Backscatter laser spectrometry device having multiple measurement points and associated measurement method

Abstract

The invention relates to a backscatter laser spectrometry device (1) comprising a laser source (30), an optical focusing system (50), an optical separator (60), and a spectrometer (80). According to the invention, the spectrometry device comprises a beam splitter (40) arranged on an optical path of the source light beam upstream of the optical separator, wherein the optical focusing system is arranged and configured to focus a first and a second secondary excitation light beam (402, 404) onto a first and a second measurement point (202, 204), respectively, wherein the optical focusing system is adapted to collect a first and a second backscattered light beam (412, 414), respectively, wherein the optical separator is adapted to direct the first and the second backscattered light beams toward a first and a second point (822, 824) at the entrance of the spectrometer, respectively, and wherein the spectrometer directs the first and the second backscattered light beams onto a first and a second zone (842, 844) on the multichannel detector, respectively.

Description

MULTI-POINT LASER BACKSCATTERING SPECTROMETRY DEVICE AND ASSOCIATED MEASUREMENT METHOD TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates generally to a laser spectrometry device.

[0002] It relates more specifically to a backscatter laser spectrometry device adapted to simultaneously perform two measurements of backscattered spectra at two spatially separated measurement points and their separate reading.

[0003] The invention finds a particularly advantageous application in the simultaneous measurement of a spectrum generated by Raman scattering and / or by fluorescence, and / or by photoluminescence, in backscattering for a sample of interest and for a reference body, the latter being used for calibration purposes.

[0004] It also relates to a measurement process using this laser spectrometry device. STATE OF THE ART

[0005] In this document, laser spectrometry means the spectroscopic analysis of a light beam emitted by a sample exposed to an excitatory laser beam, the light beam being emitted either by Raman effect, by fluorescence or photoluminescence, or by nonlinear optical effect, such as coherent Raman scattering, which includes techniques such as coherent anti-Stokes Raman scattering (CARS), or stimulated Raman scattering (SRS).

[0006] Raman spectroscopy, in particular, is a widespread analytical technique in industry, for carrying out online process monitoring operations, or for routine analyses in a laboratory, or even in a research and development context.

[0007] This spectroscopy technique is based on Raman scattering, where, following the excitation of a sample (which may correspond to a pure substance, or to a mixture) in solid, liquid, or gaseous state, by a laser, a Raman spectrum representative of / specific to the sample is emitted by it, and before being detected by a spectrometer, then analyzed.

[0008] The excitation laser preferentially emits monochromatic light radiation, which corresponds to the excitation line v e .

[0009] The sample excited by the laser emits a beam containing one or more Raman lines. n v2, v3, which are specific to it and which make up its Raman spectrum. These Raman lines v1, v2, v3 can be described by a frequency position (usually indicated as a wavenumber, denoted cm⁻¹). -1 ), a width, and an intensity.

[0010] This beam can be detected by backscattering, that is, in the same direction as the exciting laser. For example, it can be detected on a spectrometer equipped with a multichannel detector, capable of recording all the spectral information necessary for analysis when a dispersive element, such as a grating, allows the light beam to be decomposed into a spectrum.

[0011] The frequency position of the Raman lines of the excited sample is measured by subtracting it from that of the excitation line v e This is indeed the frequency shift relative to this excitation line v e which is measured. Thus, if spectral fluctuations shift the frequency of the excitation line by an amount Av e The frequency position of the Raman lines emitted by the sample shifts by the same amount Av e .

[0012] It is therefore necessary to carefully follow the exact spectral position of the excitation line v e , in order to accurately calibrate the Raman spectrum of the sample studied, and thus guarantee the reliability of the analyses performed.

[0013] To achieve this, the state of the art proposes to establish a reference spectrum, for example by transmission through a reference sample, preferably a pure substance, whose Raman spectrum is well known, and not subject to variations.

[0014] For example, document FR2841984 discloses such a method and the associated device, where a reference spectrum is produced under conditions identical to those of the sample of interest, and then detected by the same Raman spectrometer. To achieve this, a fraction of the laser intensity is diverted to the reference sample and measured either after transmission through the reference sample or after reflection from the reference sample.

[0015] However, since the optical paths traveled by the different Raman spectra during detection are identical, the Raman spectra from the sample of interest and the reference sample are detected superimposed in the spectrometer and thus coincide at the same position of the multichannel detector. This complicates the choice of the reference sample, as it requires either sequential measurements of the reference sample and the sample to be analyzed, or the selection of chemical species with distinct lines from the Raman lines of the sample of interest when the two spectra are spatially superimposed and measured simultaneously. PRESENTATION OF THE INVENTION

[0016] In order to remedy the aforementioned drawback of the prior art, the present invention proposes a laser backscatter spectrometry device with multiple measurement points.

[0017] More specifically, the invention proposes a backscatter laser spectrometry device comprising a laser source emitting a source light beam, an optical focusing system, an optical splitter, a spectrometer comprising an input and a multichannel detector, and a processing unit, in which it is provided: - a beam splitter arranged on an optical path of the source light beam upstream of the optical separator, the beam splitter being adapted to divide the source light beam into a first secondary excitation light beam propagating along a first optical path and a second secondary excitation light beam propagating along a second optical path, - the optical splitter being arranged on the first optical path and on the second optical path, the optical splitter being adapted to simultaneously direct the first secondary excitation light beam and the second secondary excitation light beam towards the focusing optical system, - the optical focusing system being arranged and configured to focus the first, respectively second, secondary excitation light beam onto a first, respectively second, measurement point, the first measurement point being spatially separated from the second measurement point, - the optical focusing system being adapted to collect a first, respectively second, backscattered light beam emitted by the first, respectively second, measurement point, propagating in the opposite direction to the first, respectively second, secondary excitation light beam following the first, respectively second, optical path to the optical separator, - the optical splitter being adapted to direct the first, respectively second, backscattered light beam, towards a first, respectively second, point of the spectrometer inlet, the first point of the spectrometer inlet being spatially separated from the second point of the spectrometer inlet, - the spectrometer being adapted to direct the first, respectively second, backscattered light beam onto a first, respectively second, zone of the multichannel detector, the processing unit being adapted to deduce a first spectrometry signal acquired on the first zone and a second spectrometry signal acquired on the second zone.

[0018] Thus, thanks to the invention, the simultaneous acquisition of several signals, for example two spectrometry signals, in particular, two spectra from two distinct spatial regions of a sample, is made possible. Distinguishing the two spectrometry signals is also facilitated by reading from two separate regions of the multichannel detector. It is therefore possible to acquire a spectrum from a reference of calibration, and a sample of interest. Advantageously, thanks to the reading on two distinct regions of the multichannel detector, the choice of a suitable calibration reference is facilitated. Indeed, it is no longer necessary for the lines of the reference spectrum to be non-superimposed on the lines of the spectrum of the sample of interest.

[0019] Other advantageous and non-limiting features of the multi-point laser backscatter spectrometry device according to the invention, taken individually or in all technically possible combinations, are as follows: - The beam splitter is a prism. - The beam splitter is a fiber coupler comprising an input adapted to inject the source light beam, a first fiber output branch adapted to propagate the first secondary exciter light beam and a second fiber output branch adapted to propagate the second secondary exciter light beam. - The beam splitter is a diffraction grating. - the focusing optical system comprises a first focusing optical system placed on the first optical path traveled by the first secondary excitatory light beam and a second focusing optical system placed on the second optical path traveled by the second secondary excitatory light beam, the first focusing optical system and the second focusing optical system having different optical properties. - The first optical focusing system and the second optical focusing system have focal lengths of different values. - The first secondary excitatory light beam and the second secondary excitatory light beam have distinct polarization states from each other. - The laser backscatter spectrometry device includes a reference sample on which the second measurement point is located and in which the second backscattered beam serves as a calibration reference for the first backscattered beam.

[0020] The invention also relates to a laser backscatter spectrometry method, in which a measurement and / or analysis of at least one sample is carried out simultaneously at a first measurement point and a second measurement point, the laser backscatter spectrometry method comprising the following steps: - division, by a beam splitter arranged on an optical path, of a source light beam into a first secondary excitation light beam following a first optical path and a second secondary excitation light beam following a second optical path, - simultaneous direction of the first secondary excitation light beam and the second secondary excitation light beam towards a focusing optical system using of an optical splitter arranged on the first optical path and the second optical path, - focusing by the optical focusing system of the first, respectively second, secondary excitation light beam onto a first, respectively second measurement point, the first measurement point being spatially separated from the second measurement point, - collection by the optical focusing system of a first, respectively second, backscattered light beam emitted by the first, respectively second, measurement point, propagating in the opposite direction to the first, respectively second, secondary excitation light beam, following the first, respectively second, optical path, - separation by the optical splitter of the first, respectively second, backscattered light beam originating from the first, respectively second, secondary excitation light beam, and of the first, respectively second secondary excitation light beam, - direction, by an optical injection system, of the first, respectively second, backscattered light beam, towards a first, respectively second point of an input of a spectrometer, said first, respectively second point being spatially separated from each other, - direction by the spectrometer of the first, respectively second, backscattered light beam onto a first, respectively second zone of a multichannel detector, - simultaneous reading by a processing unit of a first, respectively second, spectrometry signal acquired on the first, respectively second zone, and representative of the first measurement point and the second measurement point of the sample.

