Apparatus and method for raman or fluorescence spectroscopy having instant polarisation analysis

Abstract

The invention relates to an apparatus (100) and method for Raman, photoluminescence or fluorescence spectroscopy. According to the invention, the apparatus comprises an optical device (16) for polarisation splitting and modification, comprising a polarisation splitter (18) and a compensator (17), the optical device (16) being configured and oriented to split the incident light beam (20) emitted onto the diffraction grating (12) into a first part (21) of the emitted light beam that is polarised according to a first polarisation state and a second part (22) of the emitted light beam that is polarised according to a second polarisation state, and the detection system (13) being suitable for receiving, in a first detection zone (14), a spectrum of the first part (21) of the emitted light beam and, simultaneously, in a second detection zone (15), a spectrum of the second part (22) of the emitted light beam.

Description

Apparatus and method for Raman or fluorescence spectrometry with instant polarization analysis technical field

[0001] The present invention relates to the technical field of optical spectrometry instruments and methods for analyzing samples at a microscopic scale. In particular, the present invention relates to analysis and imaging techniques using Raman microspectrometry or fluorescence microspectrometry. Previous technique

[0002] In the above field, confocal Raman microscopy is a well-known analysis and imaging technique, described for example in "Raman Spectroscopy, Review", Paul Rostron, Safa Gaber, Dina Gaber, International Journal of Engineering and Technical Research (IJETR) Vol. 6, No. 1, p. 2454-4698, Sept. 2016. Fluorescence microscopy has many points in common with Raman microscopy.

[0003] In some cases, confocal Raman microscopy uses polarization analysis. Most useful polarization analyses in Raman microscopy involve illuminating the sample with an excitation laser beam polarized according to a polarization state called laser polarization and analyzing the Raman signal according to two polarization states: a polarization state identical to the laser polarization and the orthogonal polarization state.

[0004] Depending on the type of sample being studied and the signal sought (Raman or fluorescence), the laser polarization state is generally one of the following: linear along a fixed direction in the plane of the sample; linear along a direction in the plane of the sample chosen by the user, this direction being identified by an angle; right- or left-hand circular; axial, i.e., along the optical axis of the laser beam incident on the sample; or circumferential. It should be noted that axial and circumferential polarization states are orthogonal to each other. Similarly, right- and left-hand circular polarization states are orthogonal to each other.

[0005] Analyzing the detected signal according to its polarization allows us to extract a quantity such as the degree of polarization, defined as the ratio between the intensity (l_parallel) of the Raman signal polarized according to the The laser polarization and total Raman intensity are given by the following formula: λ_parallel / (λ_perp+λ_parallel), where λ_perp represents the intensity of the Raman signal polarized orthogonally to the laser polarization. The intensity of the polarized Raman signal, λ_parallel and λ_perp respectively, is measured as a function of the Raman wavelength to form a spectrum. This yields a polarization ratio spectrum.

[0006] In the case where the laser polarization is linear and adjustable along an angle theta in the plane of the sample, the analysis of the detected signal according to the polarization allows the quantities l_parallel= f(theta) and respectively l_perp=f(theta) to be extracted as a function of the angle theta and over the range of wavelengths of the detected Raman spectrum.

[0007] In a Raman microspectrometry instrument, controlling the incident laser polarization and the analysis polarization is complicated by the presence of mirrors and / or filters in the path of the laser beam and the Raman signal. However, it is common for the plane of incidence of the light beams on these mirrors and filters to be vertical or horizontal. In this case, a beam with horizontal or vertical linear polarization retains its polarization unchanged during beam transmission. Conversely, a beam with linear polarization oblique to the vertical and horizontal directions, or with elliptical polarization, generally has its polarization modified by the path of the incident laser beam and / or the Raman beam.When the plane of incidence of the light beams on the path is horizontal, a horizontal linear polarization state lies in the plane of incidence and a vertical polarization state is perpendicular to the plane of incidence. Conversely, when the plane of incidence of the light beams on the path is vertical, a vertical linear polarization state lies in the plane of incidence and a horizontal polarization state is perpendicular to the plane of incidence.

[0008] Microspectrometry instruments exist that are suitable for analysis under various polarizations, unaffected by polarization changes that may be introduced along the paths of the laser and / or Raman beam. Such an instrument typically uses a switchable incident laser polarization between horizontal and vertical linear polarization, which is maintained from the laser source to the final reflecting mirror. A compensator, for example a waveplate, is Positioned in the common path of the laser beam and the backscattered Raman beam, this compensator is configured to transform the polarization of the laser light from a transport-conserved polarization (horizontal or vertical) to a polarization of interest on the sample, such as circular polarization or linear polarization oriented at an angle theta in the sample plane. The backscattered Raman beam traveling in the opposite direction undergoes the reciprocal transformation. A fixed polarizer placed in the Raman path, outside the laser beam path, allows selection of one of two transport-unaffected polarization states (parallel or perpendicular linear).

[0009] For circular polarization analysis, according to the prior art, a quarter-wave plate is inserted in the common path. A co-polarization spectrum is obtained by acquiring the Raman spectrum when the polarizer is placed in a configuration parallel to the analysis polarization, and the cross-polarization spectrum when the laser polarization is placed in a configuration orthogonal to the analysis polarization. The ratio of these spectra (or the ratio between one of these spectra and their sum) can be reliably calculated, as they are obtained under directly comparable conditions of Raman intensity analysis.

[0010] To analyze the response under co-polarization and cross-polarization, one solution is to switch one of the polarizations (illumination or analysis) between parallel and perpendicular. However, switching the analysis polarization presents a significant drawback, related to the fact that, generally speaking, spectrometers exhibit a response that varies considerably depending on whether the polarization is parallel or perpendicular. Indeed, spectrometers typically incorporate a diffraction grating. The diffraction efficiency of a grating generally depends strongly on the orientation of the polarization relative to the grating lines. It is therefore not possible to compare the intensities measured experimentally under parallel and perpendicular polarizations. Calibrating the spectrometer's spectral response as a function of polarization is complex.The use of a depolarizer, for example a Lyot depolarizer, proves to be imperfect and unsuitable for Raman spectrometry over a narrow spectral band.

[0011] One of the aims of the invention is to provide an improvement to a Raman microscopy device or, respectively, to a photoluminescence or fluorescence device, enabling the determination of the Raman response or, respectively, of photoluminescence or fluorescence, in a single measurement, according to two mutually orthogonal polarization states, the incident laser polarization being able to be linear along an orientation of the plane chosen by the user, or circular, or circumferential in the plane, or axial along the optical axis of the objective.

