in particular shorter than 10 ns. The first and second wavelengths are different. Advantageously, they differ by at least 10 nm, in particular by at least 100 nm. b’) During this second light pulse (P2), measuring a second transmission as well as second Raman scattering of the sample at the second wavelength with at least a second subset of the detector modules. e’) After this second light pulse (P2), measuring second fluorescence and a second phosphorescence for excitation at the second wavelength during a duration of at least 1 ps. The duration of this measurement is advantageously at least 10 ps and/or less than 10 ms.

In this case, the first and second subset of the detector modules may overlap at least partially, in particular completely. In other words, at least some detector modules are used for measuring transmission and/or Raman scattering at both wavelengths. This allows using the same detectors for excitation measurements at different wavelengths.

On the other hand, advantageously, the first and said second subsets of the emitter modules do not overlap, i.e. different emitters are used for the pulses at the different wavelengths, which leads to a spectrally narrower excitation.

For achieving narrowband excitation, each subset of emitter modules advantageously only comprises emitter modules having the same center wavelength.

Advantageously, the method involves generating a plurality of the first light pulses at said first wavelength in a row at a repetition rate of at least 10 MHz, in particular of at least 50 MHz. This allows to carry out Raman spectroscopy over a longer period so as to generate measurements with a better signal-to-noise ratio.

In particular, at least 100 of said first pulses are generated in a row, advantageously at least 1000.

After such a row of first light pulses, the method may comprise the step of switching off the emitter modules for at least 10 ps and measuring the first fluorescence and/or first phosphorescence.

The fluorescence and phosphorescence may be measured by means of a third subset of the detector modules. This third subset is larger than the first subset, taking into account that fluorescence and phosphorescence encompass a wider range of wavelength than the transmission and Raman measurements. In particular, the third subset may encompass all detector modules or is at least larger than the first subset. The first transmission is advantageously measured with a first emitter module and a first detector module arranged within a cone of the light emitter module. In particular, the first emitter module and the first detector module may be arranged on opposing sides of the measurement chamber, but they also might be arranged differently. The Raman scattering is measured with detector modules arranged adjacent to the “first” detector module, i.e. the detector modules in a neighboring region of the first detector module are used for measuring Raman scattering. All other detectors maybe used for measurement of fluorescence and phosphorescence signals either after the initial pulse (time-resolved) or during the longer (steady state) pulses of the excitation wavelength. The longer pulses can be at least 10ms.

In addition to filters, at least some of the light emitter and/or detectors modules may have lenses placed on top of them to crease light collection efficiency. The lenses can be either placed on detector modules only or light emitter modules only or both. Moreover, miniaturized lenses can be placed on individual pixels of group of pixels of multi-pixel detectors.

Brief Description of the Drawings

The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. This description makes reference to the annexed drawings, wherein:

Fig. 1 shows a schematic view of an optical spectroscopy device, Fig. 2 shows an arrangement of emitter modules and detector modules,

Fig. 3 shows an embodiment of the arrangement of the detector modules opposite an emitter module,

Fig. 4 shows a possible design of the spectral ranges of the detector modules of a group,

Fig. 5 shows a die with a plurality of detector modules and an emitter module,

Fig. 6 shows a sectional view along line VI-VI of Fig. 5,

Fig. 7 shows a first pulse trait for carrying out a measurement, Fig. 8 shows a second pulse trait for carrying out a measurement, and

Fig. 9 an alternative design to Fig. 3. Modes for Carrying Out the Invention

Device Design

Fig. 1 shows a possible design of an optical spectroscopy device 2.

The device comprises a measurement head 4, which e.g. includes a tubular section 6, which has an input opening 8a and an output opening 8b. A measurement chamber 10 is formed in tubular section 6 between input opening 8a and output opening 8b.

The fluid to be examined can be conveyed through tubular section 6 between input opening 8a and output opening 8b.

Emitter modules 12a, 12b, 12c (in the following generally referred to by reference number 12) and detector modules 14a, 14b, 14c (in the following generally referred to by reference number 14) are arranged around measurement chamber 10. Advantageously, they are arranged outside tubular section 6, such that tubular section 6 can form a smooth inner wall for measurement chamber 10. Tubular section 6 is transparent to the light used in the measurement described below, at least at the location of the emitter and detector modules 12, 14.

As described in more detail below, there are differing emitter modules 12 that have different center wavelengths. Similarly, there are differing detector modules 14 that have different center wavelengths. In this context, the “center wavelength” of a module is the wavelength of maximum spectral emission or maximum spectral sensitivity of the module.

