Equipment for performing polarization-resolved Raman spectroscopy

Abstract

A device for performing polarization-resolved Raman spectroscopy on a sample (15), in particular a crystalline sample, the device comprising: at least one light source (11), in particular at least one laser, for providing excitation radiation to the sample (15); a spectrometer (31) for separating light from the sample (15), in particular Raman scattered light from the sample (15), into at least one spectrum of spatially separated wavelength components, and for directing at least a portion of the at least one spectrum to a detector (29), in particular a CCD detector; a polarization state control element (27) for the light from the sample (15), the polarization state control element (27) being arranged in the light path of at least one light beam (25) travelling from the sample (15) towards the detector (29), and the polarization state control element (27) comprising at least one polarization-sensitive optical element (45, 47), in particular a Wollaston prism, the at least one polarization-sensitive optical element being suitable for separating the at least one light beam (25) into at least two, in particular orthogonal polarized light beams (35a, 35b, 37a, 37b).

Description

[0001] The present invention relates to an apparatus for performing polarization-resolved Raman spectroscopy on a sample, in particular a crystalline sample.

[0002] Spectroscopy generally refers to the process of measuring the energy or intensity as a function of the wavelength in a beam of light. Spectroscopy uses the absorption, emission or scattering of light by physical matter (especially atoms, molecules or ions) to qualitatively and quantitatively study the physical properties and processes of matter.

[0003] The light or radiation directed to the sample during operation of the spectrometer system can be referred to as incident radiation. The redirection of the incident radiation after contact with the sample is generally referred to as scattering of the radiation. To the extent that atoms or molecules in the sample absorb all or part of the incident radiation instead of reflecting it, the sample can become excited and the energy level of the sample can increase to a higher energy level. The light can be scattered, but can continue to have the same wavelength as the incident radiation, a condition generally referred to as Rayleigh scattered light or elastically scattered light. The incident radiation scattered by the sample during, for example, a change in the vibrational state of the molecule can be scattered with different energies, and this scattered light can be referred to as Raman scattered light. This phenomenon has been used in conjunction with spectroscopic analysis to qualitatively and quantitatively study physical properties and processes, including identifying the chemical properties, composition, and structure of the sample.

[0004] If the incident radiation is directed to the sample, the wavelength of the incident radiation can remain substantially unchanged in the scattered radiation. Alternatively, if the incident radiation is directed to the sample, the wavelength in the scattered radiation can acquire one or more wavelengths different from the incident wavelength. The energy difference between the incident radiation and the scattered radiation can be referred to as the Raman shift. Spectroscopic measurement of Raman scattered light can seek to measure the final wavelength of this scattered light.

[0005] The phenomenon of Raman scattered light is useful in spectroscopic analysis applications for studying the quality and quantity of physical properties and processes, including identifying the chemical nature, composition and structure in a sample. Raman shift spectroscopy is used for qualitative and quantitative studies of samples. If incident radiation is used to scatter light from a sample, and the scattered radiation data is measured, the scattered radiation can provide one or more frequencies associated with the sample, as well as the intensity of those shifted frequencies. The frequencies can be used to identify the chemical composition of the sample.

[0006] A Raman spectrometer is an example of a spectrometer for measuring inelastic scattered light, and it is often used to obtain a Raman spectrum of a sample. When a sample is illuminated with monochromatic light, for example from a laser, the light scattered by the sample will contain wavelength components that are different from those present in the incident light. So-called Raman scattering of light on molecules present in the sample often produces this effect. In a Raman spectrometer, the light scattered by the sample is collected, and the spectral distribution of wavelength components with wavelengths different from that of the light source is detected, for example in the form of a visible Raman spectrum.

[0007] In some measurements of Raman spectroscopy, it may be necessary to obtain information about the polarization of the Raman scattered light. For example, the polarization-dependent properties of Raman scattering depend on the single-crystalline quality and crystal orientation of the substrate, which consists of, for example, a single-crystalline silicon (Si) wafer.

[0008] Ramabadran et al. describe in the scientific publication: "Intensity analysis of polarized Raman spectra of off-axis single-crystalline silicon", Material Science & Engineering B 230, pages 31-42, 2018, that polarized backscattered Raman spectroscopy can be used to identify the crystal orientation of the silicon cut-off axis.