[0012] Another object of the invention is to provide an apparatus and a method for Raman microscopy or, respectively, for photoluminescence or fluorescence, enabling an instantaneous and precise measurement of the polarization rate over the spectral range of the Raman spectrum or, respectively, of photoluminescence or fluorescence. Description of the invention

[0013] For this purpose, the invention relates to a Raman or photoluminescence or fluorescence spectrometry apparatus comprising a light source capable of generating an excitation light beam incident on a sample, an optical system for collecting and directing a light beam emitted by the sample towards an inlet of a spectrometer, the spectrometer comprising at least one diffraction grating and a detection system.

[0014] According to the invention, the apparatus comprises an optical polarization splitter and modifier device including a polarization splitter and a compensator, the optical device being disposed on a path of the emitted light beam outside the path of the excitation light beam, the optical device being configured and oriented to separate the emitted light beam incident on the diffraction grating into a first part of the emitted light beam polarized according to a first polarization state and a second part of the emitted light beam polarized according to a second polarization state, the second polarization state being orthogonal to the first polarization state, said first and second polarization states being chosen from polarization states having an SI component of their Stokes vector less than or equal to 0.2 in absolute value and the detection system being adapted to receive, on a first detection zone, a spectrum of the first part of the emitted light beam polarized according to the first polarization state and simultaneously, on a second detection zone, a spectrum of the second part of the emitted light beam polarized according to the second polarization state, the first zone and the second zone being separated along a direction transverse to a spectral diffraction direction on the detection system.

[0015] According to a particular and advantageous aspect, the polarization separator is placed on the path of the light beam emitted downstream of the compensator.

[0016] According to another particular and advantageous aspect, the polarization splitter is arranged on the path of the light beam emitted upstream of the compensator and the compensator presents a Mueller matrix having an element Ml,l less than 0.2 in absolute value over a spectral detection range.

[0017] According to one embodiment, the polarization splitter is able to laterally separate the emitted light beam to form the first part of the emitted light beam and respectively the second part of the emitted light beam.

[0018] For example, the polarization separator includes a birefringent plate or a Savart plate.

[0019] In another embodiment, the polarization splitter is capable of angularly separating the emitted light beam to form the first part of the emitted light beam and respectively the second part of the emitted light beam.

[0020] For example, the polarization splitter includes a Wollaston prism, a Rochon prism, or a Nomarski prism.

[0021] According to a particular and advantageous aspect, the compensator comprises a half-wave plate oriented so that said first polarization state is linear inclined at -45 degrees to the diffraction grating lines and the second polarization state is linear inclined at +45 degrees to the diffraction grating lines, or the compensator comprises a quarter-wave plate oriented so that said first polarization state is right-hand circular and the second polarization state is left-hand circular, or the compensator comprises a Fresnel rhombohedron.

[0022] Advantageously, the compensator exhibits an achromatic retardation on the spectrum of the first part of the emitted light beam, and respectively on the spectrum of the second part of the emitted light beam.

[0023] In various embodiments, the optical beam splitter and polarization modifier is located in the spectrometer between the spectrometer inlet and at least one diffraction grating, or the optical beam splitter and polarization modifier is located in a convergent portion of the light beam emitted upstream of the spectrometer inlet, or the polarization splitter is located in a collimated portion of the light beam emitted upstream of the spectrometer inlet. Advantageously, in this case, the compensator is located downstream of the polarization splitter, the compensator being located between the last optical component capable of modifying the polarization of the light beam emitted along the collimated path and the diffraction grating.

[0024] Advantageously, the optical splitter and polarization modifier device is retractable outside the emitted light beam and the apparatus includes an optical component suitable for insertion in the path of the emitted light beam to compensate for defocusing of the emitted light beam at the inlet of the spectrometer or on the spectrometer detection system, when the optical splitter and polarization modifier device is retracted.

[0025] According to a particular and advantageous aspect, the apparatus includes an optical retarder disposed on a common path of the emitted light beam and the excitation light beam, the optical retarder having an optical retardance and being oriented so as to adjust at least one polarization state of the excitation light beam incident on the sample.

[0026] For example, the optical retarder includes a quarter-wave plate, a half-wave plate, a Fresnel rhombohedron, a birefringent plate with adjustable retardance, or a pixelated optical retarder with spatially adjustable retardance.

[0027] In one particular aspect, the device includes a calculator capable of calculating a polarization rate based on the spectrum of the first part of the light beam. emitted polarized according to the first polarization state and the spectrum of the second part of the emitted light beam polarized according to the second polarization state.

[0028] The invention also relates to a Raman spectrometry, photoluminescence, or fluorescence method comprising the following steps: generating and directing an excitation light beam incident on a sample; collecting and directing a light beam emitted by the sample towards an inlet of a spectrometer comprising at least one diffraction grating and a detection system; separating and modifying the polarization of the emitted light beam along an optical path outside the path of the excitation light beam, so as to separate the emitted light beam incident on the diffraction grating into a first part of the emitted light beam polarized according to a first polarization state and a second part of the emitted light beam polarized according to a second polarization state, the second polarization state being orthogonal to the first polarization state.said first and second polarization states being chosen from polarization states having an SI component of their Stokes vector less than or equal to 0.2 in absolute value, and acquiring on a first detection zone of the detection system a spectrum of the first part of the emitted light beam polarized according to the first polarization state and simultaneously acquiring, on a second detection zone, a spectrum of the second part of the emitted light beam polarized according to the second polarization state, the first zone and the second zone being separated along a direction transverse to a spectral diffraction direction on the detection system.

[0029] Of course, the different features, variants and embodiments of the invention can be combined with each other in various ways as long as they are not incompatible or mutually exclusive. Brief description of the drawings

[0030] Furthermore, various other features of the invention become apparent from the attached description made with reference to the drawings which illustrate non-limiting embodiments of the invention and where:

[0031] Figure 1 is a schematic view of a Raman spectrometry, photoluminescence, or fluorescence apparatus as described in this disclosure.

[0032] Figure 2 is a schematic view of an optical polarization splitter and modifier device according to a first example of its embodiment.

[0033] Figure 3 is a schematic view of an optical beam splitter and polarization modifier device according to a second embodiment.

[0034] Figure 4 is a schematic view of an optical splitter and polarization modifier device according to a third embodiment.