The device comprises pairs of emitter modules 12 and detector modules 14 that may have equal central wavelength and arranged facing each other across measurement chamber 10 or within a cone of light of a matching emitter module. This may e.g. be the case for emitter module 12c and detector module 14a.

Advantageously, the axis 24 of maximum emission of the emitter module of such a pair may coincide or be offset with the axis 26 of maximum sensitivity of the detector module of the same pair. In this context, “coincides” includes small deviations from the optimum coaxial configuration of the two modules) as long as the transmission efficiency between the emitter module and detector module is at least 50% as compared to the optimum coaxial configuration.

This is illustrated in Fig. 1 for emitter module 12c and detector module 14a, which are assumed to form such a pair having equal central wavelength and facing each other. As can be seen, the axis 24 of maximum emission of emitter module 12c and the axis 26 of maximum sensitivity of detector module 14a coincide in this sense even though they are slightly offset.

In particular and as shown, axis 24 of maximum emission of emitter module 12c and axis 26 of maximum sensitivity of the detector module 14a of the same pair may be parallel but mutually offset by a distance d. This distance d is advantageously no more than a half of the distance D between emitter module 12c and detector module 14a.

The offset d is advantageously parallel to axis 28 of tubular section

6.

Device 2 further comprises a control unit 16. It comprises e.g. a microprocessor or other programmable circuitry that may be programmed and structured to carry out the various methods described here.

Control unit 16 also contains drivers 18 for driving the emitter modules 12, readout electronics 20 for analog or digital procession the signals from the detector modules 14, voltage or current sources 22 for operating the detector modules 14, communication unit 19a for data transmission and power receiver unit 19b for main power of the system.

Module Geometry

Fig. 2 shows an example of the arrangement of the emitter modules 12 and the detector modules 14 arranged around measurement chamber 10.

In the embodiment shown, the emitter modules 12 are arranged in annular, in particular circular, emitter assemblies 30, and the detector modules 14 are arranged in annular, in particular circular, detector assemblies 32, with the emitter assemblies 30 and the detector assemblies 32 being alternatingly and coaxially arranged along axis 28 of measurement chamber 10.

Advantageously, there is a plurality of emitter assemblies 30 as well as a plurality of detector assemblies 32.

Alternatively, there may be mixed annular assemblies, i.e. each annular assembly may comprise both emitter modules 12 and detector modules 14.

One such mixed annular assembly is shown in Fig. 3, as seen along axis 28, where each square represents a unit 34 including at least one emitter module 12 and at least one detector module 14. An embodiment of such a unit is described in more detail below.

As can be seen from Fig. 3, the emitter module 12c with a center wavelength l is arranged opposite across measurement chamber 10 from detector module 14a of the same wavelength l. Thus, the two modules can be used to measure the absorption of the fluid at wavelength l.

Detector module 14a forms part of a group 36 of detector modules that have different center wavelengths.

Each such group 36 has a plurality of detector modules 14 with spaced-apart center wavelengths in order to cover the wavelength range of interest. Advantageously, there are at least 10 such detector modules in the group. This allows recording a spectrum of Raman emission with high resolution.

In the embodiment shown, group 36 comprises several such detector modules 14b — 14g with regularly spaced central wavelengths, with the spacing being D.

However, the spectral spacing of the central wavelengths of the detector modules need not be regular. Fig. 9 shows an example of an embodiment are the central wavelengths are symmetrically but non-regularly spaced around a center wavelength l with offsets +/- Dr +/- D2, etc. Also, non-symmetrical distributions about a center-wavelength can be used.

This is illustrated in Fig. 4, which shows the spectral sensitivity of the detector modules of group 36 along the circumference of measurement chamber 10.

Advantageously, the detector modules 14 of group 36 are arranged such that the offsets of their center wavelengths from the center wavelength of detector module 14a increase with increasing distance from detector module 14a.

In particular, the detector modules 14 of group 36 are arranged along a row with increasing or decreasing center wavelength.

For examples, if the range of interest is from 300 to 600 nm and the number of detectors is 30, then different detector modules are spaced by no more than 10 nm. In the latter case, the spacing is non-equidistant and depends on the specific wavelengths of interest. Those wavelengths might be related to Raman features of specific compounds or to other spectral features.

As shown in Fig. 4, in order to record a continuous spectrum, the detector modules of group 36 advantageously have overlapping spectral ranges.

The detector modules of group 36 advantageously cover a range of at least 50 nm, in particular of at least 100 nm.

The central wavelengths of the detector modules 14 in group 36 may cover a group range ag of at least 50 nm, in particular of at least 100 nm, in order to obtain measurements, in particular for Raman spectroscopy, over a large wavelength range. The spectral spacing D (i.e. the spacing between spectrally closest members) of group 36 may be regular, i.e. have a constant value D over the whole group range ag. However, and as shown in Fig. 4, it may advantageously be smaller close to the center wavelength l of the group than further away from it, thus providing higher spectral resolution close to center wavelength l.