[0021] Another advantageous and non-limiting feature of the laser backscattering spectrometry method according to the invention is that the spectrometry signal can be a Raman spectrum or a fluorescence spectrum or a photoluminescence spectrum.

[0022] 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. DETAILED DESCRIPTION OF THE INVENTION

[0023] The description that follows, with regard to the attached drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be carried out.

[0024] Regarding the attached drawings:

[0025] Figure 1 is a schematic view of a backscatter laser spectrometry device according to a first embodiment of the present disclosure, comprising a laser source, an optical focusing system, a multichannel detector and a beam splitter comprising a birefringent prism;

[0026] Figure 2 schematically represents a variant of the first embodiment, comprising several measurement channels.

[0027] Figure 3 is a schematic view of a second embodiment of a backscatter laser spectrometry device, where the beam splitter includes a fiber coupler;

[0028] Figure 4 is a schematic view of a third embodiment of a backscatter laser spectrometry device, where the beam splitter includes a diffraction grating;

[0029] Figure 5 is a schematic view of a variant of a backscatter laser spectrometry device according to the first embodiment, comprising two optical focusing systems of different focal lengths.

[0030] Figure 6 is a schematic view of a second variant of the backscatter laser spectrometry device according to the first embodiment, comprising a polarization splitter plate. First method of implementation

[0031] Figure 1 schematically represents a backscatter laser spectrometry device 1, capable of performing measurements and / or analyses on a sample 2 of interest.

[0032] This backscatter laser spectrometry device 1 is for example suitable for measurements on a sample 2 of micrometric dimensions, and it is then a laser micro-spectrometry device.

[0033] The sample 2 to be measured may also be of macroscopic size and / or located at a distance from the backscatter laser spectrometry device 1.

[0034] The backscatter laser spectrometry device 1 is described first, followed by a description of a measurement method for performing a measurement and / or analysis by laser spectrometry on at least one sample 2 by this device.

[0035] As schematically represented in Figure 1, the backscatter laser spectrometry device 1 comprises a laser source 30, a beam splitter 40, a focusing optical system 50, a separating element 60, an injection optical system 70, a spectrometer 80, and a processing unit 90.

[0036] These various elements included in the backscatter laser spectrometry device 1 are possibly integrated within the same housing, or grouped into blocks, for example according to their function, the blocks then being arranged at a distance from each other from the others, in separate cases. Here, the different possible cases are not shown.

[0037] The laser source 30 emits a light beam 302, which is emitted either continuously or pulsed. Here, the example of a continuously emitting laser source is advantageously considered.

[0038] The laser source 30 under consideration includes, but is not limited to, a solid-state laser, a dye-sensitized laser, a gas laser, or a laser diode. In the embodiment described in Figure 1, the laser source 30 is a diode-pumped solid-state laser. This solid-state laser is then coupled to a suitable fiber, for example, a single-mode fiber or a multimode fiber with a core diameter of 50 microns and a numerical aperture (NA) of 0.22.

[0039] For Raman scattering applications, the laser source 30 advantageously emits a monochromatic light beam 302 in the form of a line in the frequency domain. This line is defined by a central position and a width, for example, measured at half-height of a line intensity. Alternative definitions of the line width are nevertheless possible.

[0040] To say that the light beam from source 302 is monochromatic is equivalent to saying that the laser source 30 is spectrally pure, meaning that its spectrum does not contain any spurious lines or spectral bands emitted outside of a main emission line. Furthermore, this main emission line has a small linewidth. Here, the linewidth is less than 30 gigahertz.

[0041] The light beam from source 302 has a wavelength, denoted  e , for example, of 532 nanometers. However, a wavelength Âe between 400 nanometers and 1064 nanometers, is also conceivable within the framework of this disclosure, optical elements adapted in terms of bandwidth are then used.

[0042] This light beam source 302 has a luminous power P e at the output of the laser source 30, usually varying from a few milliwatts to a few watts, depending on the samples 2 to be analyzed and the laser spectrometry technique used. More specifically, here, the light beam from the source 302 has an optical power or luminous power P e equal to 100 mW.

[0043] Furthermore, this light beam source 302 can be polarized or unpolarized. Here, preferably, the light beam source 302 is unpolarized or polarized in a linear polarization state. This polarization state, in particular its orientation, can be controlled using retarder plates and / or a polarizer, not shown here.

[0044] Two principal axes of polarization are represented on the light beam Source 302, using notations known to those skilled in the art. The first principal axis of polarization lies in the plane of Figure 1 and is represented by a double arrow. The second principal axis of polarization is perpendicular to the plane of Figure 1 and is represented by a circled point.

[0045] The source light beam 302 is directed towards sample 2. A wavelength-shifted light signal specific to sample 2 is generated within sample 2 through light-matter interaction processes, such as Raman scattering, photoluminescence, fluorescence, or any other light-matter interaction process deemed appropriate. For the purposes of this disclosure, the light signal emitted by sample 2 is then detected by backscattering, i.e., in the same direction as the source light beam 302 used for excitation. This is also referred to as epi-detection. The generated light signal and the source light beam 302 are thus counter-propagating, meaning they propagate in the same direction but in opposite directions.In order to detect the light signal generated alone, a separating element 60 is placed on the optical path common to the generated light signal and the source light beam 302, so as to separate the light signal generated on sample 2 from the source light beam 302. For example, the separating element 60 is configured here to transmit the generated light signal, and reflect the source light beam 302.

[0046] The optical path followed by the source light beam 302 to sample 2 is usually called the "excitation path," while the path followed by the light signal generated by sample 2 to the spectrometer 80 is called the "detection path." These two paths are partially overlapped. Here, they overlap between the beam splitter 60 and sample 2 and are separated by the beam splitter 60.

[0047] The assembly formed by the excitation channel and the detection channel is designated as the measurement channel 10.

[0048] In order to describe the arrangement of the different elements included in the laser backscatter spectrometry device 1, their placement and order according to the direction of propagation of the light from the laser source 30 is detailed below, starting with the excitation path, from the laser source 30 to the sample 2. The direction of propagation of the light beams is also indicated by arrows, as is customary.

[0049] According to Figure 1, an optical collimation system 32 collimates the source light beam 302 emitted by the laser source 30. This optical collimation system has, for example, a focal length of 11 millimeters. Thus, in the case of a multimode fiber with a core diameter of 50 microns and a numerical aperture, denoted NA, of 0.22, the source light beam 302 has a diameter of approximately 5 millimeters. The diameter The beam is defined here at the "waist" or neck of the beam and a divergence angle of approximately 4 milliradians. The diameter here corresponds to the diameter where the distribution of beam irradiance in the transverse plane is equal to 1 / e 2 , where e is equal to Napier's constant.

[0050] According to other examples, the light beam source 302 can also already be collimated at the output of the laser source 30, thus making the optical collimation system 32 shown here unnecessary.

[0051] The source light beam 302 propagates along an optical path, referred to as the source light beam optical path, towards the sample 2 to be analyzed. For this purpose, the source light beam 302 is guided by plane mirrors 34, 36. The exact number of reflecting mirrors, as well as their positioning along the source light beam optical path, particularly their angle of incidence relative to this optical path, is left to the discretion of those skilled in the art. Here, two plane mirrors 34, 36 are used on the source light beam optical path, preferably with a reflectivity ratio for the excitation wavelength λ. e greater than or equal to 90%, for example 98%, the % sign representing a percentage.

[0052] A beam splitter 40, for example a prism, is suitable for angularly splitting an incident beam. This prism corresponds, for example, to a Rochon or Wollaston prism. A Rochon or Wollaston prism comprising an assembly of birefringent prisms, here two in number, is placed in the optical path of the source light beam 301. The beam splitter 40 thus separates the source light beam 302 into several secondary excitation beams, here two in number: a first secondary excitation light beam 402 and a second secondary excitation light beam 404.

[0053] Other embodiments using different types of optical elements as beam splitter 40 are described later in the description.

[0054] This beam splitter 40 is placed at a chosen distance from the collimation optical system 32; in particular, here, these two elements are arranged close to each other, which offers greater compactness to the backscatter laser spectrometry device 1. For example, the collimation optical system 32 and the beam splitter are here separated by a few millimeters to a few centimeters.

[0055] Luminous power P e the source light beam 302 can be distributed equally between the secondary excitation beams, or according to any other ratio suitable for the needs of the measurement and / or analysis of sample 2.

[0056] Thus, the beam splitter 40 separates the source light beam 302 into a first secondary exciter light beam 402, which propagates along a first optical path, and a second secondary exciter light beam 404, propagating along a second optical path spatially distinct from the first optical path.

[0057] In other words, the first secondary excitation light beam 402 and the second secondary excitation light beam 404 both propagate towards sample 2, but respectively follow the first and second optical paths, which are distinct from each other. The excitation path is therefore divided into two disjoint sub-paths.