[0009] Munisso et al. proposed in the scientific publication "Raman tensor analysis of sapphire single crystals and its application to define the crystal orientation in polycrystalline alumina", Phys. Status Solidi B 246, No. 8, pp. 1893-1900 (2009), a tensor algorithm for practical determination of unknown crystal textures in polycrystalline alumina materials.

[0010] It is an object of the present invention to provide an efficient way for performing polarization resolved spectroscopic analysis on a sample.

[0011] This object is met by a device according to the features of claim 1. Preferred embodiments of the invention are described in the dependent claims.

[0012] According to the present invention, a device for performing polarization-resolved Raman spectroscopy on a sample (especially a crystal sample) comprises:

[0013] at least one light source, in particular at least one laser, for providing excitation radiation to the sample,

[0014] a spectrometer for splitting light from the sample, in particular Raman scattered light from the sample, into at least one spectrum of spatially separated wavelength components, and for directing at least a part of the at least one spectrum to a detector, in particular a CCD detector,

[0015] A polarization state control element for light coming from a sample, the polarization state control element being arranged in the light path of at least one light beam travelling from the sample towards a detector and comprising at least one polarization-sensitive optical element, in particular a Wollaston prism, suitable for splitting the at least one light beam into at least two, in particular orthogonally polarized light beams.

[0016] Each detected spectrum is obtained from a polarized light beam with a known polarization. This is due to the use of the at least one polarization-sensitive optical element, which splits the incident light beam into at least two polarized light beams that leave the at least one polarization-sensitive optical element and travel toward the detector. The registration of the detector to the spectrum occurs simultaneously.

[0017] Spectra detected at different polarizations can be used for crystal analysis of crystalline samples (e.g. silicon), for example if an algorithm based on the Raman tensor scattering theory of silicon is applied to measure the spectra. For example, an algorithm is described in the previously mentioned scientific publication by Ramabadran et al.: "Intensity Analysis of Polarized Raman Spectra of Off-Axis Single Crystal Silicon", Material Science & Engineering B 230, pp. 31-42, 2018. The information obtained from the spectra in combination with the algorithm can be used, for example, to identify crystal planes and face rotation angles in randomly grown silicon polycrystals. The information obtained can further be used to reconstruct the crystallographic map using, for example, the same principles as established in two-dimensional X-ray crystallography, as described, for example, by B. Larson, W. Yang, G. Ice, J. Budai, J. Tischler in the scientific article: "Three-dimensional X-ray structure microscopy with submicron resolution" (Nature, Vol. 415, pp. 887-890, 2002).

[0018] Raman scattering on a sample can be due in particular to the vibrational bonds of the sample. Such vibrational bonds can be pumped most efficiently when the incident light has the same polarization / orientation as the vibrational bonds. If the orientation of the vibrational bonds is orthogonal to the polarization direction of the incident light, they will be excited with low efficiency. Therefore, analysis of the Raman spectrum obtained from the sample can be used to determine, for example, the orientation of atomic or molecular bonds in a crystal or crystal unit cell. This also applies to samples with a polycrystalline structure, such as polycrystalline sapphire or silicon, or inorganic or organic crystals with more complex unit cells, such as crystalline drugs, amino acids, peptides or proteins, as well as to other samples, such as semiconductors, inorganic composites (such as ceramics, piezoelectric materials and ferroelectric materials, and superconductors, etc.), drugs and biomolecules.

[0019] Crystallographic analysis of samples using Raman scattering is also more cost-effective than X-ray diffraction, electron diffraction, and neutron diffraction. For example, X-ray diffraction requires expensive equipment and may even require the use of synchrotron radiation, which is only available in specialized laboratories.

[0020] The device can be used in raster scanning mode. In particular, the device can be used to measure a surface point of a sample. After this, the sample or the focus on the surface is moved to measure at another surface point. In this way, the surface can be scanned and measurement results can be obtained from a plurality of surface points. Thus, 2D or 3D mapping can be performed, which can enable the generation of a 2D or 3D image of a crystal plane of the sample.

