METHOD, DEVICE AND SYSTEM FOR DETECTING RAMAN SCATTERED LIGHT

Abstract

A method for detecting Raman scattered light using at least one interference filter and a detection unit, the Raman scattered light to be detected including an incoming scattered light signal, wherein the method includes the following steps: * a first filtered scattered light signal is generated by the application of a first transmission function to the incoming scattered light signal, the first transmission function being assigned to a first optical path length L.sub.1 through a first interference filter, and the first transmission function defining a first spectral band δλ.sub.1; * a second filtered scattered light signal is generated by the application of a second transmission function to the incoming scattered light signal, the second transmission function being assigned to a second optical path length L.sub.2≠L.sub.1 through the first interference filter or through a second interference filter, and second transmission function defining a second spectral band δλ.sub.2; and * the first and the second filtered scattered light signals are detected by the detection unit.

Claims

1. A method for detecting Raman scattered light using at least one interference filter and a detection unit (30), said Raman scattered light to be detected comprising an incoming scattered light signal (10), wherein the method comprises the following steps: generating a first filtered scattered light signal by applying a first transmission function to the incoming scattered light signal, the first transmission function being assigned to a first optical path length L.sub.1 through a first interference filter, the first transmission function defining a first spectral band δλ.sub.1, the first spectral band δλ.sub.1 comprising light with first wavelengths around a first mean wavelength λ.sub.1, the light of the first wavelengths being transmitted through the first interference filter, generating a second filtered scattered light signal by applying a second transmission function to the incoming scattered light signal, the second transmission function being assigned to a second optical path length L.sub.2≠L.sub.1 through the first interference filter or through a second interference filter, the second transmission function defining a second spectral band δλ.sub.2, the second spectral band δλ.sub.2 comprising light with second wavelengths around a second mean wavelength λ.sub.2, the second mean wavelength λ.sub.2 being shifted by a wavelength compared to the first mean wavelength Δλ.sub.2, the light of the second wavelengths being transmitted through the first interference filter or through the second interference filter, and detection of detecting the first and the second filtered scattered light signal with the detection unit.

2. The method according to claim 1, wherein the method further comprises the following steps: generating a reference light signal, generating a first filtered reference light signal by applying the first transmission function to the reference light signal, the filtered reference light signal being assigned to the first filtered scattered light signal, generating a second filtered reference light signal by applying the second transmission function to the reference light signal, the second filtered reference light signal being assigned to the second filtered scattered light signal, detecting the first and second filtered reference light signal with the detection unit, and generating corrected filtered scattered light signals by subtracting the filtered reference light signals from the respectively assigned filtered scattered light signals.

3. The method according to claim 1, wherein a Raman spectrum is generated from the detected scattered light signals or from the corrected scattered light signals.

4. The method according to claim 3, wherein a multivariate data analysis, in particular chemometrics, is used to generate the Raman spectrum.

5. The method according to claim 1, wherein the incoming scattered light signal has a direction of propagation, the method between the generation of the first filtered scattered light signal and the generation of the second filtered scattered light signal comprising a pivoting of the first interference filter relative to the direction of propagation of the incoming scattered light signal, the pivoting of the first interference filter causing a change from the first optical path length L.sub.1 to the second optical path length L.sub.2.

6. The method according to claim 1, wherein the first interference filter is replaced by the second interference filter between the generation of the first filtered scattered light signal and the generation of the second filtered scattered light signal.

7. The method according to claim 1, wherein the incoming scattered light signal propagates divergently or convergently and the generation of the first filtered scattered light signal at a first angle α.sub.1 relative to a reference beam and the generation of the second filtered scattered light signal takes place at a second angle α.sub.2≠α.sub.1 relative to the reference beam and the light of the first wavelengths and the light of the second wavelengths transmitted through the first interference filter.

8. A device for detecting Raman scattered light, wherein the device is designed to carry out the method according to claim 1, wherein the device comprises: a detection unit and a first interference filter or a first and a second interference filter.

9. The device according to claim 8, wherein the device comprises a first lens, the detection unit comprising an array of detector cells, the array being oriented relative to the first lens in such a way that light can be imaged convergently or divergently onto the array by the first lens, wherein the first interference filter is positioned between the first lens and the detection unit.