[0035] It should be noted that in these figures the structural and / or functional elements common to the different variants may have the same references. Detailed description

[0036] In Figure 1, the spectrometry apparatus 100 includes a light source 1, an optical system comprising mirrors 2, 3 and a microscope objective 4, a filter 6, a focusing optical system 7, and a spectrometer 9. The spectrometer 9 includes an input 8 (e.g., slit or hole type), at least one diffraction grating 12, and a detection system 13. In the example shown in Figure 1, the spectrometer 9 also includes a mirror 11. The spectrometry apparatus 100 includes a computer 30. According to this disclosure, the spectrometry apparatus 100 includes an optical device 16 that splits and modifies polarization. Optionally, the spectrometry apparatus 100 includes an optical retarder 28. According to a variant, the apparatus 100 includes a confocal aperture disposed in an image plane of the sample between the microscope objective 4 and the inlet 8 of the spectrometer to spatially filter the detected signal.

[0037] We will now describe the operation of the spectrometry apparatus 100. An orthonormal coordinate system XYZ is shown. In the example in Figure 1, a sample 5 is placed in a horizontal XY plane, with the normal to the surface of the sample 5 being vertical. The light source 1 comprises, for example, a laser that emits an excitation light beam 10. The excitation light beam 10 has a well-defined wavelength, denoted lambda, for example, 532 nm. Advantageously, the excitation light beam 10 is polarized according to a linear polarization state. parallel or perpendicular to the plane of Figure 1. In some cases, the light source 1 emits a polarized beam, usually linearly. Optionally, the device includes a polarizer 26 arranged in the path of the excitation light beam 10 to linearly polarize the excitation light beam 10 or to orient the polarization state of the excitation light beam 10, preferably parallel or perpendicular to the plane of Figure 1.

[0038] The optical system with mirrors 2 and 3 and the filter 6 are arranged to direct the excitation light beam 10 towards the microscope objective 4. The optical system with mirrors 2 and 3, the filter 6, and the microscope objective 4 are arranged to maintain the polarization state of the excitation light beam 10 between the light source 1, possibly associated with the polarizer 26, and the sample 5. To this end, the normal to the mirrors 2 and 3 and to the filter 6 and the optical axis of the microscope objective 4 are in the plane of incidence. Thus, the polarization state of the excitation light beam 10 is not affected by the transmission of the excitation light beam 10 through the optical system with mirrors 2 and 3, the filter 6, and the microscope objective 4. The microscope objective 4 focuses the excitation light beam 10 onto a point on the sample 5.Advantageously, the optical axis 27 of the microscope objective 4 is parallel to the normal to the surface of the sample 5 at the illuminated point. In this way, the excitation light beam 10 incident on the sample 5 is polarized with a specific linear polarization.

[0039] Optionally, the spectrometer 100 includes an optical retarder 28 located between the last mirror 3 and the microscope objective 4. The operation of this optional optical retarder 28 is described in detail later in this description. We will first describe the operation of the Raman or fluorescence spectrometer in the absence of the optical retarder 28.

[0040] In response to the excitation light beam 10, the sample 5 emits a light beam emitted 20 by Raman effect or photoluminescence (PL) or fluorescence in a spectral range different from the wavelength of the excitation light beam.

[0041] The spectrometry apparatus 100 shown in Figure 1 is in a backscattering configuration. The optical axis of the excitation light beam 10 incident on Sample 5 is parallel to the normal to the surface of sample 5 at the illuminated point. The backscattered emitted light beam 20 propagates in the opposite direction to the excitation light beam 10. In other words, the excitation light beam 10 and the emitted light beam 20 share a portion of their optical path between sample 5 and filter 6. The excitation light beam 10 and the emitted light beam 20 generally have the same polarization state, for example, linear, parallel or perpendicular to the plane of Figure 1.

[0042] Filter 6 separates the emitted Raman, PL, or fluorescence beam from a Rayleigh beam formed by reflection off the sample at the laser's wavelength (λ). Filter 6 is, for example, an injection-rejection filter. Filter 6 may include a narrow-band suppressor filter with steep sides (or a "notch filter") that transmits the emitted Raman, PL, or fluorescence beam while reflecting the Rayleigh beam in a narrow spectral band around the laser's wavelength.

[0043] The focusing optical system 7 receives the emitted light beam 20 and focuses this beam onto the inlet 8 of the spectrometer 9. Advantageously, the microscope objective 4, the mirror 3, the filter 6 and the focusing optical system 7 are arranged and configured to maintain the polarization state of the emitted light beam 20 Raman or PL or fluorescence when this polarization state is linear vertical (along X or Z) or horizontal (along Y).

[0044] As indicated, the spectrometer 9 under consideration is of the diffraction grating type. The spectrometer includes, for example, a planar diffraction grating 12. Alternatively, in a known manner, the spectrometer includes several diffraction gratings, for example, two or three diffraction gratings mounted on a turret for use one at a time. Each diffraction grating is adapted for a particular spectral region, so that a diffraction grating can be selected for analysis in the corresponding particular spectral region. The spectrometer includes, for example, a mirror 11 that reflects the emitted light beam 20 towards the diffraction grating 12. The diffraction grating 12 diffracts the emitted light beam 20 according to the wavelength so as to form a spectrum on the detection system 13. The mirror 11 and the diffraction grating 12 are configured to form a spectral image of the input 8 of the spectrometer 9 on the detection system 13. The detection system 13 includes a spatially resolved imaging detector in two directions, such as, for example, a CCD-type pixel array detector.

[0045] The diffraction grating 12 of the spectrometer 9 is configured so that the grating lines are substantially aligned along a direction 25 which is here perpendicular to the plane of figure 1.

[0046] According to this disclosure, the spectrometry apparatus 100 includes an optical polarization splitter and modifier device 16 arranged in the path of the emitted light beam 20 (Raman, PL, or fluorescence) outside the path of the excitation light beam 10. Generally, the optical polarization splitter and modifier device 16 comprises a polarization splitter 18 and a compensator 17 arranged in series in the path of the emitted light beam 20. Depending on the embodiment, the polarization splitter 18 is placed upstream or downstream of the compensator 17. Figure 1 illustrates different possible locations of the optical polarization splitter and modifier device 16, these locations being identified by the letters C, D, or E, respectively. However, only one optical polarization splitter and modifier device 16 is used.

[0047] According to a first embodiment, the optical device 16, which acts as a beam splitter and polarization modifier, is located inside the spectrometer 9, between the spectrometer inlet and the diffraction grating 12 (location marked by the letter E in Figure 1). In this case, the optical device 16 is inserted along a portion of the path of the emitted light beam 20 where this beam diverges. We describe below several variations of this first embodiment with reference to Figures 2 to 4.