[0021] Preferably, the apparatus does not contain any movable parts, such as means for rotating the sample, so that it can be implemented in an easy to use setup. However, it is possible to move the sample relative to the focus of the beam illuminating the sample, in particular to enable scanning of the surface of the sample.

[0022] The at least one polarization-sensitive optical element may in particular be at least one Wollaston prism, which can separate randomly polarized or non-polarized light into two separate linearly polarized outgoing light beams. The Wollaston prism may consist of two calcite prisms, which are bonded together on their substrates to form two right-angled triangular prisms with perpendicular optical axes. Wollaston prisms are commercially available from various suppliers.

[0023] The polarization state control element may include: at least one beam splitting element, which is suitable for splitting the light beam into at least two separate beams, in particular at least two parallel beams; and at least two polarization-sensitive optical elements, in particular two Wollaston prisms, which are arranged so that one of the two separate beams passes through one polarization-sensitive optical element and the other of the two separate beams passes through the other polarization-sensitive optical element.

[0024] Therefore, the light beam from the sample can be divided into at least two separate light beams by using a beam splitting element, which can be a beam splitter. Each separate light beam passes through a polarization-sensitive optical element, such as a Wollaston prism, where each separate light beam is further divided into two, in particular orthogonal polarized light beams. The spectrum of each of the at least four polarized light beams can be detected simultaneously on different areas of the detector. Therefore, the device provides at least 4 detection channels, each channel allowing the detection of a polarization-resolved spectrum of light scattered from the sample. If the polarized light on the sample irradiates more than one light spot, the number of detected spectra can be increased because each light spot can provide a spectrum for each detection channel. Therefore, two irradiated light spots can produce 8 spectra that can be detected.

[0025] Preferably, a wave plate, in particular a half-wave plate or a quarter-wave plate, can be arranged in at least one optical path between the beam splitting element and one polarization-sensitive optical element.Wave plates are known and commercially available.

[0026] A wave plate arranged in the optical path before a polarization-sensitive optical element helps to adjust the polarization of the separated light beams traveling through this wave plate. Thus, Raman spectra with different polarizations can be detected in different detection channels.

[0027] The polarization state control element may include at least one beam splitting element and three polarization-sensitive optical elements, the at least one beam splitting element being suitable for splitting the light beam into three separate beams, in particular at least three parallel beams, the three polarization-sensitive optical elements being arranged such that a first separate beam of the three separate beams passes through a first polarization-sensitive optical element among the polarization-sensitive optical elements, a second separate beam of the three separate beams passes through a second polarization-sensitive optical element among the three polarization-sensitive optical elements, and a third separate beam of the three separate beams passes through a third polarization-sensitive optical element among the three polarization-sensitive optical elements.

[0028] The beam splitting element can equally split the incident beam into three separate beams, so that they can have the same intensity.

[0029] Each of the three split beams passes through one of the polarization-sensitive optical elements, wherein each split beam is further split into two, in particular orthogonal, polarized beams. As a result, a total of six polarized beams can pass through the spectrometer, residing in six spectra that can be detected by using a detector. Thus, the device provides six detectable channels, through which it is possible to simultaneously detect Raman spectra.

[0030] Preferably, a wave plate, in particular a half-wave plate or a quarter-wave plate, is arranged in at least one optical path between the beam splitter and one of the three polarization-sensitive optical elements.

[0031] A first wave plate, in particular a half-wave plate, can be arranged in the optical path between the beam splitting element and the first polarization-sensitive optical element.

[0032] Preferably, a second wave plate, in particular a quarter wave plate, is arranged in the optical path between the beam splitting element and the second polarization-sensitive optical element.

[0033] Preferably, no wave plate is arranged in the optical path between the beam splitting element and the third polarization-sensitive optical element.