10. The device according to claim 9, wherein the first lens is designed as a cylindrical lens with a first cylinder axis, the device further comprising a second lens, the second lens being designed as a cylindrical converging lens with a second cylinder axis, the first and the second cylinder axis being oriented perpendicular to one another and the array being positioned along the focal line of the second lens.

11. The device according to claim 10, wherein the second lens is positioned between the first interference filter and the array of detector cells.

12. The device according to claim 8, wherein the first interference filter is pivotably mounted.

13. The device according to claim 12, wherein the detection unit comprises a single detector cell.

14. The device according to claim 8, wherein the first interference filter is designed to be exchangeable by the second interference filter.

15. A system for detecting Raman scattered light, comprising: a light source, in particular a laser source, a device for positioning a sample and an optical device, the optical device being designed to direct the light from the light source onto the sample, wherein the system further comprises the device according to claim 8.

16. The method according to claim 2, wherein a Raman spectrum is generated from the detected scattered light signals or from the corrected scattered light signals, and wherein a multivariate data analysis, in particular chemometrics, is used to generate the Raman spectrum.

17. The method according to claim 16, wherein the incoming scattered light signal has a direction of propagation, the method between the generation of the first filtered scattered light signal and the generation of the second filtered scattered light signal comprising a pivoting of the first interference filter relative to the direction of propagation of the incoming scattered light signal, the pivoting of the first interference filter causing a change from the first optical path length L.sub.1 to the second optical path length L.sub.2.

18. The method according to claim 16, wherein the first interference filter is replaced by the second interference filter between the generation of the first filtered scattered light signal and the generation of the second filtered scattered light signal.

19. The method according to claim 16, wherein the incoming scattered light signal propagates divergently or convergently and the generation of the first filtered scattered light signal at a first angle α.sub.1 relative to a reference beam and the generation of the second filtered scattered light signal takes place at a second angle α.sub.2≠α.sub.1 relative to the reference beam and the light of the first wavelengths and the light of the second wavelengths transmitted through the first interference filter.

20. A system for detecting Raman scattered light, comprising: a light source, in particular a laser source, a device for positioning a sample and an optical device, the optical device being designed to direct the light from the light source onto the sample, wherein the system further comprises the device according to claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0101] In the following, embodiments of the invention are described with reference to figures. The figures show the following:

[0102] FIG. 1 shows a schematic representation of an embodiment with a first converging lens;

[0103] FIG. 2 shows a schematic representation of the embodiment from FIG. 1 from a different perspective;

[0104] FIG. 3 shows a schematic representation of a further embodiment with a pivotable first interference filter;

[0105] FIG. 4 shows a schematic representation of an embodiment with several detectors.

DETAILED DESCRIPTION OF THE INVENTION

[0106] FIG. 1 shows an embodiment of the device 01. The device 01 comprises a first interference filter 20, a detection unit 30, and a first converging lens 22. The detection unit 30 comprises a plurality of detector cells 32 arranged next to one another in a row. Raman scattered light, including an incoming scattered light signal 10, strikes the first converging lens 22. The incoming scattered light signal 10 is composed of the incoming partial beams 11 to 15. The converging lens 22 refracts the incoming scattered light signal 10 and focuses the incoming scattered light signal 10. The focus of the first converging lens 22 lies here within the first interference filter 20.

[0107] The incoming partial beams 11 to 15 strike the surface of the first interference filter 20 at different angles of incidence α. The central incoming partial beam 13 strikes the first interference filter 20 at an angle of incidence α.sub.13=0° (not shown here) and is referred to here as the reference beam. The incoming partial beam 11 hits the first interference filter 20 at the angle of incidence α.sub.11. The incoming partial beam 12 hits the first interference filter 20 at the angle of incidence α.sub.12. The incoming partial beam 14 hits the first interference filter 20 at the angle of incidence α.sub.14. The incoming partial beam 15 hits the first interference filter 20 at the angle of incidence α.sub.15. The angles of incidence α.sub.11, α.sub.12, α.sub.14 and α.sub.15 are not equal to the angle of incidence an and therefore not equal to 0°. In the following, the angles of incidence α.sub.11 to α.sub.15 differ from one another. In other words, the incoming scattered light signal 10 propagates convergently after the converging lens 22.