[0058] Here, in Figure 1, these secondary excitation beams 402, 404 propagate at an angle of, for example, 1.5 degrees. Alternatively, a smaller angle, such as 1 degree, or conversely, a larger one, for example, 10.6 degrees, or even 20 degrees between the secondary excitation beams 402, 404 is also possible, depending on the beam splitter 40 considered.

[0059] The advantage of a relatively small angle, for example 1.5 degrees, between the secondary excitation beams 402 and 404, is to avoid excessive divergence between them. In this way, the secondary excitation beams 402 and 404 can pass through common optical elements, thus limiting the number of optical elements and reducing cost and / or size.

[0060] Thus, the secondary excitation beams 402, 404 propagate in a generally weakly divergent direction, even over distances on the order of a few tens of centimeters, for measurements on macroscopic samples, and rather on the order of a few centimeters, for example over 250 millimeters in the context of a micro-spectrometry device.

[0061] In the embodiment illustrated in Figure 1, the beam splitter 40 comprises a Rochon prism that separates the incident source light beam 302 into two secondary excitation beams 402 and 404, also called the ordinary beam and the extraordinary beam. This separation is based on the polarization of the incident source light beam 302. Indeed, due to birefringence—that is, the dependence of the refractive indices of a medium on the polarization of the incident beam—the source light beam 302 is refracted along two possible optical paths, which are spatially distinct from one another.

[0062] The ordinary beam and the extraordinary beam also have polarization states orthogonal to each other. For example, the first secondary exciter beam 402 is linearly polarized along a direction contained in a plane of Figure 1, while the second secondary exciter beam 404 is polarized orthogonally to this direction, along a direction pointing out of the plane of Figure 1. Thus, the first secondary exciter beam 402 has vertical polarization, and the second secondary exciter beam 404 has as for it, a horizontal polarization.

[0063] Here, in the embodiment considered, the source light beam 302 is linearly polarized at 45 degrees with respect to one of the optical axes of the two birefringent prisms composing the Rochon prism. This choice of polarization state and orientation for the source light beam 302 allows for an even distribution of the luminous power P e between the ordinary beam and the extraordinary beam, and therefore between the first secondary exciter light beam 402 and the second secondary exciter light beam 404. In other words, half of the luminous power P e is redistributed in the first secondary exciter light beam 402, the other half of the light power P e is distributed in the second secondary exciter light beam 404.

[0064] However, other choices of state and polarization orientation of the source light beam 302 with respect to optical axes specific to the Rochon prism are possible, and allow a person skilled in the art to adjust the distribution of the light power P e in an appropriate manner.

[0065] Thus, using a Rochon prism made of magnesium fluoride (MgF2), with a thickness of 35 mm, an angle of 1.5 degrees can be obtained between the ordinary beam and the extraordinary beam.

[0066] Similarly, using a Rochon prism made of yttrium vanadate (YVo4), with a thickness of 12 mm, an angle of 10.6 degrees can be obtained between the ordinary beam and the extraordinary beam.

[0067] The choice of material, its thickness and the angle between the first excitatory light beam 402 and the second secondary excitatory light beam 404 is made by a person skilled in the art, according to the spatial arrangement of the backscatter laser spectrometry device 1, taking into account for example the distance between the beam splitter 40 and the sample 2.

[0068] A possible variant, not shown here, uses a Wollaston prism as a beam splitter 40. The principle of beam splitting based on the polarization of the incident beam from a Wollaston prism is approximately the same as for the Rochon prism. However, for a Wollaston prism, the first secondary excitation light beam 402 and the second secondary excitation light beam 404 form a symmetrical angle with respect to the optical axis of the source light beam 302.

[0069] In the case of a Wollaston prism, an angle close to 1 degree of separation between the two secondary excitation beams 402, 404 is obtained using a prism with a thickness of 2 microns of quartz.

[0070] Alternatively, it is also possible to obtain a 20-degree angle between the two secondary excitation beams 402, 404 using a Wollaston prism with a thickness of 2.3 microns of calcite.

[0071] An optical splitter 60, located downstream of the beam splitter 40, relative to the direction of light propagation from the laser source 30, is arranged so that a normal to its surface forms an angle of approximately 45 degrees with respect to the first and second optical paths. This optical splitter 60 is therefore suitable for reflecting the secondary excitation light beams, here the first secondary excitation light beam 402 and the second secondary excitation light beam 404, towards sample 2.

[0072] In practice, this optical splitter 60 is, for example, a dichroic mirror which, for a given angle of incidence, reflects a certain spectral range of wavelengths and transmits another spectral range of wavelengths. Thus, it is possible to separate the secondary excitation light beams 402, 404, at the excitation wavelength A e, other beams of light of different wavelengths.

[0073] Here, in the detailed embodiment, the optical separator 60 is a dichroic filter of the "high-pass" type with an angle of incidence approximately equal to 45 degrees, and capable of reflecting the excitation wavelength  e associated with the secondary excitation light beams 402, 404. Thus, the optical splitter 60 here has a cutoff wavelength strictly greater than the excitation wavelength  e emitted by the laser source 30. In the example presented, the cutoff wavelength is therefore strictly greater than 532 nanometers. Specifically, it is equal to 532.8504 nanometers.

[0074] Finally, an optical focusing system 50 focuses the secondary exciter light beams 402, 404 onto as many spatially distinct measurement points 202, 204 on the sample 2. Here, given the distance between the beam splitter 40 and the angle of 1.5 degrees between the secondary exciter light beams 402, 404, the latter are separated by 6.5 millimeters from each other at the level of the optical focusing system 50.

[0075] In this first described embodiment, the focusing optical system 50 comprises a single element, placed both on the first optical path and the second optical path along which the first, respectively the second, secondary exciter light beam 402, 404 propagates.

[0076] The choice of optical properties for this focusing optical system 50 depends on the configuration and context of the laser spectrometry measurement. For example, in a laser microspectroscopy setup, the focusing optical system 50 consists of a microscope objective or a lens. Alternatively, if the backscattering laser spectroscopy setup described 1 is intended to investigate macroscopic samples, for example, on a process Online, a lens of appropriate focal length can be chosen by a person skilled in the art. Also, and not limited to, the focusing optical system 50 can also consist of a microlens array, each microlens being centered on one of the optical paths of the secondary excitation light beams 402, 404.

[0077] The 50 focusing optical system has a focal length, denoted f1 / in figure 1, the value of which is chosen according to the desired distance between sample 2 and the focusing optical system 50.

[0078] Furthermore, the 50 focusing optical system also possesses other properties, particularly concerning the geometry of its optical surfaces. The selection of these surfaces, based on the need for correction of optical aberrations, for example, is left to the discretion of a person skilled in the art.

[0079] In the described embodiment, the lens has a focal length f' = 18 millimeters and a diameter of 12 millimeters, though these values ​​are not limiting. The diameter of the focusing optical system 50 is chosen to collect both beams of interest. Here, the first secondary excitation light beam 402 and the second secondary excitation light beam 404, whose centers are 6.5 millimeters apart and each has a diameter of 5 millimeters, are collected by the focusing optical system 50.

[0080] The sample 2 to be analyzed is of diverse nature, for example a powder, a deposit, a liquid, a gas, a mixture etc. The observation of the sample 2 is therefore carried out through different containers, possibly placed on a sample holder 20 attached or not to the backscattering laser spectrometry device 1.

[0081] For example, sample 2 may be contained in a measuring cell including at least one window for a flowing fluid, be placed between a microscope slide and coverslip for a biological sample, or take the form of a wafer (also called a "slice"), simply placed on the sample holder 20, etc.

[0082] Here, in Figure 1, sample 2 is placed on a sample holder 20.

[0083] The focusing system 50 focuses the secondary exciter light beams 402, 404 into as many measurement points 202, 204.

[0084] In the described embodiment, the first secondary excitatory light beam 402 is focused by the focusing optical system 50 into a first measuring point 202. Similarly, the second secondary excitatory light beam 404 is focused into a second measuring point 204.

[0085] Here, the distance between measurement points 202, 204 in the sample plane depends on the angle between the secondary excitation light beams 402, 404 and the focal length f1 / of the focusing optical system 50. Here, given the parameters of the embodiment presented, that is to say a focal length of 18 millimeters, and a angle between secondary excitation light beams 402, 404 of 1.5 degrees, the first measurement point 202 and the second measurement point 204 are separated by approximately 500 microns.

[0086] Sample 2, here unique, is placed so that measurement points 202, 204 coincide with a plane of the sample.

[0087] Through light-matter interaction, a light spectrometry signal, called spectrometry signal 902, 904, is generated by each of the measurement points 202, 204. This spectrometry signal 902, 904 is representative of the physico-chemical properties of the associated measurement point 202, 204.

[0088] For example, in the case of a laser spectrometry device in backscattering 1 by Raman scattering, it is a Raman spectrum that is emitted from each of the measurement points 202, 204. The Raman spectrum emitted by each of the measurement points 202, 204 contains Raman lines representative of the physico-chemical properties of the sample(s) 2 located at the level of these measurement points 202, 204. In this case, the Raman spectrum constitutes the spectrometry signal 902, 904.