[0034] Thus, two of the three separated beams pass through wave plates, in particular, one beam can pass through a half-wave plate and one beam can pass through a quarter-wave plate. Thus, the six spectra that can be detected can include information that can be interpreted as a rotation of the analyzer by 0° and 90° in the scattered Raman signal, corresponding to the linear laser polarization plane, for depolarization studies of the vibrational peaks, at +45° and -45° for polarization rotation measurements, and portions of left and right circularly polarized light can be detected on both channels. The polarization angles in all six channels can be different and can be optimized for a specific application. After the spectral acquisition, as described before, the matrix deflection theory can be applied to the measured spectra and information about the total depolarization of the vibrational peaks, artifacts and orientation distribution parameters can be recovered.

[0035] The polarization state control element can be arranged in the light path between the sample and the spectrometer. The polarization state control element can in particular be arranged between the sample and the entrance slit of the spectrometer. Thus, the separated polarized light beams enter the spectrometer and the polarization resolved spectra (each spectrum is associated with one of the separated polarized light beams) can be detected by the detector, in particular in a specific area of ​​the detector.

[0036] At least one beam splitting element may be arranged in the light path between the light source and the sample, the beam splitting element being adapted to split the light beam from the light source into at least a first light beam and a second light beam. Thus, at least a first light beam and a second light beam obtained by splitting an original light beam originating from the light source may be incident on the sample. The two light beams may be combined at slightly different angles between their propagation axes. This may result in two light spots locally separated from each other in a focal plane on or in the sample. Thus, the spectral responses from the light spots obtained on the detector may be spatially separated from each other and may be detected in different areas of the detector.

[0037] A wave plate (preferably a half-wave plate or a quarter-wave plate) can be arranged in the optical path of the second light beam between the beam splitting element and the sample for generating a polarization-controlled second light beam. The polarization of the second light beam can thus be adjusted.

[0038] Preferably, at least one beam combiner can combine the first beam and the polarization-controlled second beam and direct the combined beam onto the sample, preferably producing two spatially separated light spots in the same focal plane on the sample. This can also have the effect that the spectral responses detected by the detector are spatially separated from each other. This means that different spectra can be detected in different areas of the detection window of the imaging sensor.

[0039] The at least one beam splitting element may be adapted to split the light beam from the light source into a first light beam, a second light beam and a third light beam.Thus, the three light beams may be incident on the sample and focused on spatially separated light spots on or in the sample.

[0040] Preferably, a wave plate (eg a half-wave plate or a quarter-wave plate) may be arranged in the optical path of the second light beam between the beam splitting element and the sample for generating a polarization-controlled second light beam.

[0041] Another wave plate (preferably a half wave plate or a quarter wave plate) can be arranged in the optical path of the third beam between the beam splitting element and the sample for generating a polarization-controlled third beam. The polarization of the corresponding beam can thus be adjusted.

[0042] At least one beam combiner may be configured to combine the first beam, the polarization-controlled second beam, and the polarization-controlled third beam, and direct the combined beam onto the sample.

[0043] The at least one beam combiner and / or the beam paths before and after the beam combiner are preferably arranged such that the combined beam is directed to three spatially separated light spots generated in the same focal plane on or in the sample.

[0044] At least one beam combiner may be arranged to combine two or more light beams from two or more different light sources and direct the combined light beam onto the sample, preferably to spatially separated light spots in the same focal plane on the sample. Thus, the light beam incident on the sample and used to generate Raman scattered light from the sample may be provided by two or more light sources. The light sources may provide light of different wavelengths, for example one light source may provide a 780 nm laser, one light source may provide a 785 nm laser, and another light source may provide a 790 nm laser.

[0045] The light beam from at least one of the light sources may be a polarization controlled light beam. This may be achieved, for example, by using a polarizer placed in the light path of the light beam emerging from the light source. The polarization of at least one of the light beams incident on the sample may thus be adjusted.

[0046] The invention also relates to a system for determining at least one property of a crystalline sample, in particular the orientation of a surface plane of the crystalline sample, the system comprising:

[0047] The device according to the invention, and

[0048] A computer system adapted to employ spectra obtained by the apparatus from measurements of the sample with an algorithm based on Raman tensor scattering theory, the algorithm being executable by the computer system to obtain crystal information about the sample.

[0049] The invention also relates to a method for performing at least one measurement on a crystalline sample, the method comprising the step of simultaneously obtaining at least two spectra from the sample using a device according to the invention.