[0048] Figure 2 illustrates a first embodiment where the optical device 16, which serves as both a separator and polarization modifier, is placed inside the spectrometer 9. The components of the apparatus 100 other than the spectrometer are analogous to those described in connection with Figure 1. Therefore, only the part relating to the spectrometer is shown in Figure 2. In this example, the compensator 17 comprises a wave plate, and the polarization separator 18 comprises a Savart plate. The compensator 17 is positioned upstream of the polarization separator 18. More precisely, the compensator 17 This is a half-wave plate. Advantageously, the half-wave plate 17 is achromatic, meaning it exhibits a half-wave optical retardation over a spectral range containing the Raman, PL, or fluorescence wavelength interval under study. As is known, the Savart plate consists of a first plate 18-1 attached to a second plate 18-2.

[0049] The focusing optical system 7 focuses the emitted light beam 20 (Raman, PL, or fluorescence) into a spot 19 at the inlet 8 of the spectrometer 9. The axis 25 of the lines in the diffraction grating 12 is, for example, oriented vertically. Generally, the emitted light beam 20 comprises a linear polarization component parallel to the axis 25 of the lines in the diffraction grating 12 and a linear polarization component perpendicular to the axis 25 of the lines in the diffraction grating 12. These two polarization components are represented by arrows at the spot 19 in Figure 2. The apparatus 100 is configured so that these two polarization components are transported unaltered by the optical components between the last mirror 3 and the inlet of the spectrometer 9.In this first example, the half-wave plate 17 is oriented at an angle of 22.5 degrees relative to the axis 25 of the lines of the diffraction grating 12 or relative to an axis perpendicular to the axis 25 of the lines of the diffraction grating 12. The half-wave plate 17 receives the emitted light beam 20 and rotates its polarization components by 2x22.5 degrees or 45 degrees. Thus, the linear polarization component parallel to axis 25 remains linearly polarized but oriented at +45 degrees to axis 25 of the lines of the diffraction grating 12. Similarly, the linear polarization component perpendicular to axis 25 remains linearly polarized but oriented at -45 degrees to axis 25 of the lines of the diffraction grating 12. As is known, the Savart plate allows the linear polarization component oriented at +45 degrees to be separated laterally from the linear polarization components oriented at -45 degrees.The Savart plate 18 transforms the spot 19 located at the entrance of the spectrometer into two virtual spots 23 and 24, each associated with a different polarization component. Furthermore, the Savart plate is oriented so that the two virtual spots 23 and 24 are separated along the direction parallel to the axis 25 of the lines of the grating 12. At the output of the Savart plate, we thus obtain a first part 21 of the emitted light beam linearly polarized at -45 degrees and a second part 22 of the beam. The emitted light beam is linearly polarized at +45 degrees. The first part 21 and the second part 22 of the emitted light beam propagate parallel to each other towards the diffraction grating 12. The distance S between the first part 21 and the second part 22 of the emitted light beam is determined by construction using the Savart plate. The distance S is equal to the distance between the two virtual spots 23 and 24.

[0050] The diffraction grating 12 simultaneously receives the first part 21 of the emitted light beam, linearly polarized at -45 degrees, and the second part 22 of the emitted light beam, linearly polarized at +45 degrees. The diffraction grating 12 diffracts, according to the wavelength, the first part 21 of the emitted light beam, linearly polarized at -45 degrees, and the second part 22 of the emitted light beam, linearly polarized at +45 degrees, while maintaining the lateral separation between these two beams. The advantage of using linear polarization components at -45 degrees and +45 degrees is that these polarization states are insensitive to the anisotropy of the diffraction grating 12. Consequently, these two polarization components are diffracted on the diffraction grating 12 with equal diffraction efficiency, even if they are not incident on the same areas of the diffraction grating 12.In this way, spectrometer 9 does not change the ratio between the linear polarization components at -45 deg. and +45deg.

[0051] The spectrometer 9 forms a spectral image (or spectrum) of the first part 21 of the emitted light beam, linearly polarized at -45 degrees, on a first zone 14 of the detection system 13. Simultaneously, the spectrometer 9 forms a spectral image (or spectrum) of the second part 22 of the emitted light beam, linearly polarized at +45 degrees, on a second zone 15 of the detection system 13. These two spectra are separated on the detection system by a distance W in a direction parallel to the axis 25 of the lines of the diffraction grating 12. H1, and H2 respectively, denote the full width at half maximum (FWHM) in intensity of the spectrum of the first part 21, and the second part 22 respectively, of the emitted light beam in a direction transverse to the diffraction direction of the spectra. Advantageously, the Savart plate is configured so that the distance W between the two spectra is greater than the FWHM H1, and H2 respectively.The distance W is here. equal to S. In this way, the detection system 13 simultaneously acquires a spectrum of the first part 21 of the emitted light beam, linearly polarized at -45 degrees, and a spectrum of the second part 22 of the emitted light beam, linearly polarized at +45 degrees. Thus, both spectra can be acquired on the same detection system 13, for example, an imaging detector as illustrated in Figure 2. Alternatively, two detector arrays arranged in parallel are used, one array being capable of detecting the first part 21 of the emitted light beam and the other array being capable of detecting the second part 22 of the emitted light beam.

[0052] The two spectra are transmitted to the calculator 30. The calculator 30 is configured to display these two spectra, or to calculate a ratio between the spectrum of the first part 21 of the emitted light beam, linearly polarized at -45 degrees according to the first polarization state, and the spectrum of the second part 22 of the emitted light beam, linearly polarized at +45 degrees. From these two spectra, the calculator 30 can also deduce the degree of polarization of the emitted light beam relative to the component linearly polarized at -45 degrees or +45 degrees. The degree of polarization is equal to the difference in intensity of the two polarization components divided by the sum of these intensities. The Raman micro-spectrometry or fluorescence instrument 100 thus allows for instantaneous polarization analysis of the detected spectra.

[0053] Advantageously, the optical device 16, which acts as a polarization separator and modifier, is retractable. Removing the optical device 16 from the optical path alters the focus of the spectra on the pixelated sensor, which can degrade the spectral resolution of the spectrometer 9. Therefore, according to a variant of the invention, an optical component, such as a lens or meniscus, is inserted to compensate for the defocusing of the spectra when the optical device 16 is retracted. Advantageously, such a focusing correction optical component is mounted on a sliding blade holder attached to the optical device 16, so that either the optical device 16 or the focusing correction optical component is positioned in the optical path.