[0089] Thus, according to this disclosure, a first 902 spectrometry signal and a second 904 spectrometry signal are generated simultaneously, in parallel with each other.

[0090] Different arrangements of measurement points 202, 204 are possible. Here, in Figure 1, the first measurement point 202 is located at sample 2, while the second measurement point 204 is located on the sample holder 20. Measurement points 202, 204 can also both be located on sample 2, or, in the context of an online process, the first measurement point 202 is located upstream of the process, while the second measurement point 204 is located downstream of the process.

[0091] For ease of language, for these different possible arrangements, the first and second measurement points 202, 204 are designated as being on sample 2, or equivalently as being in the plane of the sample.

[0092] The backscatter laser spectrometry device 1 may optionally include a multi-axis translation stage, not shown in Figure 1, on which the sample holder 20 is placed, so as to be able to scan the measurement points 202, 204.

[0093] Advantageously, these various possible arrangements allow for measurements and / or analyses at two spatially distinct measurement points 202, 204, simultaneously in time. Thus, the spectrometry signals 902, 904 can advantageously be compared with each other during measurement and / or analysis.

[0094] To facilitate this comparison, or simplify the measurement and / or analysis of these spectrometry signals 902, 904, it is important to maintain a spatial distinction between spectrometry signals 902, 904 from distinct measurement points 202, 204.

[0095] The detection path, also called the collection path, associated with the optical paths of the spectrometry signals 902, 904 from sample 2 to spectrometer 80 is now described.

[0096] The focusing optical system 50 used for focusing is used again, this time to collect the spectrometry signal 902, 904 from each of the spatially distinct measurement points 202, 204.

[0097] The spectrometry signal 902, 904 emitted by a measurement point 202, 204 is for example emitted in a solid angle of An steradian.

[0098] The backscatter laser spectrometry device 1 shown here collects this spectrometry signal 902, 904 from each of the measurement points 202, 204 in a backscatter configuration, i.e. in a direction forming an angle of 180 degrees with respect to the secondary excitation light beam 402, 404.

[0099] Thus, in the embodiment shown in Figure 1, a first backscattered light beam 412 emitted by the first measuring point 202, and a second backscattered light beam 414 emitted by the second measuring point 204 are collected by the focusing optical system 50.

[0100] Depending on the distance of the measurement point 202, respectively 204 from the optical axis of the focusing optical system 50, each of the backscattered light beams 412, respectively 414 is collimated with a certain angle.

[0101] According to Fermat's principle, the first, and second, backscattered light beams 412 and 414 respectively, propagate along the first, and second respectively, optical path. As a reminder, these first and second optical paths are spatially distinct. Here, they form an angle of 1.5 degrees with respect to each other.

[0102] In other words, the first, respectively second, backscattered light beam 412, 414 is counter-propagating with respect to the first, respectively second, secondary exciter light beam 402, 404, and propagates along the same first, respectively second, optical path, up to the optical separator 60 described previously.

[0103] The optical splitter 60 separates the excitation path and the collection path. Like the excitation path, the collection path is subdivided into as many sub-paths as there are backscattered light beams 412, 414.

[0104] As described previously, the optical splitter 60 separates the two paths, reflecting and / or transmitting certain spectral ranges, which include wavelengths of the different beams involved in the light-matter interaction. In particular, if a backscatter laser spectrometry device 1 uses scattering Raman is considered, the optical separator 60 notably allows the rejection of a Rayleigh beam formed by elastic scattering (called Rayleigh scattering) on ​​sample 2, and which is at the excitation wavelength  e emitted by the laser source 30.

[0105] Alternatives to the separation method, such as the use of a semi-reflective plate, by placing a series of optical filters on the detection path, are left to the discretion of the person skilled in the art.

[0106] In the embodiment illustrated in Figure 1, the backscattered light beams 412, 414 are transmitted through the optical separator 60, to an optical injection system 70.

[0107] Optionally, an attenuating optical element 65, such as a polarizing filter or a neutral density filter, is inserted between the optical injection system 70 and the optical splitter 60. This attenuating optical element 65 is used to control the light intensity of the backscattered light beams 412, 414. Advantageously, the use of a polarizing filter, for example, an analyzer, allows for the selective attenuation of the light intensity of one of the backscattered light beams 412, 414 relative to the other. Indeed, it should be recalled that in this first embodiment, where the beam splitter 40 is a birefringent prism, the backscattered light beams 412, 414 have orthogonal polarization states. It is thus possible to selectively attenuate the light intensity of one of these two beams.

[0108] This optical injection system 70 receives the first backscattered light beam 412 and the second backscattered light beam 414, which are spatially distinct and not collinear with each other. The optical injection system 70 focuses the different backscattered light beams onto an input 82 of the spectrometer 80. Here, the optical injection system 70 has, for example, a focal length of 33 millimeters.

[0109] Here, the inlet 82 is, for example, a rectangular slit. In this case, it is a direct beam coupling spectrometer, also known as free beam coupling.

[0110] In the case of a so-called "fiber" spectrometer 80, the input 82 corresponds to a bundle of optical fibers 83, where several optical fibers are arranged within a single ferrule. These optical fibers are adapted to propagate the various injected backscattered light beams 412, 414.

[0111] Since the backscattered light beams 412, 414 are not collinear, the optical injection system 70 focuses the first backscattered light beam 412 to a first point 822 and the second backscattered light beam 414 to a second point 824, spatially distinct from the first point 822 on the inlet 82 of the spectrometer 80. Advantageously, the points 822, 824 resulting from the different backscattered light beams 412, 414 and focused by the optical injection system 70 are arranged in a line. Given the focal length of the injection optical system 70, the first 822 and the second point 824 are about 900 microns apart at the inlet 82.

[0112] In the case of a direct beam coupled spectrometer 80, the line formed by the points 822, 824 is for example oriented in the same direction as a principal length of the slit constituting the entrance 82 of the spectrometer 80.

[0113] By orienting the slit of the inlet 82 along a top-to-bottom axis, noted HB1 in figure 1, the optical injection system 70 focuses the different backscattered light beams according to positions of different heights H1, H2.

[0114] Alternatively, if the spectrometer 80 is fiber-optic, the optical fibers of the optical fiber bundle 83 are arranged to couple points 822 and 844. In particular, if a two-fiber optical bundle, denoted a "2:2" optical fiber bundle, is used, the two optical fibers are placed approximately 900 microns apart. It is thus possible to couple the first backscattered light beam 412 to one of the two optical fibers, and to couple the second backscattered light beam 414 to the other of the two optical fibers.

[0115] The spectrometer 80 under consideration is, for example, a diffraction grating spectrometer 80. The spectrometer 80 thus includes a planar diffraction grating, not shown in Figure 1. Alternatively, in a known manner, the spectrometer 80 comprises several diffraction gratings, for example, two or three diffraction gratings mounted on a turret for use one at a time.

[0116] The diffraction grating of the spectrometer 80 then receives the backscattered light beams at different heights and diffracts them at an angle dependent on the wavelength, so as to form the spectrometry signal 902, 904, typically a spectrum, such as a Raman spectrum, on areas 842, 844 of a multichannel detector 84.

[0117] This multichannel detector 84 is shown in Figure 1. It is a spatially resolved imaging detector in two directions, such as, for example, a pixel array detector of the CCD type. Here, the multichannel detector 84 has, for example, a dimension of 5 millimeters in a top-to-bottom direction, corresponding to an HB2 axis.

[0118] The diffraction grating of spectrometer 80 has lines, which are aligned along the HB axis, so as to diffract the backscattered light beams 412, 414 along a perpendicular axis, noted GD2.

[0119] Thus, on the multichannel detector 84, spectral information is read on the GD2 axis of the pixel matrix, corresponding to an accumulated charge value representative of the intensity of the backscattered light beam as a function of wavelength, and spatial information, indicating the measurement point 202, 204 on the sample 2 is read on the HB2 axis.

[0120] Here, according to the illustrated embodiment, the first spectrometry signal 902, from the first measurement point 202 and the second spectrometry signal 904, from the second measurement point 204 are read on two spatially distinct areas 842, 844.

[0121] The vertical spacing of the first zone 842 and the second zone 844 on detector 84 is chosen so as to avoid crosstalk between the first spectrometry signal 902 and the second spectrometry signal 902.

[0122] Here, due to the spectral dispersion of the first, and of the second backscattered light beam 412, 414 by the diffraction grating of the spectrometer 80, the first zone 842 and the second zone 844 is rectangular in shape, as shown in Figure 1.

[0123] Reading the spectrometry signals 902, 904 on two distinct zones 842, 844, here by their height H11, H22, on the axis HB2 of the multichannel detector 84, therefore facilitates, advantageously, the possible comparison of the measurements and / analyses carried out on two spatially distinct measurement points 202, 204 on sample 2.

[0124] In particular, thanks to this disclosure, one of the measurement points, here, for example, the second measurement point 204, can be used as a calibration reference for measurements and / or analyses carried out on the first measurement point 202. This calibration reference has the advantage of being recorded under similar experimental conditions, and simultaneously in time.