[0050] Preferably, the method further comprises the step of using the spectrum in a pre-set algorithm, in particular implemented on a computer system, to obtain crystal information about the sample.

[0051] One or more examples will be described below in conjunction with the following drawings, wherein like reference numerals represent like elements, and

[0052] Figure 1 schematically shows a first variant of a device for performing polarization-resolved Raman spectroscopy on a sample,

[0053] Figure 2 schematically shows a second variant of a device for performing polarization-resolved Raman spectroscopy on a sample,

[0054] Figure 3 schematically shows a third variant of a device for performing polarization-resolved Raman spectroscopy on a sample, and

[0055] Figure 4 A fourth variant of a device for performing polarization-resolved Raman spectroscopy on a sample is schematically shown.

[0056] Figure 1 The device shown comprises at least one light source 11, which is preferably a laser, for providing a beam 13 of excitation radiation to a sample 15, in particular, the beam 13 (which is in particular a laser beam) is split into two orthogonally polarized laser beams. Therefore, preferably, the two orthogonally polarized laser beams 13 are incident on the sample 15. The two orthogonally polarized laser beams 13 are reflected by a dichroic mirror 17 and further guided by mirrors 19 and 21 to an objective lens 23 comprising a plurality of lenses to focus the laser beam 13 on the sample 15.

[0057] The orthogonal laser beam 13 is slightly deviated in its propagation direction, so that the objective lens focuses it into two spatially separated light spots 303 , 305 , as shown in the window 301 obtained from a photograph of the focal plane on the sample 15 .

[0058] The optical arrangement is arranged in a backscattering geometry, so that the objective lens 23 is also used to collect light scattered from the sample 15, in particular light scattered from the two illuminated light spots 303, 305. The backscattered light beam 25 (at least the spectral component of the backscattered light beam that is different from the spectral component of the laser beam 13) can pass through the dichroic mirror 17 and enter the polarization state control element 27 for the light beam 25 scattered from the sample 15.

[0059] The polarization state control element 27 is arranged in the optical path of the light beam 25 collected by the objective lens 23 and the light beam travels towards the detector 29 before passing through the spectrometer 31 in the optical path. The polarization state control element 27 includes a beam splitter 33, which is suitable for splitting the light beam 25 into a first separated light beam 35 and a second separated light beam 37, which travel parallel to each other after the first separated light beam 35 is reflected by the reflector 39.

[0060] The first light beam 35 passes through a half-wave plate 41 , while the second light beam 37 passes through an optical element 43 , such as a quarter-wave plate, which may also change the polarization state of the second light beam 37 .

[0061] Subsequently, the first light beam 35 passes through a first polarization-sensitive optical element, here a first Wollaston prism 45, which splits the first light beam 35 into two orthogonal polarized light beams 35a, 35b. Figure 1 The polarization of the beam 35a may be, for example, 0°, and the polarization of the beam 35b may be, for example, 90°. The second beam 37 passes through a second polarization-sensitive optical element, here a second Wollaston prism 47, which splits the second beam 37 into two orthogonal polarized beams 37a, 37b, which are polarized at Figure 1 The polarization of beam 37a may be, for example, +45°, and the polarization of beam 37b may be, for example, -45°.

[0062] Figure 1 The optical system of the device further comprises a lens system 49 which may also be a slit lens and which is adapted to focus the polarized light beams 35a, 35b, 37a, 37b leaving the Wollaston prisms 45, 47 through the slit 51 of the spectrometer 31. The lens system 49 may also comprise an edge filter.

[0063] The spectrometer 31 comprises a collimating lens system 53 with a focus in the slit. The collimating lens system 53 transforms the light beams 35a, 35b, 37a, 37b into a collimated light beam which can pass through an optional edge filter (not shown) and a transmission grating 55.

[0064] The grating 55 splits each of the light beams 35a, 35b, 37a, 37b into corresponding spectra of spatially separated wavelength components, and directs at least a portion of each spectrum onto the pixel array 59 of the detector 29 via the focusing lens system 57 to detect the spectrum of each polarized light beam 35a, 35b, 37a, 37b.