[0054] An example of an optical device 16, a splitter and polarization modifier, placed inside the spectrometer as illustrated in Figure 2, is given here. We use a Savart slide made of alpha-BBO (or alpha barium borate), with a total thickness of 16mm and a cross-section of 8x8mm 2 A broadband half-wave plate 17 is placed 1 mm upstream of the Savart plate 18. The half-wave plate 17 is oriented so that its natural axis is at 22.5 degrees to the natural axes of the diffraction grating. The Savart plate is oriented to achieve lateral separation parallel to the grating lines. The CCD detector's recoil position is readjusted from 4 to 5 mm to correct a slight focusing error introduced by the Savart plate 18. Two spectra separated by a distance W of approximately 1.1 mm are obtained on the CCD detector.

[0055] Figure 3 illustrates a second embodiment where the optical device 16, which acts as both a beam splitter and a polarization modifier, is also located inside the spectrometer 9. In this second embodiment, the polarization splitter 18 is made of an anisotropic crystalline material, cut along specific directions, and the compensator 17 is made of a half-wave plate, preferably achromatic. The compensator 17 is positioned downstream of the polarization splitter 18. The polarization splitter 18 is configured and oriented so that the linear polarization components parallel and perpendicular to the axis 25 of the diffraction grating lines 12 are the eigenpolarizations of the polarization splitter 18. In other words, the polarization splitter 18 does not modify the linear polarization components parallel and perpendicular to the axis 25 but separates them laterally.At the spectrometer's input 8, two virtual spots 23 and 24 are thus obtained, separated along an axis parallel to the axis 25 of the grating lines. As in the first example, the half-wave plate 17 transforms the linear polarization components parallel, and respectively perpendicular, to the axis 25 into a linear polarization component at -45°, and respectively +45°, with respect to the axis 25 of the grating lines.

[0056] In the same way as in the example illustrated in Figure 2, the optical device 16, which splits and modifies polarization, thus illuminates the diffraction grating 12 with a first part 21 of the emitted light beam linearly polarized at -45 degrees and a second part 22 of the emitted light beam linearly polarized at +45 degrees. The detection system 13 simultaneously acquires a spectrum of the first part 21 of the emitted light beam linearly polarized at -45 degrees. degrees on a first detection zone 14 and a spectrum of the second part 22 of the emitted light beam linearly polarized at +45 degrees on a second detection zone 15. The first detection zone 14 and the first detection zone 14 are separated by a distance W.

[0057] As an example, apparatus 100 is a Raman microscope comprising a spectrometer 9 with a focal length of 300 mm and using a laser source emitting at a wavelength of 532 nm. An optical device 16, a polarization splitter and modifier, is added inside the spectrometer as illustrated in Figure 3. The polarization splitter 18 is a calcite crystal 10 mm thick and with a cross-section of 8 x 8 mm. 2Downstream of the polarization splitter 18, at a distance of 1 mm, a compensator 17 is placed, consisting of a broadband half-wave plate with one eigenaxis oriented at 22.5 degrees to the eigenaxes of the diffraction grating. A lens with a focal length F=500 mm, made of N-BK7 material, is added at a distance of 60 mm from the spectrometer's entrance hole to correct a slight blurring introduced by the splitter. Two spectra are obtained on the CCD detector, separated by approximately W=0.9 mm: the first spectrum relates to linear polarization at -45°, and the second to linear polarization at +45°. The full width at half maximum (FWH1, H2) of each spectrum is unaffected by the polarization splitter.

[0058] Figure 4 illustrates a third embodiment in which the optical device 16, which serves as both a beam splitter and a polarization modifier, is also located inside the spectrometer 9. In this third embodiment, the polarization splitter 18 is made of an anisotropic crystalline material, cut along specific directions, and the compensator 17 is a quarter-wave plate, preferably achromatic. The compensator 17 is positioned downstream of the polarization splitter 18. Alternatively, the polarization splitter 18 is a Savart plate. The polarization splitter 18 is configured and oriented so that the linear polarization components parallel and perpendicular to the axis 25 of the lines in the diffraction grating 12 are eigenpolarizations of the polarization splitter 18.In other words, the polarization splitter 18 does not modify the linear polarization components parallel and perpendicular to the axis 25 but separates them laterally. This results in two virtual spots 23 and 24 separated at the spectrometer input 8. YJ is an axis parallel to axis 25 of the grating lines. Unlike the first two examples, the quarter-wave plate 17 here transforms the linear polarization components parallel, and respectively perpendicular, to axis 25 of the grating lines into a right-handed circular polarization component, and respectively a left-handed circular polarization component on the diffraction grating 12 (represented by curved arrows in Figure 4). In this third embodiment, the optical device 16, which acts as a splitter and polarization modifier, illuminates the diffraction grating 12 with a first portion 21 of the emitted light beam of right-handed circular polarization and a second portion 22 of the emitted light beam of left-handed circular polarization. The advantage of using right-handed and left-handed circular polarization components is that these circular polarization states are insensitive to the anisotropy of the diffraction grating 12.Therefore, these two components of right-hand circular polarization and left-hand circular polarization are diffracted on the diffraction grating 12 with the same diffraction efficiency.

[0059] The spectrometer 9 forms a spectral image of the first part 21 of the emitted right-circularly polarized light beam on a first zone 14 of the detection system 13. Simultaneously, the spectrometer 9 forms a spectral image of the second part 22 of the emitted left-circularly polarized light beam on a second zone 15 of the detection system 13. These two spectra are separated on the detection system by a distance W in a direction parallel to the axis 25 of the lines of the diffraction grating 12. In this way, the detection system 13 simultaneously acquires a spectrum of the first part 21 of the emitted right-circularly polarized light beam and a spectrum of the second part 22 of the emitted left-circularly polarized light beam.

[0060] According to a second embodiment, the optical device 16, which acts as a polarization splitter and modifier, is located outside the spectrometer 9, between the focusing optical system 7 and the spectrometer inlet 8 (location marked by the letter D in Figure 1). In this case, the optical device 16 is inserted along a portion of the path of the emitted Raman, PL, or fluorescence light beam 20, where this beam converges. The optical device 16 may consist of a waveplate 17 and a Savart plate 18, as described in connection with Figure 2, or of a polarization splitter 18 and a waveplate as described in connection with Figure 18. 3 or Figure 4. In this second embodiment, the optical device 16, which acts as a beam splitter and polarization modifier, generates two real spots 23, 24 at the inlet 8 of the spectrometer 9. The optical device 16 is configured so that the two real spots 23, 24 are oriented parallel to the axis 25 of the diffraction grating lines. The shape of the spatial filter at the inlet 8 of the spectrometer 9 is adapted to allow the two real spots 23, 24 to enter the spectrometer 9, be diffracted on the diffraction grating 12, and form two separate spectra on the detection system. A slit-type spatial filter is typically used. The two spectra have polarization states that are orthogonal to each other. Depending on the type of optical device 16 splitter and polarization modifier used, the two real spots 23, 24 and their corresponding spectra are linearly polarized at ±45 deg. or circularly polarized.In the case of an optical device 16 splitter and polarization modifier similar to that described in connection with Figure 2 or 3, the two actual spots 23, 24 and their corresponding spectra have linear polarizations at -45° and +45° respectively. In the case of an optical device 16 splitter and polarization modifier similar to that described in connection with Figure 2 or 3, the two actual spots 23, 24 and their corresponding spectra have right-hand circular and left-hand circular polarization respectively.