[0125] For example, this calibration reference is a sample 2 whose optical response to excitation by the laser source 30 is well known to the person skilled in the art and / or calibrated prior to measurement and / or analysis.

[0126] In particular, it is known to use the substrate, for example silicon or glass, of sample 2 as a calibration reference, or for example a pure substance of predetermined composition and concentration.

[0127] Furthermore, advantageously, the polarization states used for the measurement and / or analysis of the first measurement point 202 and the second measurement point 204 are orthogonal to each other, which provides a complementary measurement and / or analysis in terms of polarization response, carried out under similar experimental conditions, and simultaneously.

[0128] Spectrometry signals 902, 904, here in the form of Raman spectra for example, and from a first, respectively second measurement point 202, 204 are represented on the pixel matrix of the multichannel detector 84 in Figure 1. The intensity information is translated here schematically on Figure 1 so as to directly represent a spectrum, and not intensity levels.

[0129] The multichannel detector 84 is controlled by a processing unit 90; this processing unit 90 enables, in particular, the reading of the spectrometry information obtained on the pixel matrix of the multichannel detector 84.

[0130] Thus, in this first embodiment, the second spectrometry signal 904 obtained on the second height H22 of the multichannel detector 84 and read by the processing unit 90 may have been calibrated in wavelength and / or intensity. In other words, wavelength calibration means that a correspondence is determined between the spectral information read on the GD2 axis of the pixel matrix of the multichannel detector 84 and the theoretical wavelength, for example, of a given spectral line. Similarly, intensity calibration consists of establishing a correspondence beforehand between, in the case of a multichannel detector 84 in the form of a CCD camera, a charge value accumulated for each pixel at a given spectral position and the light power used for the light-matter interaction.

[0131] Thus, this detailed knowledge of the calibration reference response as a function of experimental conditions allows the second spectrometry signal 904 recorded on the second measurement point 204 to be used to accurately determine the spectral information and / or its intensity contained in the first spectrometry signal 902; this first spectrometry signal 902 originates from the first measurement point 202, ideally located at the level of the sample 2 of interest.

[0132] The fact that the first spectrometry signal 902 and the second spectrometry signal 904 are obtained and read on respectively a first height H11 and a second height H22 of the multichannel detector 84, these not being spatially coincident, facilitates the distinct reading of the information from each of the measurement points 202, 204.

[0133] Alternatively, only the intensity information within a restricted spectral window may be of interest for measurement and / or analysis. This spectral window could, for example, be centered on a line in the specific spectrum of sample 2. In this case, the intensity information within this restricted spectral window can be selected upstream of the spectrometer 80 using a set of appropriate optical filters, and spectral dispersion by the spectrometer 80's diffraction grating is unnecessary. The intensity information from each of the measurement points 202, 204 can then be read pointwise on two areas 842, 842, considered as point features of the multichannel detector 84.

[0134] Advantageously, the first embodiment described, where the source light beam 302 is divided by the beam divider 40 into two beams of orthogonal polarization, allows the study of a sample 2 of interest to be completed by a polarization analysis.

[0135] Indeed, by adding a polarization analyzer 66 upstream of the inlet 82 of the spectrometer 80 relative to the direction of light propagation, it is possible to to focus on the polarization of the spectrometry signal 902, 904. For example, the polarization analyzer 66 is placed here between the possible attenuating optical element 65 and the injection optical system 70. Such a polarization analyzer 66 corresponds in practice to a polarizer, adapted to select a preferred polarization direction. This preferred polarization direction is usually defined by an axis.

[0136] Furthermore, the fact that the first secondary excitation light beam 402 and the second secondary excitation light beam 404 are polarized according to two orthogonal polarization states allows us to study the response of sample 2 of interest following simultaneous excitation according to these two polarization states. Advantageously, the use of two orthogonally polarized beams reduces the time required to analyze the polarization response of sample 2.

[0137] Thus, if we consider a laser spectrometry device using Raman backscattering 1, where the spectrometry signals 902, 904 correspond to Raman spectra, the addition of the polarization analyzer 66 allows us to investigate the polarization orientation of the resulting Raman spectrum, particularly the polarization orientation of the Raman lines. Specifically, by maintaining a given orientation for an axis of the polarization analyzer 66, a simultaneous measurement of a spectrum corresponding to excitation with horizontal polarization and a spectrum corresponding to excitation with vertical polarization allows us to determine the depolarization rate for the different lines contained in the Raman spectrum of a given sample 2.

[0138] Figure 2 shows a variant of the first embodiment. Here, rather than a single measurement channel 10, as described previously, several measurement channels 10 are connected to an input 82 of the spectrometer 80.

[0139] This variant is notably compatible with a fiber-optic 80 spectrometer.

[0140] The surface of the multichannel detector 84 is then divided into regions 8431, 8432, 8433, 8434, 8435. Here, five regions are considered on the multichannel detector 84. Each of these regions 8431, 8432, 8433, 8434, 8435 is associated with a measurement channel 10.

[0141] Thus, here are five routes regions 8431, 8432, 8433, 8434, 8435 which correspond to five measurement routes 10.

[0142] These different measurement paths 10 each correspond, for example, to the same embodiment, or on the contrary, may correspond to different embodiments.

[0143] Each of the regions 8431, 8432, 8433, 8434, 8435 associated with a measurement channel comprises a zone 842 and a zone 844, on which a first spectrometry signal 902 and a second spectrometry signal 904 are respectively collected. As detailed previously, these two spectrometry signals 902, 904 are emitted by two distinct measurement points 202, 204, generated on the sample by a beam splitter 40.

[0144] On each of these measurement channels 10, a beam splitter 40 separates a source light beam into two secondary excitation light beams 402, 404, which, once focused on the sample, generate the two spectrometry signals 902, 904. For a given measurement channel 10, these two spectrometry signals 902, 904 are each collected on an optical fiber input 8221, 8241, 8225, 8245.

[0145] The set of optical fibers 830, 831, 838, 839 is then arranged according to a bundle of optical fibers 83, in order to spatially organize the measurement channels 10 relative to each other on the surface of the multichannel detector 84.

[0146] The five measurement channels 10 in Figure 2 thus represent five pairs of spectrometry signals 902, 904, these signals being collected on five pairs of optical fiber inputs 8221, 8241, 8225, 8245.

[0147] The ten optical fibers 830, 831, 838, 839 are then assembled at the inlet 82 of the spectrometer 80 according to a bundle of optical fibers 83, that is to say that the ten optical fibers 830, 831, 838, 839 are then held together, and are here arranged in a line at the end located at the inlet 82 of the spectrometer 80. This line, here made up of ten optical fibers 830, 831, 838, 839, is oriented according to the orientation of the elongated direction of the slit of the inlet 82.

[0148] Once diffracted by, here, a planar diffraction grating, the spectrometry signals 902, 904 from each of the measurement channels 10, are collected on distinct heights of the multichannel detector 84.

[0149] This variant advantageously allows reading 902, 904 spectrometry signals from different measurement channels on the same multichannel detector, thus exploiting the available surface area by parallelizing several measurements.

[0150] This variant is also compatible with other embodiments, as described later in the description. Second embodiment

[0151] A second embodiment for the backscatter laser spectrometry device 1 is shown in Figure 3.

[0152] In this second embodiment, the laser source 30 is at least partially fiber-laden, and the source light beam 302 propagates within a suitable optical fiber 31.

[0153] The beam splitter 40 consists here of an optical fiber coupler, connecting a fiber input to several fiber output branches. In the embodiment shown in Figure 3, two fiber output branches are represented. It is therefore a "1x2", "1:2", or "Y" fiber coupler, according to various terminologies. in use. In this case, the optical fiber coupler has a diameter of 100 pm and a numerical aperture, denoted NA, of 0.22.

[0154] One end of the optical fiber 31, in which the source laser beam 302 propagates, is connected to the fiber input of the optical fiber coupler. Two optical fibers are connected to each of the fiber output branches, so that the first secondary excitation light beam 402 propagates within one of the optical fibers connected to one of the fiber output branches, and the second secondary excitation light beam 404 propagates within the second optical fiber connected to the second fiber output branch.

[0155] The two optical fibers carrying the first secondary excitation light beam 402 and the second secondary excitation light beam 404 are then joined side-by-side within an optical fiber ferrule 33, which acts as a connector. The two optical fibers connected to the two output branches of the optical fiber coupler are grouped onto a single connector and are separated by a specific distance. This separation distance is adjusted according to requirements. Furthermore, the ends of the two optical fibers are oriented so that their optical axes form a non-zero angle with each other.

[0156] The optical fiber coupler distributes the light power P e of the source light beam 302 according to a ratio defined by the construction parameters of such an optical fiber coupler. For example, a 50:50 ratio allows for an even distribution of the light power P eof the source light beam 302 between the first secondary exciter light beam 402 and the second secondary exciter light beam 404. Other ratios are also possible, depending on the targeted applications.