[0065] Window 307 shows the spectrum measured on pixel array 59. As can be seen, eight different spectra can be measured simultaneously. The spectra are separated from each other along the y-axis. The light spots spatially distributed along the x-axis are associated with different wavelengths contained in each spectrum.

[0066] The eight spectra are due to the sample 15 being irradiated into two light spots by two beams of different polarizations. Therefore, the backscattered beam 25 actually includes two backscattered Raman beams due to the different polarizations of the two light spots 303, 305 and the incident light. Therefore, the sample response from different incident laser polarizations is collected at the same time. In addition, the beam splitter 33 separates each of the two backscattered Raman beams so that it passes through each Wollaston prism 45, 47. Therefore, each of the polarized beams 35a, 35b, 37a, 37b actually includes two beams, which is due to the two light spots irradiated with different laser polarizations. Therefore, a total of eight beams leave the Wollaston prism and pass through the entrance slit 51 of the spectrometer 31. This is shown in window 309, which is obtained from a photograph of the plane of the slit 51, and shows eight beams traveling through the slit 51, wherein they are separated from each other in space. This explains the eight spectra detectable on the pixel array 59.

[0067] Figure 2 The optical setup of the device essentially corresponds to Figure 1 The optical setup of the device. Figure 2 The device can also detect eight spectra simultaneously as described above.

[0068] Figure 2 The device comprises a laser 11 as a light source, which emits light of 785nm wavelength. The laser 11 can be a diode laser, for example. A beam splitter 63 splits the laser beam 61 into two beams 65, 67. The beam 65 passes through a half-wave plate 69, which changes the polarization of the beam 65. The beam 71 and the beam 67 emitted from the half-wave plate 69 are combined into a laser beam 13 by a reflector 73 and a beam splitter 75.

[0069] As reference Figure 1 As explained above, beam 13 is therefore actually composed of two beams with different polarizations. Beams 67 and 71 will combine so that their propagation axes are slightly offset from each other. This will produce two light spots in the sample focal plane (similar to Figure 1 For example, the propagation axis of the light beam 67 may be adjusted by tilting the reflector 73.

[0070] Figure 3 The optical setup of the device is similar to that described previously Figure 1 and Figure 2The optical setup of the device is shown in Figure 1. However, the light emitted by the laser 11 passes through some optical elements 77, 79, 81, 83 with a linear filter 79 and linear polarizers 81, 83, is reflected by a mirror 85 and is separated into three beams 89, 91, 93 by using a beam splitter 87. The separated beam 89 passes through a wave plate 95 and the separated beam 91 passes through a wave plate 97, while the beam 93 does not pass through the wave plate. This results in three beams with 0°, 45° and 90° polarization, which are combined at slightly different angles on their propagation axes by using beam splitters 99 and 101, resulting in three light spots 313, 315 and 317 as shown in the window 311 in the focal plane on the sample 15.

[0071] The path of the backscattered light corresponds essentially to the above description of Figure 1 As a result, due to the three light spots 313, 315, 317 caused by the light of different polarizations and the separation of the light beams from these light spots in the polarization state control element 27, 12 polarization-resolved light beams pass through the slit 51 which may be equipped with a shutter, as shown in the window 312. Therefore, as shown in the window 319, 12 polarization-resolved Raman spectra can be detected on the pixel array of the detector 29.

[0072] As an option, Figure 3 The optical arrangement of the device may include a polarization state control element 27, which includes at least one beam splitting element, which is suitable for splitting the light beam from the sample into three separate beams. A first wave plate (e.g. a half-wave plate) may be arranged in the light path between the beam splitting element and the first polarization-sensitive optical element (in particular the first Wollaston prism). A second wave plate (in particular a quarter-wave plate) may be arranged in the light path between the beam splitting element and the second polarization-sensitive optical element (in particular the second Wollaston prism). No wave plate may be arranged in the light path between the beam splitting element and the third polarization-sensitive optical element (in particular the third Wollaston prism (not shown)). As previously described, each Wollaston prism splits each incident light beam into two separate linear outgoing light beams.

