EP3794325A1 - Composite multispectral raman spectroscopy method and device - Google Patents

Abstract

The invention relates to a Raman spectroscopy device (1) comprising a source system (2) generating a first excitation light beam at a first excitation frequency, a spectral separation system (8), a system for detection (10) in an observation spectral range, and a computer (12) generating a first part of the Raman scattering spectrum in a first Raman spectral range extending between a first relative wave number and a second relative wave number. According to the invention, the source system is adapted to generate a second excitation light beam at a second excitation frequency different from the first excitation frequency, the computer generating a second part of the Raman scattering spectrum in a second Raman spectral range, expressed as wave number as a function of the same observation spectral range, said second spectral range extending between a third relative wave number and a fourth relative wave number. The invention also relates to a Raman spectroscopy method.

Description

 APPARATUS AND METHOD FOR COMPOSITE RAMAN MULTISPECTRAL SPECTROMETRY

TECHNICAL FIELD TO WHICH THE INVENTION REFERS

The present invention generally relates to the field of Raman spectrometry.

 It relates more particularly to an apparatus and a method of Raman spectrometry.

 BACKGROUND

 The observation of spectral domains towards high wavenumbers by Raman spectrometry (referred to as high frequency Raman spectrometry) generally requires adjustments involving the displacement of optical components or the use of other optical components, or following the case, more suitable detection systems increasing the complexity and therefore the cost of the device. These conventional systems of Raman spectrometry are generally limited in spectral resolution and / or in the observed spectral domains.

From the known devices, it is possible to obtain a good spectral resolution by restricting the spectral range. The use of a spectrometer with a mobile dispersive system then makes it possible to successively probe the entire spectral domain. In general, this configuration induces a decrease in detectivity of the detection system at very high wavenumbers (greater than 4000 cm ¹ ).

 Another known configuration consists of choosing a fixed spectral separation system for the entire spectral domain but with a lower spectral resolution.

 Yet another configuration is to use a mask comprising a set of slots in front of the detection system to refine the resolution, and successively shift this mask to solve the spectrum over the entire spectral range.

 This technology applies to a Raman spectrometry apparatus, for which it is desirable to extend the spectral range and / or increase the spectral resolution, while maintaining the compactness, simplicity and therefore its cost and strength but also its reproducibility.

 OBJECT OF THE INVENTION

In order to overcome the aforementioned drawbacks of the state of the art, the The present invention provides a Raman spectrometry apparatus.

 More particularly, it is proposed according to the invention a Raman spectrometry apparatus for characterizing a sample, the apparatus comprising a source system generating a first incident light beam excitation at a first excitation wavelength, a system of spectral separation receiving a first scattered light beam formed by scattering said first incident excitation light beam onto the sample and spectrally separating said first scattered light beam, a detection system for recording a first Raman signal associated with said first scattered light beam and detected in a spectral wavelength observation range extending between a first observation wavelength and a second observation wavelength, a computer receiving the first Raman signal of said detection system and generating a first part of Raman spectrum in function Raman displacement in a first Raman spectral domain in relative wavenumber, said first Raman spectral domain extending between a first relative wavenumber function of the first excitation wavelength and the first wavelength observation wave and a second relative wave number according to the first excitation wavelength and the second observation wavelength.

According to the invention, said source system is adapted to generate at least a second excitation incident light beam at a second excitation wavelength, said second excitation wavelength being different from the first excitation wavelength. excitation wave, said spectral separation system being adapted to receive a second scattered light beam formed by scattering said incident incident light beam onto the sample and spectrally separating said second scattered light beam, said detection system being adapted to detect and record a second Raman signal associated with said second light beam scattered in the same wavelength observation spectral range, said computer being adapted to measure the second Raman signal and to generate a second portion of Raman spectrum according to of Raman displacement in a second Raman spectral domain in name relative wavelength, said second Raman spectral domain extending between a third relative wavenumber according to the second wavelength of excitation and the first wavelength of observation and a fourth relative wave number according to the second excitation wavelength and the second observation wavelength, the second Raman spectral domain being different from the first Raman spectral domain in number of a relative wave, the first part of the Raman spectrum and the second part of the Raman spectrum being intended to be combined to reconstitute a Raman scattering spectrum over an extended spectral range in relative wavenumber and / or having an increased spectral resolution in the first and / or second Raman spectral domain.

 Advantageously, in the configuration of the invention, different excitation wavelengths are used in combination without modifying the detection filter or filters. A relatively narrow spectral observation interval then makes it possible to obtain as many different portions of the Raman spectrum on different spectral domains in relative wavelengths as excitation wavelengths, then allowing the constitution of a set of parts. Raman spectra or the reconstitution of an extended Raman spectrum and / or increased spectral resolution in relative wavenumber. The compactness of the spectrometry apparatus and its simplified use are then improved because only the excitation wavelengths are modified, no further adjustment is necessary.