[0108] The incoming partial beams 11, 12, 13, 14 and 15 run through the first interference filter 20. Since they strike the first interference filter 20 at different angles of incidence α.sub.11 to α.sub.15, the incoming partial beams 11 to 15 pass the first interference filter 20 along different paths with the optical path lengths L.sub.11, L.sub.12, L.sub.13, L.sub.14 and L.sub.15 (not shown here). The different optical path lengths L.sub.11 to L.sub.15 have the effect that a different transmission function is applied to each of the incoming partial beams 11 to 15. If, for example, the first transmission function is applied to the incoming partial beam 13 as a reference, the transmission functions that are applied to the incoming partial beams 11, 12, 14 and 15 are spectrally shifted by the wavelengths Δλ.sub.11, Δλ.sub.12, Δλ.sub.14 and Δλ.sub.15 compared to the first transmission function. By applying the transmission functions to the incoming partial beams 11 to 15, the filtered partial beams 41 to 45 are generated.

[0109] The filtered partial beam 41 is generated from the partial beam 11 at al au relative to the reference beam. The filtered partial beam 42 is generated from the partial beam 12 at the angle α.sub.12≠α.sub.13 relative to the reference beam. The partial beam 43 is generated from the partial beam 13 as a reference beam. The filtered partial beam 44 is generated from the partial beam 14 at the angle α.sub.14≠α.sub.13 relative to the reference beam. The filtered partial beam 45 is generated from the partial beam 15 at the angle α.sub.15≠α.sub.13 relative to the reference beam. The filtered partial beams together form the filtered scattered light signal 40, the filtered partial beam 43 being detected as the first scattered light signal and the remaining, partially superimposed, filtered partial beams 41, 42, 44 and 45 being detected by the detection unit as further scattered light signals.

[0110] The filtered partial beams 41 to 45 strike the detection unit 30, which in this embodiment comprises a plurality of detector cells 32 arranged next to one another. The filtered partial beams 41 to 45 are detected by the detector cells 32. Using chemometric methods, a Raman spectrum of the measured sample can be created from the filtered scattered light signal 40, in particular from the filtered partial beams 41 to 45, after the detection.

[0111] In the embodiment shown here, an optional second converging lens is positioned between the first interference filter 20 and the detection unit 30. The converging lens is a cylindrical converging lens whose focal line lies on the detection unit 30 and which focuses the filtered partial beams 41-45 in a plane perpendicular to the image plane onto the detector cells 32 of the detection unit 30.

[0112] A view of the embodiment from FIG. 1 rotated by 90° is shown in FIG. 2. The partial beams 11-15 run through the first converging lens 22 and the first interference filter 20 without being refracted in the image plane shown. The second converging lens 24 focuses the filtered partial beams 41-45 onto the detector cells 32 of the detector unit 30. The individual detector cells 32 are arranged one behind the other in this view.

[0113] FIG. 3 shows a further schematic illustration of an embodiment of the device 01. The device 01 comprises a detection unit 30 which is formed from a single detector cell 32. The device 01 further comprises a first interference filter 20. The first interference filter 20 is designed to be pivotable, the first interference filter 20 being pivotably mounted in the pivoting direction R. The position of the pivot axis and thus the specific design of the filter holder and the pivot mechanism are not important here. A first interference filter 20 pivoted by the angle α is shown with a dashed line.

[0114] If the incoming scattered light signal 10 hits the surface of the first interference filter 20, the wavelength 61 of a spectral shift in the transmission function of the first interference filter 20 depends on the angle of incidence α between the direction of propagation of the incoming scattered light signal 10 and the perpendicular to the surface of the first interference filter 20. If the first interference filter 20 is pivoted about the pivot axis (here lying within the first interference filter 20) in the pivoting direction R, the angle of incidence α of the incoming scattered light signal on the first interference filter 20 changes. If the first interference filter is pivoted within the illustrated image plane, as indicated here by the dashed line, then the angle ε, by which the first interference filter is pivoted, is equal to the change in the angle of incidence α. This structure enables the use of different transmission functions, which are spectrally shifted relative to one another by the wavelength Δλ as a function of the angle ε.