[0157] The first and second secondary excitation light beams 402 and 404, respectively, are each collimated by a collimating optical system 32, so that the beams propagate in free space to the optical splitter 60, described previously, and reflect the excitation beams back towards sample 2. The separation distance and the angle of the optical fiber ends on the connector define, in particular, a divergence angle between the first secondary excitation light beam 402 and the second secondary excitation light beam 404 after their collimation by the collimating optical system 32, which here corresponds to a lens. The divergence angle depends, in particular, on the distance between the two cores of the optical fibers, as well as the focal length of the lens of the collimating optical system 32.

[0158] For example, the two optical fibers are arranged side by side, one against the other. In this case, the two fiber cores are separated by the thickness of a cladding surrounding each fiber.

[0159] Alternatively, the two fibers can be separated from each other. the other, in order to increase the distance between the two fiber cores, for example, according to a desired divergence angle.

[0160] In practice, a typical distance between two optical fiber cores is between 50 micrometers and a few millimeters. This distance is measured from the geometric center of one fiber core to the geometric center of a core in a second optical fiber.

[0161] The lens of the collimation optical system 32, for its part, has a focal length varying between 4 millimeters and 18 millimeters, for example.

[0162] Thus, the divergence angle, that is to say the angle measured between the first secondary exciter light beam 402 and the second secondary exciter light beam 404, varies between approximately 0.16 degrees and 37 degrees.

[0163] In particular, here, this lens of the collimation optical system 32 has a focal length of 5 millimeters.

[0164] Thus, if a 1.5-degree angle is desired between the two beams, given the focal length of the collimation optical system 32, a separation distance of 130 microns is required, for example. These proposed values ​​are by no means limiting; the separation distance can be modified due to a desired angle between the first secondary excitation light beam 402 and the second secondary excitation light beam 404, for example.

[0165] In particular, a separation distance of 500 microns between the output branches of the optical fiber coupler can also be proposed.

[0166] The first, respectively second, secondary exciter light beam 402, 404 then propagate along the first, respectively second optical path, to the focusing optical system 50, as described previously for the first embodiment.

[0167] The focusing optical system 50 then generates two measurement points 202, 204 spatially distinct from each other, by focusing the secondary excitation beams 402, 404 on the sample 2. In practice, the focusing optical system 50 images the cores of the optical fibers, assumed to be point-like, on the sample 2.

[0168] Here, the focusing optical system 50 takes the form of a focusing lens. For example, this is a lens with a focal length of 18 millimeters. The alternative solutions proposed previously remain possible.

[0169] In the same way as in the first embodiment, the spectrometry signals 902, 904 generated on sample 2 and originating from the two distinct measurement points 204, 204 are collected by the same focusing optical system 50, and the backscattered light beams 412, 414 propagate along the first optical path and the second optical path towards the optical splitter 60, where they are transmitted to spectrometer 80, in a manner similar to the first embodiment.

[0170] Thus, an optical injection system is placed so as to focus the backscattered light beams 412, 414 at the level of the inlet 82 of the spectrometer 80. The latter has, for example, a fiber coupling or a free-space coupling, as described previously.

[0171] For example, considering a fiber-coupled spectrometer 80, the injection optical system 70 couples the secondary excitation beams 402, 404 into a fiber bundle. Such a fiber bundle has an organized arrangement of at least as many optical fibers as there are secondary excitation beams 402, 404, and therefore as many as there are backscattered light beams 412, 414. For example, here two optical fibers are used to collect the backscattered light beams 412, 414 coupled to them by the injection optical system 70. This is therefore a "2:2" optical fiber bundle as described previously.

[0172] The optical injection system 70 reimages the cores of the optical fibers originating from the beam splitter 40 onto the optical fiber bundle. The core diameters of the optical fibers composing the optical fiber bundle are thus chosen to suit the collection of these images.

[0173] The backscattered light beams 412, 414 collected at the inlet 82 of the spectrometer 80 are then diffracted by a diffractive element, for example a planar diffraction grating, so as to form the spectrometry signal 902, 904, for example, a Raman spectrum on areas 842, 844 of the multichannel detector 84.

[0174] As described previously, and as illustrated by Figure 2, it is possible to parallelize measurements from several measurement channels 10 on the same multichannel detector 84. For this, the surface of this multichannel detector 84 is divided into several regions 8431, 8432, 8433, 8434, 8435, each of these regions 8431, 8432, 8433, 8434, 8435 being associated with two spectrometry signals 902, 904 emanating from the same measurement channel 10.

[0175] For each of the measurement channels 10, the spectrometry signals 902, 904 from a first measurement point 202 and a second measurement point 204 are collected by a bundle of optical fibers 83.

[0176] This optical fiber bundle 83 has an input 85, where optical fibers 830, 831, 838, 839 are grouped into as many pairs as there are measurement channels 10.

[0177] Thus, for a measurement channel 10, the signals from the first measurement point 202 and the second measurement point 204 are collected on a pair of optical fibers 830, 831, 838, 839.

[0178] The entire set of optical fibers 830, 831, 838, 839 of the optical fiber bundle 83 is then arranged at the inlet 82 of the spectrometer 80, in order to organize the paths of measures them relative to each other on the surface of the multichannel detector 84. Third mode of implementation

[0179] A third embodiment is described in connection with Figure 4. Here, the beam splitter 40 is a diffraction grating (according to Anglo-Saxon terminology) in reflection or transmission.

[0180] For example, in the case of a reflection diffraction grating, as shown in Figure 4, after collimation of the source light beam 302 emitted by the laser 30, the beam splitter 40 angularly separates the source light beam 302 into a multitude of secondary excitation light beams 402, 404 having the same wavelength as the source light beam 302. Here, each of these secondary excitation light beams 402, 404 corresponds to a diffracted beam of the source light beam 302 by the reflection diffraction grating. Each diffracted beam is deflected at its own specific angle relative to the source light beam 302, each angle corresponding to a diffraction order.In the case where a first and a second secondary excitation light beam 402, 404 are considered, the first secondary excitation light beam 402 corresponds, for example, to the beam diffracted by the beam splitter 40 of order zero, while the second secondary excitation light beam 404 corresponds to the diffracted beam of order one. Equivalently, the first secondary excitation light beam 402 and the second secondary excitation light beam 404 each correspond to any two orders of the diffraction grating, as long as these orders are distinct.

[0181] In particular, the orders selected for the secondary exciter light beams 404, 402 are for example chosen according to a desired angle, given a fixed focal length for the focusing optical system 50 and a distance between the beam splitter 40 and the sample 2.

[0182] Similarly, the angle of incidence of the light beam source 302 on the beam splitter 40 is chosen according to the desired angle. The value of this angle is chosen, for example, based on the desired distance between the measurement points 202 and 204 and / or based on constraints related to the dimensioning of the various components of the device.

[0183] For example, in the embodiment shown in Figure 4, we consider a focusing optical system 50 with a focal length of 40 millimeters, corresponding more particularly to a microscope objective with a magnification of x5. Such an objective has, for example, a field of view of 4.4 millimeters, with a pupil diameter of 12 millimeters.

[0184] In this case, it may be desirable to have two measurement points 202 and 204 separated from each other by a distance, for example, equal to 3.3 millimeters, in order to maximize the distance between the two measurement points 202, 204 relative to the field of view of the microscope objective as described in the previous paragraph.

[0185] With such a spacing between the two measurement points 202, 204, it is possible to obtain two spectrometry signals 902, 904 associated with areas of distinct chemical compositions within the same field of view.

[0186] Alternatively, two samples 2 are placed side by side under this microscope objective, with the first measurement point 202 located on one of the two samples, while the second measurement point 204 is located on the other of the two samples. For example, these two samples are here arranged on the same sample holder 20.

[0187] Such an arrangement of the samples is obviously compatible with the other embodiments presented in this description.

[0188] To obtain such spacing on the sample using the focusing optical system 50, which here has a focal length of 40 millimeters, it is therefore advantageous to have a separation angle between the first secondary excitatory light beam 402 and the second secondary excitatory light beam 404 equal to at least 4.7 degrees.

[0189] Here, in order to achieve such a separation angle between the secondary excitation beams 402 and 404, a diffraction grating with 100 lines per millimeter is chosen as the beam splitter 40. The diffraction plane of this grating is the plane shown in Figure 4. An angle of incidence between the source light beam 302 and the surface of the diffraction grating is chosen to be 52 degrees. This angle of incidence is defined as a positive angle between a normal to the surface of the diffraction grating and the source light beam 302. With this configuration, the zeroth-order beam from the diffraction grating is reflected at -52 degrees to the normal, according to Snell's law of reflection, and the first-order beam is diffracted at an angle of -47.3 degrees to the normal.

[0190] Thus, the 0th and 1st order beams make up the secondary excitation beams 402, 404.

[0191] A maximum distance is then defined between the beam splitter 40 and the focusing optical system 50. For example, consider a case where an optical fiber with a numerical aperture of 0.22 is connected to the laser source 30, and where the source light beam 302 is collimated at the output of the optical fiber by a collimating optical system 32 with a focal length of 4.5 millimeters. In this case, the laser beam 302 has a diameter of 2 millimeters once collimated. Therefore, the maximum distance between the beam splitter 40 and the focusing optical system 50 is calculated to be equal to:

[0192] d max = est equal to the maximum distance, O 50 corresponds to the diameter of the focusing optical system 50, here more particularly to the diameter of a pupil of the microscope objective described in this embodiment, O 302corresponds to the diameter of the source light beam 302, and where a corresponds to the separation angle between the secondary excitation beams 402, 404.