[0061] According to a third embodiment, the optical device 16, which acts as a polarization splitter and modifier, is located outside the spectrometer 9. The polarization splitter 18 is selected and configured to angularly separate two orthogonal polarization states, for example, a parallel linear polarization state and a linear polarization state orthogonal to the axis 25 of the lines in the grating 12. In this case, the polarization splitter 18 is inserted along a portion of the path of the emitted Raman, PL, or fluorescence light beam 20, where this beam is collimated (location marked by the letter C in Figure 1). The polarization splitter 18 is, for example, placed between the injection-rejection filter 6 and the focusing optical system 7 at the inlet 8 of the spectrometer 9. Alpha denotes the separation angle of the polarization splitter 18, and F the focal length of the focusing optical system 7.The polarization splitter 18 comprises a Wollaston prism, a Rochon prism, or a Nomarski prism. The polarization splitter 18 thus makes it possible to generate two real spots 23, 24 at the input 8 of the spectrometer 9, having mutually different polarization states. orthogonal. The separation angle alpha is chosen so that the product alpha. F is greater than the full width at half maximum, H1, H2, of a spectrum on the detection system 13 of the spectrometer 9. The polarization splitter 18 is oriented so that the two real spots 23, 24 are separated along a direction parallel to the axis 25 of the grating lines.

[0062] In the third embodiment, the compensator 17 includes a wave plate. The compensator 17 is arranged downstream of the polarization separator 18. For example, the compensator 17 includes a quarter-wave plate oriented at 45 degrees with respect to the axis 25 of the grating lines or a half-wave plate oriented at 22.5 degrees with respect to the axis 25 of the grating lines or to a transverse axis.

[0063] In the third embodiment, the compensator 17 is arranged between the last optical component capable of modifying the polarization of the light beam emitted on the collimated path, such as a mirror or a filter 6, and the diffraction grating 12, i.e. at the location marked by the letter C, D or E in Figure 1. This arrangement makes it possible to transform the linear polarization states parallel and perpendicular to the axis of the grating lines into right and left circular polarization states or into linear polarization states inclined at ±45 deg. with respect to the axis 25 of the grating lines 12 and to separate these orthogonal polarization states on the detection system 13.

[0064] As an alternative to the third embodiment, the compensator 17 includes a Fresnel rhombohedron positioned along a portion of the path of the emitted light beam 20 (Raman, PL, or fluorescence), where this beam is collimated (location marked by the letter C in Figure 1). The Fresnel rhombohedron is configured to exhibit the retardation of a half-wave or quarter-wave plate. Such a Fresnel rhombohedron has the advantage of exhibiting a constant retardation over a wide wavelength range. A Fresnel rhombohedron is a high-performance and less expensive alternative to an achromatic wave plate.

[0065] A half-wave plate oriented at 22.5 degrees, or a quarter-wave plate oriented at 45 degrees, are examples of compensators 17 capable of transforming the polarization states resulting from the polarization separator into other polarization states insensitive to the anisotropy effects of the diffraction grating. More generally, a compensator 17 suitable for placement after the polarization splitter 18 comprises a plate with a Mueller matrix whose element Ml,l is close to 0. More precisely, the absolute value of the element Ml,l of the Mueller matrix of the compensator 17 is less than 0.2 and preferably less than 0.1. That is, if at the input of the compensator 17 we have IV-IH°= 1, at the output of the compensator 17 we have IV-IH ~0, where IV-IH is the difference between the vertically polarized component of the light intensity (along V) and the horizontally polarized component (along H). In other words, the SI component of the Stokes vector of the beams at the output of the compensator 17 is close to zero. In this document, we denote the element Ml,l of the Mueller matrix Mil. Similarly, we denote the element M1,2 of the Mueller matrix M12, and denote the element M1,3 of the Mueller matrix M13.

[0066] In other words, the compensator 17, placed after the polarization splitter 18, has the function of transforming the polarization of the two separated beams, for example into a horizontal linear polarization component (H) and a vertical linear polarization component (V), into two polarized beams for which the diffraction efficiency of the diffraction grating 12 is identical. The transformations into two circular waves (left and right) or into two linear waves at +45° and -45° are just two examples of the transformations that make it possible to obtain this result. In the general case, it is useful to describe the properties of the compensator 17 by certain properties of its Mueller matrix. The Mueller matrix allows a complete description of the polarization transformations made by a component to an incident beam. The polarization properties of a beam are completely described by its Stokes vector (see, for example, publication R.MA Azzam, “Stokes-vector and Mueller-matrix polarimetry,” JOSA A, col 33, p 1396, 2016). The Mueller matrix of a component can be determined experimentally using instruments commonly called a Mueller meter or Mueller ellipsometer. It follows that a compensator 17 can be defined by the properties of its Mueller matrix, both theoretically and experimentally.

[0067] The use in an optical device 16 polarization splitter and modifier according to the invention, of a compensator 17 having a Mueller matrix whose element Ml,l is less than 0.2 in absolute value and preferably less than 0.1, allows the polarization beams V and H respectively coming from the polarization splitter (i.e. with a Stokes vector component of Sl=+1 and Sl=-1 respectively), to be transformed into two beams whose SI component is less than 0.2 in absolute value, and less than 0.1 respectively. This condition is sufficient to establish that these two beams are diffracted with the same efficiency by the diffraction grating 12.