Advantageously, and as shown in Fig. 3, the detector modules 14 of group 36 are arranged in a row and ordered by ascending or descending center wavelengths. This row may e.g. run along an arc of a circle coaxial to axis 28 of measurement chamber 10. Alternatively, it may e.g. run parallel to axis 28 of measurement chamber 10.

At least part of the emitter modules 12 are advantageously arranged in groups 36’ along a row with increasing or decreasing center wavelength. Same as for the detector modules 14, this row may run along an arc of a circle coaxial to axis 28 of measurement chamber 10 or run parallel to axis 28 of measurement chamber 10.

As shown in Fig. 3, the device can comprise a group 36’ of emitter modules 12a, 12b, 12c... and a group 36 of detector modules arranged on opposite sides of measurement chamber 10, facing each other such that spectra at different center wavelength can be recorded between them. Advantageously, these two groups 36, 36’ comprise several pairs of emitter modules 12 and detector modules 14 having equal center wavelengths (with the pairs differing from each other by their center wavelengths) such that several spectra with different center wavelengths can be measured across said groups.

Module Design

The emitter modules 12 and the detector modules 14 may be separate units, e.g. formed by separate, discrete LEDs and photodetectors, e.g. each having a suitable spectral bandpass filter for defining a suitably narrow spectral width and possibly a lens 15a, 15b as shown in dotted lines by way of example and for only two modules, in Figs. 3 and 9.

Costs can be reduced and a higher density can be achieved if the device comprises a plurality of semiconductor dies, with each die comprising several modules 12, 14. For example, each such die may comprise several emitter modules 12 or several detector modules 14 or at least one emitter module 12 and at least one detector module 14.

Figs. 5 and 6 show an example of such a die 37.

Die 37 comprises a plurality of detector modules 14a, 14b, 14c... arranged in a regular, one- or two-dimensional array 38.

The detector modules 14 of die 37 may comprise light detectors 39a, 39b, 39c... (in particular photodiodes), advantageously of identical or different design, integrated into the semiconductor substrate. The light detectors 39a, 39b,

39c... are covered by an optical filter 40. In order to generate detector modules of different spectral properties, filter 40 can comprise a plurality of filter sections 40a, 40b, 40c... associated with the individual light detectors 39a, 39b, 39c... (e.g. by each filter section 40a, 40b, 40c... covering exactly one light detector 39a, 39b, 39c...). The filter sections 40a, 40b, 40c... have differing central wavelengths.

Filter 40 may e.g. be a thin-film interference filter.

The detector modules 14 of die 37 may e.g. form a group 36 as described above.

In the embodiment of Fig. 5 and 6, die 37 comprises at least one emitter module 12. Emitter module 12 may comprise a light emitter 42, which can e.g. be an LED or a laser diode integrated into the semiconductor substrate. If necessary, an optical filter 44 for narrowing the spectral emission of the emitter module may cover the light emitter 42.

The device can comprise a plurality of such dies 37, e.g. arranged in annular assemblies as described above.

Detector Module Technology

As mentioned, the detector modules 14 advantageously comprise photodiodes.

In a particularly advantageous embodiment, they comprise avalanche photodiodes that are able to detect even small amounts of light.

In an even more advantageous embodiment, they comprise multipixel photon counters as defined above, such as devices from the SI 3361 -2050 series of Hamamatsu.

This type of light detector is able to detect very small amounts of light, such that it is well suited for narrow-band detection of Raman emission. It may, however, also be used to detect fluorescence and/or phosphorescence and even be used in transmission measurements, where the light intensities are higher. Advantageously, the gain of the amplifiers 20 is set to be larger when carrying out Raman spectroscopy measurements and fluorescence or phosphorescence with a given detector module 14 than when carrying out and/or transmission measurements where intensity can be much higher.

Alternatively, or in addition thereto, the bias voltage over the avalanche diode and/or multi-pixel photon counters can be varied and be set to a higher value for low-intensity measurements, in particular for Raman spectroscopy measurements and fluorescence or phosphorescence as compared to the measurements of transmission.

Method of Operation

In operation, control unit 16 operates the emitter modules 12 in pulsed manner.

In particular, and as shown in one example in Fig. 7, it generates a first light pulse PI at a first wavelength by means of a first subset of the emitter modules 12.

The “first subset” advantageously only includes emitter modules having the same center wavelength lΐ for narrowband emission.