[0193] Here, the maximum distance between the beam splitter 40 and the focusing optical system 50 is equal to 121 millimeters given the parameters mentioned above.

[0194] Similarly, changing the focal length of the collimating optical system 32 also changes the diameter of the source light beam 302 and therefore the maximum suitable distance between the focusing optical system 50 and the beam splitter 40. Specifically, if in a variant of the embodiment described above the collimating optical system 32 has a focal length of 11 millimeters, then the diameter of the source light beam 302 is 5 millimeters. This results in a maximum distance of 85 millimeters.

[0195] In the event that the distance between the beam splitter 40 and the focusing optical system 50 exceeds the maximum distance, the secondary excitation beams may partially or totally exit the diameter of the focusing optical system 50. The performance of the light-matter interaction necessary for the study of a sample 2 by the device is thereby degraded.

[0196] Thus, in the case where the distance between the beam splitter 40 and the focusing optical system 50 exceeds the maximum recommended distance, for example, due to constraints related to the size of the backscatter laser spectrometry device 1 and / or a focusing system diameter 50 that is too small, it may be recommended to insert an afocal optical system within the device.

[0197] This afocal optical system is located in the excitation path, specifically at beam splitter 40, which is a reflection diffraction grating. The afocal optical system is implemented using two lenses: one with a specific focal length and the other with a different focal length. The spacing between the two lenses of the afocal optical system is equal to the sum of the first and second focal lengths. In this way, a light beam that is collimated upon impact with the afocal optical system emerges from it still collimated.

[0198] In this variant of the embodiment, where the beam splitter 40 includes a diffraction grating, the beam splitter 40 is inserted between the first and second lenses of the afocal optical system. Such a configuration reduces the angular divergence between the secondary excitation beams 402 and 404, so that they can be collected by the focusing optical system 50. For example, the second lens of the afocal optical system is arranged so as to image the beam splitter 40, i.e., the diffraction grating, at the center of the diameter of the focusing optical system 50. More precisely, this diameter of the focusing optical system 50 corresponds here to that of an entrance pupil of this focusing optical system 50.

[0199] The separation angle between the secondary excitation beams 402 and 404 at the output of the afocal optical system depends on the properties of the diffraction grating, as well as on the magnification of the afocal optical system. These parameters thus allow adjustment of the separation angle between the secondary excitation beams 402 and 404.

[0200] The various configuration examples described above are provided for explanatory purposes, to highlight considerations necessary for the design of a device where the beam splitter 40 is a diffraction grating. In particular, the interdependence of the different parameters described has been emphasized.

[0201] The propagation of the first secondary excitatory light beam 402 and the second secondary excitatory light beam 404 to sample 2, and the backpropagation of the first backscattered light beam 412 and the second backscattered light beam 414 along respectively the first optical path and the second optical path are identical to what has been described previously for the first and second embodiments. Variations on the methods of implementation

[0202] Figure 5 shows a variant of the first embodiment. This variant is nevertheless compatible with the other embodiments described previously. Thus, although the beam splitter 40 shown in Figure 5 is a Rochon prism, it can alternatively be a Wollaston prism, an optical fiber coupler, or a diffraction grating.

[0203] Advantageously, the beam splitter 40 is suitable for creating a relatively large separation angle between the secondary excitation beams 402, 404, in particular an angle greater than 2 degrees. More specifically, in the case of a beam splitter 40 in the form of a prism, a separation angle of 10 degrees is advantageous. Indeed, according to this variant, the focusing optical system 50 comprises a plurality of distinct optical subsystems 52, 54.

[0204] Thus, a sufficiently large separation angle between the secondary excitation beams 402 makes it possible to guarantee the collection of each of these beams by a single subsystem 52, 54 of the focusing optical system 50.

[0205] For example, a focusing optic, such as a lens, is placed on each of the spatially distinct optical paths along which the first, respectively second, secondary excitation light beams 402, 404 propagate, thus that the first, respectively second, backscattered light beam associated 412, 414.

[0206] According to a variant of the third embodiment described, where the beam splitter 40 includes a diffraction grating, an angular deviation of 4.6 degrees is suggested, for example, in order to obtain a separation of 16 millimeters between the secondary excitation beams 402, 404, after a trajectory of 200 millimeters between the beam splitter 40 and the optical subsystems 52, 54.

[0207] In general, it is recommended to choose a separation angle and / or a distance between the beam splitter 40 and the focusing optical system 50 suitable so that the beams are separated by at least the diameter of the optical subsystems 52, 54.

[0208] Each of the optical subsystems 52, 54 focuses the secondary excitation light beams 402, 404 onto measurement points 202, 204, onto distinct samples 2, 22. Here, in the case of a beam splitter 40 dividing the source light beam 302 in two, two distinct samples 2, 22 are analyzed simultaneously, in parallel with each other. These two samples 2, 22 may be of different physicochemical nature, and / or be placed in different containers and / or sample holders 20.

[0209] In particular, in accordance with the description made in this disclosure, one of the samples 22 may correspond to a calibration reference while the other sample 2 then corresponds to a sample of interest in the context of the measurement and / or analysis.

[0210] In order to adapt to two containers and / or sample holders, such as, for example, windows of different thicknesses, the two separate optical subsystems 52, 54 of the optical focusing system 50 can each have adapted focal lengths, longer or shorter depending on the distance to the sample 2, respectively 22.

[0211] In the variant shown in Figure 5, the focusing optical system 52 positioned on the first optical path has a focal length of of 18 millimeters for example, identical to the optical focusing system 54 positioned on the second optical path has a focal length of of 18 millimeters as well. However, two optical focusing systems 52, 54 of different focal lengths, identical or not, are also possible within the framework of this disclosure.

[0212] Furthermore, it is also possible to offset the axial position of a focusing optical system 52 relative to the axial position of a focusing system 54. In this case, the two optical systems 52 and 54 may have identical focal lengths. Second variant

[0213] According to another variant of the first embodiment, shown in Figure 6, a second separating element 62 is inserted between the first separating element 60 and the focusing optical system 50. This second separating element 62 is placed on both the first optical path and the second optical path.

[0214] This second separating element 62 preferentially uses polarization to separate the light beams. It should be noted that this variant is only compatible with embodiments where the secondary excitation light beams 402 and 404 are described by different polarization states. In particular, the two polarization states are orthogonal. As a reminder, the first secondary excitation light beam 402 has vertical polarization, while the second secondary excitation light beam 404 has horizontal polarization.

[0215] The second beam splitter element 62 corresponds to a polarized plate beamsplitter, oriented at an angle close to 45 degrees to the first and second optical paths. It can also be a polarized cube beamsplitter, positioned so as to be close to an angle of incidence normal to the first and second optical paths.

[0216] Depending on the direction of incident polarization, the second separator element 62 is adapted to reflect one beam and transmit the orthogonally polarized beam.

[0217] In the first embodiment described, where the beam splitter 40 is a birefringent prism, the first secondary exciter light beam 402 and the second exciter light beam 404 are linearly polarized in directions orthogonal to each other.

[0218] By orienting the second beam splitter 62 appropriately with respect to the polarization directions of the incident beams, the second beam splitter 62 transmits, for example, the first secondary excitation light beam 402 and reflects the second excitation light beam 404. The first secondary light beam 402 is therefore oriented in a direction close to perpendicular with respect to the second secondary excitation light beam 404. The same applies to the first optical path and the second optical path.

[0219] Similar to the variant described previously, the focusing optical system 50 consists of two subassemblies 52, 54, each placed on one of the optical paths. Each of the subassemblies 52, 54 focuses the incident beam onto a measurement point 202, 204 on the samples 2, 22, before collecting the light backscattered light from measurement point 202 and measurement point 204. The first backscattered light beam 412 has a priori a vertical polarization, and the second backscattered light beam 414 has a priori a horizontal polarization.

[0220] The second beam splitter 62, i.e., the polarized beam splitter plate, is therefore adapted to transmit the first backscattered light beam 412 and to reflect the second backscattered light beam 414. These backscattered light beams 412, 414 are therefore counter-propagating with respect to the secondary excitation light beams 402, 404, up to the beam splitter 60. The rest of the collection path remains identical to the descriptions given previously.

[0221] Alternatively, the second beam splitter 62 corresponds to a beam splitter plate, i.e., a non-polarized beam splitter plate. In this case, this variant becomes compatible with embodiments where the beam splitter 40 corresponds, for example, to a prism, such as a Rochon or Wollaston prism, or an optical fiber coupler, or even a diffraction grating.

[0222] Such a beam splitter blade is suitable for reflecting part of the incident light and transmitting the other part.

[0223] Alternatively, the second beam splitter 62 corresponds to a D-shaped mirror, that is, a semi-circular mirror. Such a second beam splitter 62 is then arranged within the backscattering laser spectrometry device 1 so as to reflect only one of the secondary excitation light beams 402, 404. For example, the second beam splitter 62 is arranged to reflect the second secondary excitation light beam 402, while allowing the first secondary excitation light beam 404 to pass through.