[0115] The first interference filter 20 generates a filtered scattered light signal 40 from the incoming scattered light signal 10 by applying the transmission function which is dependent on the angle ε. The filtered scattered light signal 40 is detected by the detector cell 32 of the detection unit 30. In order to apply different transmission functions to the incoming scattered light signal 10, several measurements are carried out in this embodiment, each with different positions of the first interference filter 20, so that with each measurement the incoming scattered light signal 10 hits the first interference filter 20 at a different angle of incidence α.

[0116] FIG. 4 shows a schematic representation of a further embodiment of the device 01 and how it is used for the detection of Raman scattered light. The device 01 is placed in the beam path of a laser beam 54, the laser beam 54 being generated by a laser source 52.

[0117] In the center of the device 01, a capillary 56 runs perpendicular to the image plane. A mixture, which comprises a sample to be examined, flows through the capillary 56 either into the image plane or out of the image plane. The wall of the capillary 56 that is transparent to the laser light is shown hatched in FIG. 4.

[0118] The laser beam 54 traverses the device 01, penetrating the capillary 56. The laser light of the laser beam 54 is at least partially scattered on the sample within the capillary 56 in all directions, as a result of which the not yet detected scattered light propagates as a scattered light signal 10 (to be detected and received) in all directions. A transmission detector 58, which detects and/or absorbs the non-scattered laser light, is positioned behind the device 01. The directions of propagation of the incoming scattered light signals 10 and of the laser beam 54 are indicated here by arrows.

[0119] The device further comprises a plurality of detectors 60 which are arranged in a circle around the capillary 56. The arrangement of the detectors 60 is interrupted in the areas of the beam path of the laser beam 54, so that the laser beam 54 is not blocked by the detectors 60 or the detectors 60 detect the unscattered laser light.

[0120] The detectors 60 each comprise at least one detection unit and at least one interference filter. The detectors 60 can optionally comprise one or more converging lenses. The detection units can furthermore each comprise one or more detection cells.

[0121] The detectors 60 differ from one another in that the interference filters filter different spectral ranges. The interference filters in the detectors 60 can, for example, be oriented differently to the respective direction of propagation of the incoming scattered signals 10, so that the incoming scattered light signals 10 hit the interference filters at different angles α. Alternatively or additionally, the interference filters can be coated with different thicknesses. In other words, the detectors 60 differ from one another by different optical path lengths L due to their interference filters.

[0122] The incoming scattered light signals 10 are detected as filtered scattered light signals by the detection units of the detectors 60 after they have been transmitted through the interference filters. Finally, a Raman spectrum can be generated from the detected scattered light signals.

[0123] With the embodiment of the device according to FIG. 4, several measurements can advantageously be carried out in parallel.

LIST OF REFERENCE SYMBOLS

[0124] 01 device [0125] 10 incoming scattered light signal [0126] 11 incoming partial beam [0127] 12 incoming partial beam [0128] 13 incoming partial beam [0129] 14 incoming partial beam [0130] 15 incoming partial beam [0131] 20 first interference filter [0132] 22 first converging lens [0133] 24 second converging lens [0134] 30 detection unit [0135] 32 detector cell [0136] 40 filtered scattered light signal [0137] 41 filtered partial beam [0138] 42 filtered partial beam [0139] 43 filtered partial beam [0140] 44 filtered partial beam [0141] 45 filtered partial beam [0142] 52 laser source [0143] 54 laser beam [0144] 56 capillary [0145] 58 transmission detector [0146] 60 detector [0147] R swivel direction [0148] Δλ.sub.1,2,i wavelength of the spectral shift [0149] λ.sub.1,2,i mean wavelength [0150] L.sub.1,2,i optical path length [0151] δλ.sub.1,2,i spectral band [0152] α angle of incidence [0153] ε angle