The length of the first light pulse PI may be shorter than 100 ns, in particular shorter than 10 ns.

During the first light pulse PI, control unit 16 operates detector module(s) 14 having the first center wavelength lΐ, in particular those opposite the pulsed emitter module(s), to measure the transmission/absorption of the fluid under test at first wavelength lΐ (which is called the “first transmission” in the following). Also, it operates the detector modules 14 having center wavelengths close to lΐ, in particular within 100 nm to XI, to measure Raman scattering at first wavelength lΐ (which is called the “first Raman scattering” in the following).

This corresponds to measurement phase Ml in Fig. 7. Measurement phase Ml has substantially the same length of pulse PI, or it may e.g. be slightly longer, e.g. twice as long.

After the first light pulse PI, control unit 16 operates the detector modules 14 to measure fluorescence (measurement phase M2) and phosphorescence (measurement phase M3) for excitation at wavelength lΐ (which are called “first fluorescence” and “first phosphorescence” in the following).

The duration of measurement phase M2 for the fluorescence measurement is advantageously at least 100 ns and/or no more than 100ps. The measurement phase M3 for the phosphorescence begins advantageously after measurement phase M2 and lasts, advantageously, for at least 100 ps and/or for no more than 10 ms.

The detector modules used for measuring the first fluorescence and/or first phosphorescence advantageously include center wavelengths that are at least 100 nm, in particular at least 200 nm, away from first wavelength lΐ .

Overall, fluorescence and phosphorescence are measured during a duration of at least 100 ns, in particular of at least 10 ps and/or during less than 10 ms.

After completion of the phases M2 and M3, a second light pulse P2 is generated. In the embodiment of Fig. 7, second light pulse P2 has a second wavelength XI. (Alternatively, several light pulses of the first wavelength lΐ may be repeated before one of them is followed by the second light pulse P2 of second wavelength XI.)

Again, second light pulse P2 may be shorter than 100 ns, in particular shorter than 10 ns.

Second wavelength XI differs from first wavelength lΐ advantageously by at least 10 nm, in particular by at least 100 nm. By generating light pulses of clearly different wavelengths, more information about the fluid under test can be gained.

Again, during the second light pulse P2, the transmission as well as Raman scattering of the fluid under test is measured, this time with a second subset of the detector modules 14 with center wavelengths XI for the transmission and with center wavelengths close to XI, in particular within 100 nm to XI, to measure Raman scattering at second wavelength XI. (The respective transmission and Raman scattering at second wavelength XI is called the “second transmission” and the “second Raman scattering” in the following.)

After the second light pulse, again fluorescence and phosphorescence (the “second fluorescence” and the “second phosphorescence”) are measured in measurement phases M2 and M3, respectively, in the same manner as for the first light pulse.

It must be noted that, in the scheme of Fig. 7, Raman scattering may include only a small number of photons, much less than fluorescence and/or phosphorescence. Hence, for improved sensitivity, a measurement scheme as shown in Fig. 8 is preferred.

In this scheme, a plurality of first pulses PI at first wavelength lΐ is generated, in particular at least 100 of them, in a row. The repetition rate of the pulses PI is at least 10 MHz, in particular at least 50 MHz. This allows measuring Raman scattering during a larger timespan, i.e. first measurement phase Ml lasts longer and is able to process more photons.

Using a plurality of pulses PI instead of one longer pulse allows to reduce the thermal load of the emitter modules 12 as well as to simplify the electronics for driving the emitter modules 12.

Only then, after the row of first pulses PI ends, the emitter modules are switched off for a longer time, i.e. for at least 10 ps, in particular even for longer, in order to measure the first fluorescence and/or phosphorescence.

Then, the measurement can e.g. be repeated at second wavelength l2 with a plurality of second light pulses P2 in a row.

In general, fluorescence and phosphorescence may be measured by a “third subset” of measurement modules, larger than the “second subset” used for measuring Raman scattering. This is because fluorescence and phosphorescence span a wider spectral range than Raman scattering.

Notes

As mentioned above a detector module of a given center wavelength may be arranged opposite to the emitter module of the same center wavelength, such as e.g. illustrated for the modules 12c and 14a in Fig. 3.

However, even for measuring transmission, the detector module of a given center wavelength may also be arranged off-axis from the emitter module of the same wavelength. For example, in Fig. 3, detector module 14c may have the same center wavelength as emitter module 12c as long as the cone 13 of light of emitter module 12c (indicated by dotted lines in Fig. 3) is wide enough.

The device shown here can be used to examine fluids, e.g. gases and liquids, passing through measurement chamber 6.

The device can in particular be used to measure the properties of blood and other body fluids. It may be used as an implant or external to the body.

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.