[0073] Thus, for each incident beam, the three Wollaston prisms produce six outgoing beams that travel toward the spectrometer 31. Thus, three beams originating from Raman scattering in the light spots 313, 315 can produce 18 beams that leave the three Wollaston prisms. Thus, as shown in window 319, 18 spectra can be detected on the pixel array of the detector 29.

[0074] Figure 4 The optical setup of the device essentially corresponds to Figure 3 The optical setup of the device. However, Figure 4The device comprises three lasers 11a, 11b and 11c, irradiating linearly polarized light of 780nm, 785nm and 790nm. The polarization of the light from laser 11c is changed by 45° by wave plate 95, and the polarization of the light from laser 11b is changed by 90° by wave plate 97. The light from the three lasers is combined by using a mirror 85 and beam splitters 99, 101, so that the laser beams propagate slightly in different directions, again producing three laser light spots with different polarizations (0°, 45°, 90°) as shown in window 323 (obtained from the image of the focal plane of objective lens 23). Due to the different lasers 11a, 11b, 11c, these light spots are irradiated by light of different wavelengths.

[0075] The information obtained from the measured spectrum can be used for example in the algorithm described in the article by Ramabadran et al. mentioned above. The algorithm can be based on the Raman tensor scattering theory. Thus, for example, by using the same principles as in X-ray crystallography, a crystal map of the sample can be obtained.

[0076] List of reference numerals

[0077] 11 Light source, laser

[0078] 11a Laser

[0079] 11b Laser

[0080] 11c Laser

[0081] 13 Laser Beam

[0082] 15 samples

[0083] 17 Dichroic Mirror

[0084] 19 Reflector

[0085] 21 Reflector

[0086] 23 Objective lens

[0087] 25 Beam

[0088] 27 Polarization state control element

[0089] 29 Detector

[0090] 31 Spectrometer

[0091] 33 Beam splitter

[0092] 35 First split beam

[0093] 35a Polarized beam

[0094] 35b Polarized beam

[0095] 37 Second split beam

[0096] 37a Polarized beam

[0097] 37b Polarized beam

[0098] 39 Reflector

[0099] 41 Half-wave plate

[0100] 43 Optical Components

[0101] 45 First Wollaston Prism

[0102] 47 Second Wollaston Prism

[0103] 49 Lens System

[0104] 51 Slit

[0105] 53 Collimating lens system

[0106] 55 Grating

[0107] 57 Focusing lens system

[0108] 59-pixel array

[0109] 61 Laser

[0110] 63 Beam Splitter

[0111] 65 Beam

[0112] 67 Beam

[0113] 69 Half-wave plate

[0114] 71 Beam

[0115] 73 Reflector

[0116] 75 Beam Splitter

[0117] 77 Optical Components

[0118] 79 Optical elements, linear filters

[0119] 81 Optical elements, polarizers

[0120] 83 Optical elements, polarizers

[0121] 85 Reflector

[0122] 87 Beam Splitter

[0123] 89 Beam

[0124] 91 Beam

[0125] 93 Beam

[0126] 95 Wave Plate

[0127] 97 Wave Plate

[0128] 99 Beam Splitter

[0129] 101 Beam Splitter

[0130] 301 Window

[0131] 303 Light Point

[0132] 305 Light Point

[0133] 307 Window

[0134] 309 Window

[0135] 311 Window

[0136] 313 Light Point

[0137] 315 Light Point

[0138] 317 Light Spot

[0139] 319 Window

[0140] 321 Window

[0141] 323 Window

Claims

1. A device for performing polarization-resolved Raman spectroscopy on a sample (15), the device comprising: at least one light source (11) for providing excitation radiation to the sample (15), a spectrometer (31) for splitting light from the sample (15) into at least one spectrum of spatially separated wavelength components and for directing at least a portion of the at least one spectrum to a detector (29), a polarization state control element (27) for light coming from a sample (15), said polarization state control element (27) being arranged in the light path of at least one light beam (25) travelling from said sample (15) towards said detector (29), and The polarization state control element (27) comprises at least one polarization-sensitive optical element, the at least one polarization-sensitive optical element being adapted to split the at least one light beam (25) into at least two polarized light beams, The polarization state control element (27) includes at least one beam splitting element and three polarization-sensitive optical elements, wherein the at least one beam splitting element is suitable for splitting the light beam into three separate beams, and the three polarization-sensitive optical elements are arranged so that a first separate beam of the three separate beams passes through a first polarization-sensitive optical element of the polarization-sensitive optical elements, a second separate beam of the three separate beams passes through a second polarization-sensitive optical element of the three polarization-sensitive optical elements, and a third separate beam of the three separate beams passes through a third polarization-sensitive optical element of the three polarization-sensitive optical elements.