[0068] The required property for the compensator 17 located after the polarization splitter 18 is that the element Ml,l of its Mueller matrix be zero or at least less than 0.2, and preferably less than 0.1. A quarter-wave plate oriented at 45 deg, or a half-wave plate oriented at 22.5 deg, are examples of compensators satisfying the property Ml,l=0. In the case of a microscope operating with several laser wavelengths, and therefore several Raman (or photoluminescence or fluorescence) wavelength ranges, the condition on the element Mil < 0.2 in absolute value (and preferably Mil < 0.1) of the Mueller matrix is ​​less limiting than a constraint on a broadband quarter-wave plate or a broadband half-wave plate.The use of a compensator with an Ml,l matrix close to 0 is desirable because it allows, with less cost and less complexity, to obtain the same diffraction efficiency on the diffraction grating over the spectral band of interest.

[0069] We describe here another example of a compensator whose Mueller matrix element Ml,l is close to zero over a wide spectral band. In practice, we choose a compensator whose Mueller matrix element Ml,l is less than 0.2 in absolute value, and preferably less than 0.1, over the spectral band of interest. Compensator 17 is made by connecting two 540 nm half-wave plates in series, the first half-wave plate oriented at 15 degrees from the vertical, the second half-wave plate oriented at 35 degrees from the vertical, in the order in which the light beam emitted 20 passes through compensator 17 on face A, the opposite face being face B. When this compensator 17 is illuminated on its face A with light polarized such that its reduced Stokes vector is (1,0,0), that is, with horizontal linear polarization, we experimentally determined the vector The output Stokes vector is (Mil; M12; M13). It is observed that the output Stokes vector has a nearly zero Mil component, with Mil less than 0.1 over the spectral band extending from 400 nm to 1000 nm. At wavelengths close to 530 nm, the component behaves almost like a half-wave plate oriented at 22.5°; the horizontal linear polarization is transformed into a linear polarization at 45°, and we have M11=0, Abs(M12)=1, and M13=0. However, at 425 nm and around 725 nm, the behavior is close to that of a quarter-wave plate oriented at 45°, since the output Stokes vector is approximately that of a circular polarization, Abs(M13)=1, and M11=M12=0. Between wavelengths of 425 nm and 725 nm, the horizontal polarization is transformed into various elliptical polarizations, the equivalent behavior of the component is not that of a half-wave or quarter-wave plate.When this compensator 17 is illuminated on its face B with light polarized such that its reduced Stokes vector is (1,0,0), i.e., with horizontal linear polarization, the output Stokes vector, (Mil, M12, M13), has been experimentally determined. It is observed that the property of Mil being close to zero is verified, with Abs(M11) less than 0.1 over a wide spectral range from 400 nm to 1000 nm. However, the output polarization is strongly dependent on the wavelength.

[0070] As mentioned above, the spectrometry apparatus 100 optionally includes an optical retarder 28 positioned between the last mirror 3 and the microscope objective 4 along a portion of the path shared by the excitation light beam and the emitted light beam 20 from the sample. In this portion of the optical path, the excitation light beam 10 is collimated. The optical retarder 28 exhibits optical retardation and is oriented to modify the polarization state of the excitation light beam 10 incident on the sample 5.

[0071] In a first example, the optical retarder 28 comprises a half-wave plate with the wavelength of the excitation light beam 10. This half-wave plate is oriented at 45 degrees to the linear polarization axis of the excitation light beam, to rotate the polarization direction of the excitation light beam 10 by 90 degrees and transform a parallel linear polarization into a perpendicular linear polarization and vice versa. Alternatively, the half-wave plate is oriented at an angle theta between 0 and 45 degrees with respect to the linear polarization axis of the beam excitation light, to rotate the polarization direction of the excitation light beam 10 by a double angle (2x theta).

[0072] In a second example, the optical retarder 28 includes a Fresnel rhombohedron with a half-wave retardance (or lambda / 2) and orientable at an angle theta between 0 and 45 degrees relative to the linear polarization axis of the excitation light beam.

[0073] In a third example, the optical retarder 28 includes a quarter-wave plate, at the wavelength lambda of the excitation light beam 10. This quarter-wave plate is oriented at a fixed angle of ±45 degrees with respect to the linear polarization axis of the excitation light beam, to transform the linear polarization state of the excitation light beam 10 into a right- or left-hand circular polarization state on the sample.

[0074] In another example, the optical retarder 28 comprises a birefringent plate having a retardance that can be adjusted and / or oriented relative to the plane of incidence on the sample. In yet another example, the optical retarder 28 comprises a pixelated optical retarder having a spatially adjustable retardance.

[0075] The optical retarder 28 is therefore positioned on a collimated portion of the path of the emitted light beam 20. The optical retarder 28 performs the reciprocal polarization transformation of the transformation performed on the laser polarization. Conversely, the optical retarder 28 transforms the polarization state of the emitted light beam 20 from the sample into a polarization state that is preserved by transport via the mirror 3 and the filter 6, to the optical device 16, which acts as a separator and polarization modifier.

[0076] It is useful to consider an imperfect optical retarder 28. Indeed, there are optical retarders 28 with a quarter-wave or half-wave retardation that are perfect at a given wavelength. However, these properties are generally only approximate over a wide wavelength range. Now, according to this disclosure, the optical retarder 28 operates both at the laser wavelength and at Raman, PL, or fluorescence wavelengths, respectively, which are different. In addition, a number of Raman microscopes have several lasers at different wavelengths.

[0077] The optical retarder 28 in the common path is chosen to exhibit a relatively stable optical retardation (e.g., half-wave or quarter-wave) across a wide wavelength range, from the laser wavelength up to the longest wavelength commonly observed in Raman, PL, or fluorescence microscopy. For example, if the laser emits at a wavelength of 532 nm, and the useful Raman spectrum extends up to 650 nm, a waveplate is chosen whose optical retardation is optimal around the central wavelength of 585 nm.

[0078] In certain applications, it can be useful to observe the Raman response to excitations with polarizations more complex than linear or circular. This disclosure describes placing a spatially inhomogeneous optical retarder 28 in the common path. Such a non-uniform optical retarder 28 is, for example, a pixelated retarder or a vortex retarder. Using such a spatially inhomogeneous optical retarder 28 allows the Raman response to be measured along the excitation mode and orthogonally to the excitation mode in a single operation.

[0079] Device 100 allows control of the optical timer 28, to perform different measurements as chosen by the user.

[0080] Thus, the user can perform angularly resolved measurements in linear polarization, by placing a half-wave plate 28 in the common path, and acquiring spectral measurements as a function of the orientation of the half-wave plate.

[0081] These results can be represented as polar diagrams at different wavelengths. They can also be represented as the polarization degree spectrum, that is, the intensity along one polarization divided by the sum of the intensities of the two orthogonal polarizations detected. Alternatively, the results can be represented as the ratio of the intensities of the two orthogonal polarizations detected.