[0224] Regardless of the means adopted for the second separating element 62, this proposed variant allows the two secondary excitation light beams 402, 404 to be offset by 90 degrees from each other, in order to simultaneously study two distinct samples 2, 22 using two subsystems 52, 54 of the focusing optical system 50. Process

[0225] The invention also relates to a laser backscatter spectrometry method using the laser backscatter spectrometry device 1 as described above for measuring and / or analyzing a sample 2 of interest. In this laser backscatter spectrometry method, a measurement and / or analysis of this sample 2 is carried out simultaneously at a first measurement point 202 and a second measurement point 204, under similar experimental conditions.

[0226] This process comprises several steps, including, firstly, the division, by a beam splitter 40 placed in the optical path of a source light beam 302 emitted by a laser source 30, of this source light beam 302 into a plurality of beams, in particular a first, respectively a second, secondary exciter light beam 402, 404. This first, respectively second, secondary exciter light beam 402, 404 propagates along two optical paths, i.e. a first optical path and a second optical path.

[0227] The second step consists of the simultaneous direction of the first secondary exciter light beam 402 and the second secondary exciter light beam 404 towards the focusing optical system 50. This step is carried out by the insertion on the first optical path and the second optical path of an optical separator 60 as described previously.

[0228] In the third step, the focusing of the first, respectively second excitation light beams 402, 404 in a plane of the sample is achieved by an optical focusing system 50. A measurement point 202, 204 is thus generated for each of the secondary excitation light beams 402, 404. These measurement points 202, 202 are spatially distinct from each other on the sample 2.

[0229] The fourth step is the collection by the focusing optical system 50 of the backscattered beams 412, 414 associated with each of the measurement points 202, 204, in particular of the first backscattered light beam 402, and of the second backscattered light beam 404. These backscattered light beams 412, 414 propagate along the first, respectively the second, optical path, to the optical separator 60.

[0230] In a fifth step, the separation operated by the optical separator 60 makes it possible to distinguish the backscattered beams 412, 414 containing a light signal from sample 2, and the secondary excitation light beams 402, 404, which were used for the generation of the light-matter interaction.

[0231] In the sixth step of the process, an optical injection system 70 directs the first, and second, backscattered light beams 412 and 414 onto an inlet 82 of the spectrometer 80. The first inlet point 822 of the first backscattered light beam 412 is at a height H1 of the inlet 82, while the second inlet point 824 is located at a height H2 of the inlet 82. These heights H1 and H2 are different and sufficiently separated from each other to maintain the separation of the light signals from each of the measurement points 202 and 204.

[0232] During the seventh step, the spectrometer 80 performs the spectral dispersion of the first, respectively second, backscattered light beam 412, 414 on a first, respectively second zone 842, 844 of a multichannel detector 84. Indeed, as a reminder, the spectrometry signal 902, 904 considered here is a spectrum, such as a Raman spectrum, or a photoluminescence spectrum, or a fluorescence spectrum.

[0233] Finally, the backscatter laser spectrometry process includes a step of simultaneous reading by a processing unit 90 of a first, respectively second spectrometry signal 902, 904, acquired on the first, respectively second, zone 842, 844 of the multichannel detector 84. The first, respectively second spectrometry signal 902, 904 is representative of the first, respectively second measurement point 202, 204 of the sample 2. Variants

[0234] The present invention is in no way limited to the embodiments described and represented, but a person skilled in the art will be able to make any variation in accordance with the invention.

Claims

DEMANDS 1. A backscatter laser spectrometry device (1) comprising a laser source (30) emitting a source light beam (302), an optical focusing system (50), an optical splitter (60), a spectrometer (80) comprising an input (82) and a multichannel detector (84), and a processing unit (90), characterized in that the laser spectrometry device (1) comprises: - a beam splitter (40) disposed on an optical path of the source light beam upstream of the optical separator (60), the beam splitter (40) being adapted to divide the source light beam (302) into a first secondary excitation light beam (402) propagating along a first optical path and a second secondary excitation light beam (404) propagating along a second optical path, - the optical separator (60) being disposed on the first optical path and on the second optical path, the optical separator (60) being adapted to simultaneously direct the first secondary excitation light beam (402) and the second secondary excitation light beam (404) towards the focusing optical system (50), - the optical focusing system (50) being arranged and configured to focus the first, respectively second, secondary excitation light beam (402, 404) on a first, respectively second, measurement point (202, 204), the first measurement point (202) being spatially separated from the second measurement point (204), - said focusing optical system (50) being adapted to collect a first, respectively second, backscattered light beam (412, 414) emitted by the first, respectively second measurement point (202, 204), propagating in the opposite direction to the first, respectively second, secondary excitation light beam (402, 404) following the first, respectively second, optical path to the optical separator (60), - the optical splitter (60) and an optical injection system (70) being adapted to direct the first, respectively second, backscattered light beam (412, 414), towards a first, respectively second, point (822, 824) of the inlet (82) of the spectrometer (80), the first point (822) of the inlet (82) of the spectrometer being spatially separated from the second point (824) of the inlet (82) of the spectrometer (80), - said spectrometer (80) being adapted to direct the first, respectively second, backscattered light beam (412, 414) onto a first, respectively second, zone (842, 844) of the multichannel detector (84), the unit of treatment (90) being adapted to deduce a first spectrometry signal (902) acquired on the first zone (842) and a second spectrometry signal (904) acquired on the second zone (844).

2. Laser backscatter spectrometry device (1) according to claim 1, wherein said beam splitter (40) is a prism.

3. Laser backscatter spectrometry device (1) according to claim 1, wherein said beam splitter (40) is a fiber coupler comprising an inlet adapted for injecting the source light beam (302), a first fiber output branch adapted for propagating the first secondary excitation light beam (402) and a second fiber output branch adapted for propagating the second secondary excitation light beam (404).

4. Laser backscatter spectrometry device (1) according to claim 1, wherein said beam splitter (40) comprises a diffraction grating.

5. Laser backscatter spectrometry device (1) according to any one of claims 1 to 4, wherein the focusing optical system (50) comprises a first focusing optical system (52) placed on the first optical path traversed by the first secondary excitation light beam (402) and a second focusing optical system (54) placed on the second optical path traversed by the second secondary excitation light beam (402), the first focusing optical system (52) and the second focusing optical system (54) having different optical properties.

6. Laser backscatter spectrometry device (1) according to claim 5, wherein the first focusing optical system (52) and the second focusing optical system (54) have focal lengths of different values.

7. Backscatter laser spectrometry device (1) according to any one of claims 1 to 6, wherein the first secondary excitation light beam (402) and the second secondary excitation light beam (404) have polarization states distinct from each other.

8. Backscatter laser spectrometry device (1) according to any one of claims 1 to 7, comprising a reference sample on which the second measurement point (204) is located and in which said second backscattered beam (414) serves as a calibration reference for the first backscattered beam (412).

9. A laser backscatter spectrometry method, wherein an analysis of at least one sample (2) is carried out simultaneously at a first measurement point (202) and a second measurement point (204), said laser backscatter spectrometry method is characterized in that it comprises the following steps: - division by a beam splitter (40) arranged on an optical path of a source light beam (302), into a first secondary excitation light beam (402) following a first optical path and a second secondary excitation light beam (404) following a second optical path, - simultaneous direction of the first secondary excitation light beam (402) and the second secondary excitation light beam (404) towards a focusing optical system (50) via an optical splitter (60) disposed on the first optical path and the second optical path, - focusing by the optical focusing system (50) of the first, respectively second, secondary excitation light beam (402, 404) on a first, respectively second measurement point (202, 204), the first measurement point (202) being spatially separated from the second measurement point (204), - collection by the focusing optical system (50), of a first, respectively second, backscattered light beams (412, 414) emitted by the first, respectively second, measurement point (202, 204), propagating in the opposite direction of the first, respectively second, secondary excitation light beam (402, 404), following the first, respectively second, optical path to the optical separator (60), - separation by the optical separator (60) of the first, respectively second, backscattered light beam (412, 414) from the first, respectively second, measurement point (202, 204), and of the first, respectively second secondary excitation light beam (402, 404), - direction by the optical splitter (60) and by an optical injection system (70) of the first, respectively second, backscattered light beam (412, 414), towards a first, respectively second point (822, 824) of an inlet (82) of a spectrometer (80), said first, respectively second point (822, 824) being spatially separated from each other, - direction by the spectrometer (80) of the first, respectively second, backscattered light beam (412, 414) on a first, respectively second zone (842, 842) of a multichannel detector (84), - simultaneous reading by a processing unit (90) of a first, respectively second, spectrometry signal (902, 904) acquired on the first, respectively second zone (842, 844), and representative of the first measurement point (202) and the second measurement point (204) of the sample (2).

10. A laser backscatter spectrometry method according to claim 9, wherein said spectrometry signal (902, 904) is a Raman spectrum or a fluorescence spectrum or a photoluminescence spectrum.

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