2. The device according to claim 1, wherein: The sample is a crystalline sample.

3. The device according to claim 1, wherein: The at least one polarization-sensitive optical element is a Wollaston prism.

4. The device according to claim 1, characterized in that The polarization state control element (27) comprises at least one beam splitting element (33) and at least two polarization-sensitive optical elements, wherein the at least one beam splitting element is adapted to split the light beam into at least two separate light beams, and the at least two polarization-sensitive optical elements are arranged such that at least one of the at least two separate light beams passes through one of the polarization-sensitive optical elements, and at least another of the at least two separate light beams passes through another of the polarization-sensitive optical elements.

5. The device according to claim 4, characterized in that A wave plate (41) is arranged in at least one optical path between the beam splitting element (33) and one of the polarization-sensitive optical elements.

6. The device according to claim 1, wherein: The three separate light beams are parallel light beams.

7. The device according to claim 1, characterized in that A wave plate is arranged in at least one optical path between the beam splitting element and one of the three polarization-sensitive optical elements.

8. The device according to claim 1, characterized in that A first wave plate is arranged in the optical path between the beam splitting element and the first polarization-sensitive optical element.

9. The device according to claim 1, characterized in that A second wave plate is arranged in the optical path between the beam splitting element and the second polarization-sensitive optical element.

10. The device according to claim 1, characterized in that No wave plate is arranged in the optical path between the beam splitting element and the third polarization-sensitive optical element.

11. The device according to any one of claims 1 to 5, characterized in that The polarization state control element (27) is arranged in the optical path between the sample (15) and the spectrometer (31).

12. The device according to claim 11, wherein The polarization state control element (27) is arranged between the sample (15) and an entrance slit (51) of the spectrometer (31).

13. The device according to any one of claims 1 to 5, characterized in that At least one beam splitting element is arranged in the optical path between the light source (11) and the sample (15), the beam splitting element being adapted to split a light beam from the light source (11) into at least a first light beam and a second light beam.

14. The device according to claim 13, characterized in that A wave plate is arranged in the optical path of at least the second light beam between the beam splitting element and the sample (15) for generating a polarization-controlled second light beam.

15. The device according to claim 14, in, At least one beam combiner is arranged to combine at least the first beam and the second polarization-controlled beam and to direct the combined beam onto the sample (15).

16. The device according to claim 15, in, At least two spatially separated light spots are generated on the sample (15) in the same focal plane.

17. The device according to claim 13, characterized in that The at least one beam splitting element is adapted to split a light beam from the light source into a first light beam, a second light beam and a third light beam.

18. The device according to claim 17, in, A wave plate is arranged in the optical path of the second light beam between the beam splitting element and the sample (15) for generating a polarization-controlled second light beam.

19. The device according to claim 18, in, Another wave plate is arranged in the optical path of the third light beam between the beam splitting element and the sample (15) for generating a polarization-controlled third light beam.

20. The device according to claim 19, characterized in that At least one beam combiner is arranged to combine the first beam, the polarization-controlled second beam and the polarization-controlled third beam and direct the combined beam onto the sample (15).

21. The device according to claim 20, in, Three spatially separated light spots are generated in the same focal plane on the sample (15).

22. The device according to any one of claims 1 to 5, characterized in that At least one beam combiner is arranged to combine two or more light beams from two or more different light sources and direct the combined light beam onto the sample (15).

23. The apparatus of claim 22, wherein: The combined light beam is directed to separate light spots on the sample (15) located in the same focal plane.

24. The device according to claim 23, characterized in that The light beam from at least one of the light sources is a polarization-controlled light beam.

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