[0082] In another application, the user can perform circularly polarized measurements by placing a quarter-wave plate 28 in the common path, and measuring The two spectra correspond to right and left circular polarization. These results can be represented as a ratio between the two spectra relating to cross-polarization and co-polarization.

[0083] Of course, various other modifications can be made to the invention within the scope of the attached claims.

Claims

Claims Raman or photoluminescence or fluorescence spectrometry apparatus (100) comprising a light source (1) capable of generating an excitation light beam (10) incident on a sample (5), an optical system (3, 4, 6, 7) for collecting and directing a light beam emitted (20) by the sample towards an inlet (8) of a spectrometer, the spectrometer (9) comprising at least one diffraction grating (12) and a detection system (13), characterized in that the apparatus comprises an optical device (16) splitter and polarization modifier comprising a polarization splitter (18) and a compensator (17), the optical device (16) being disposed on a path of the emitted light beam (20) outside the path of the excitation light beam (10),the optical device (16) being configured and oriented to separate the emitted light beam (20) incident on the diffraction grating (12) into a first part (21) of the emitted light beam polarized according to a first polarization state and a second part (22) of the emitted light beam polarized according to a second polarization state, the second polarization state being orthogonal to the first polarization state, said first and second polarization states being chosen from polarization states having an SI component of their Stokes vector less than or equal to 0.2 in absolute value and the detection system (13) being adapted to receive, on a first detection zone (14), a spectrum of the first part (21) of the emitted light beam polarized according to the first polarization state and simultaneously, on a second detection zone (15),a spectrum of the second part (22) of the emitted light beam polarized according to the second polarization state, the first zone (14) and the second zone (15) being separated along a direction transverse to a spectral diffraction direction on the detection system (13). Apparatus according to claim 1 in which the polarization separator (18) is disposed in the path of the emitted light beam downstream of the compensator (17). Apparatus according to claim 1 in which the polarization separator (18) is disposed in the path of the emitted light beam upstream of the compensator (17) and in which the compensator (17) has a Mueller matrix having an element Ml,l less than 0.2 in absolute value over a spectral detection range.

4. Apparatus according to any one of claims 1 to 3 in which the polarization splitter (18) is able to laterally split the emitted light beam (20) to form the first part (21) of the emitted light beam and respectively the second part (22) of the emitted light beam.

5. Apparatus according to claim 4 in which the polarization separator (18) comprises a birefringent plate or a Savart plate (18-1, 18-2).

6. Apparatus according to any one of claims 1 to 3 in which the polarization separator (18) is able to angularly separate the emitted light beam (20) to form the first part (21) of the emitted light beam and respectively the second part (22) of the emitted light beam.

7. Apparatus according to claim 6 in which the polarization splitter (18) comprises a Wollaston prism, a Rochon prism or a Nomarski prism.

8. Apparatus according to any one of claims 1 to 7 wherein the compensator (17) comprises a half-wave plate oriented such that said first polarization state is linear inclined at -45 degrees to the lines of the diffraction grating (12) and the second polarization state is linear inclined at +45 degrees to the lines of the diffraction grating (12), or wherein the compensator (17) comprises a quarter-wave plate oriented such that said first polarization state is right-hand circular and the second polarization state is left-hand circular, or wherein the compensator (17) comprises a Fresnel rhombohedron.

9. Apparatus according to any one of claims 1 to 8 in which the compensator (17) exhibits an achromatic retardation on the spectrum of the first part (21) of the emitted light beam, and respectively on the spectrum of the second part (22) of the emitted light beam.

10. Apparatus according to any one of claims 1 to 9, wherein the optical device (16) polarization splitter and modifier is disposed in the spectrometer (9) between the inlet (8) of the spectrometer and at least one diffraction grating (12), or wherein the optical device (16) polarization splitter and modifier is disposed in a convergent portion of the light beam emitted (20) upstream of the inlet of the spectrometer, or wherein the polarization splitter (18) is disposed in a collimated portion of the A light beam emitted (20) upstream of the spectrometer inlet, wherein the compensator (17) is disposed downstream of the polarization splitter (18), the compensator (17) being disposed between the last optical component capable of modifying the polarization of the emitted light beam along the collimated path and the diffraction grating (12). An apparatus according to any one of claims 1 to 10, wherein the optical device (16) polarization splitter and modifier is retractable from the emitted light beam, and wherein the apparatus (100) comprises an optical component adapted to be inserted in the path of the emitted light beam to compensate for a defocusing of the emitted light beam at the inlet of the spectrometer (9) or on the detection system (13) of the spectrometer (9), when the optical device (16) polarization splitter and modifier is retracted.An apparatus according to any one of claims 1 to 11 comprising an optical retarder (28) disposed in a common path of the emitted light beam (20) and the excitation light beam (10), the optical retarder (28) having an optical retardation and being oriented so as to adjust at least one polarization state of the excitation light beam (10) incident on the sample. An apparatus according to claim 12 wherein the optical retarder (28) comprises a quarter-wave plate, a half-wave plate, a Fresnel rhombohedron, a birefringent plate having an adjustable retardation, or a pixelated optical retarder having a spatially adjustable retardation.An apparatus according to any one of claims 1 to 13 comprising a calculator (30) capable of calculating a polarization ratio based on the spectrum of the first portion (21) of the emitted light beam polarized according to the first polarization state and the spectrum of the second portion (22) of the emitted light beam polarized according to the second polarization state. A Raman spectrometry, photoluminescence, or fluorescence method comprising the following steps: generating and directing an excitation light beam (10) incident on a sample (5), collecting and directing a light beam emitted (20) by the sample (5) towards an inlet (8). of a spectrometer (9) comprising at least one diffraction grating (12) and a detection system (13), separate and modify the polarization of the emitted light beam (20) along an optical path outside the path of the excitation light beam (10), so as to separate the emitted light beam (20) incident on the diffraction grating into a first part (21) of the emitted light beam polarized according to a first polarization state and a second part (22) of the emitted light beam polarized according to a second polarization state, the second polarization state being orthogonal to the first polarization state, said first and second polarization states being chosen from polarization states having an SI component of their Stokes vector less than or equal to 0,2 in absolute value and acquire on a first detection zone (14) of the detection system (13) a spectrum of the first part (21) of the emitted light beam polarized according to the first polarization state and simultaneously acquire, on a second detection zone (15) a spectrum of the second part (22) of the emitted light beam polarized according to the second polarization state, the first zone (14) and the second zone (15) being separated along a direction transverse to a spectral diffraction direction on the detection system (13).

Images