 Other non-limiting and advantageous features of the Raman spectrometry apparatus according to the invention, taken individually or in any technically possible combination, are as follows:

 the source system is adapted to generate a plurality of excitation light beams at a plurality of excitation wavelengths;

 the source system comprises a plurality of monochromatic laser sources, an optical frequency tunable laser source and / or a source generating a plurality of spatially selectable or spatially separable monochromatic excitation wavelengths;

 the source system comprises a continuous or pulsed laser source;

at least one device for polarizing the excitation light beam between the source system and the sample is provided, said polarization device being adapted to polarize the first excitation incident light beam according to at least two polarization states; different, for example orthogonal to each other, and respectively the second excitation incident light beam according to at least two different polarization states, for example orthogonal to each other;

 - There is also provided a polarization analyzer disposed between the sample and the detection system, the polarization analyzer being adapted to analyze and / or polarize the first scattered light beam and, respectively, the second scattered light beam;

 the computer is configured to retain the first part of the Raman scattering spectrum and the second part of the Raman scattering spectrum and to constitute a set of parts of Raman spectra or to combine the first part of the Raman spectrum and the second part of the Raman spectrum; reconstructing an extended Raman spectrum and / or increased spectral resolution in relative wavenumber;

 the computer is adapted to generate a first, respectively second, part of the hyper Raman scattering spectrum in a first, respectively second, hyper Raman displacement spectral domain in relative wave number, in which the first relative wave number is equal to the difference between a product of an integer n and the first excitation wave number and the first observation wave number, the second relative wave number is equal to the difference between a product of the integer n and the first excitation wave number and the second observation wave number, the third relative wave number is equal to the difference between a product of the integer n and the second wavenumber excitation number and the first observation wave number, the fourth relative wave number is equal to the difference between a product of the integer n and the second excitation wave number and the second x number of observation wave, the integer multiple n being greater than or equal to two;

 - There is also provided a detection filter configured to cut the first excitation wavelength and / or the second excitation wavelength;

 the filter in detection comprises at least one high-pass filter, a low-pass filter or a band-pass filter or a combination of said filters;

the spectral separation system comprises a spectrometer based on diffraction grating (s), prism (s) and / or grism (s) or a spectrometer comprising a combination of diffraction grating (s) and / or prism (s) and / or grism (s);

 the spectral separation system comprises an interference filter and / or an interferometer;

 the filter in detection is fixed; and

 the detection system comprises a single-channel detector or a one-dimensional linear detector or a two-dimensional matrix detector.

 The invention also proposes a Raman spectrometry method comprising the following steps:

 generating a first excitation incident light beam at a first excitation wavelength by a source system;

 spectral separation of a first scattered light beam formed by diffusion of the first incident light beam excitation on a sample;

 recording of a first Raman signal associated with the first scattered light beam, detected in a spectral wavelength observation range extending between a first observation wavelength and a second wavelength of observation;

 calculating a first portion of Raman spectrum as a function of the Raman displacement in a first Raman spectral domain in relative wave number, said first Raman spectral domain extending between a first relative wave number and a function of the first length of the Raman spectrum. excitation wave and the first observation wavelength and a second relative wave number according to the first excitation wavelength and the second observation wavelength;

 generating at least one second excitation incident light beam at a second excitation wavelength by the source system, said second excitation wavelength being different from the first wavelength of excitation; excitement;

 spectral separation of a second scattered light beam formed by diffusion of the incident incident light beam onto the sample;

 recording a second Raman signal associated with the second scattered light beam, detected in the same wavelength observation spectral range;

calculation of a second part of the Raman spectrum according to the Raman shift in a second Raman spectral domain in relative wavenumber, said second Raman spectral domain extending between a third relative wavenumber function of the second excitation wavelength and the first wavelength of observation and a fourth relative wave number according to the second excitation wavelength and the second observation wavelength, the second Raman spectral domain being different from the first Raman spectral domain in number of relative wave; and

 combining said first portion of the Raman scattering spectrum and said second portion of the Raman scattering spectrum to reconstitute a Raman scattering spectrum over an extended spectral range in relative wavenumber and / or having an increased spectral resolution in the first and / or second Raman spectral domain.

 DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

The following description with reference to the accompanying drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be achieved.

 In the accompanying drawings:

 - Figure 1 provides a schematic representation of the various elements of a Raman spectrometry apparatus according to the invention;

 FIG. 2 provides an example of an instrumental configuration of the Raman spectrometry apparatus according to the invention;

 FIG. 3 proposes a schematic representation of the spectral domains obtained in relative wavenumber for several proposed excitation wavelengths;

 FIG. 4 represents an example of several portions of Raman scattering spectra in Stokes configuration, acquired at several excitation wavelengths and represented as a function of the observation wavelength;

 FIG. 5 represents an example of Raman scattering spectrum portions in Stokes configuration calculated from the spectral portions of FIG. 4 and represented as a function of the Raman displacement expressed in relative wavenumber;

FIG. 6 represents an example of several parts of Raman scattering spectra in anti-Stokes configuration, acquired at several excitation wavelengths and represented as a function of the wavelength. observation;

 FIG. 7 represents the examples of Raman scattering spectrum parts in anti-Stokes configuration calculated from the spectral portions of FIG. 6 acquired at different excitation wavelengths, and represented as a function of the Raman displacement expressed in FIG. relative wave number;

 FIG. 8 represents an example of hyper Raman scattering spectrum parts in Stokes configuration, acquired at different excitation wavelengths and represented as a function of the observation wavelength;

 FIG. 9 represents the examples of Stokes hyper-Raman scattering spectrum parts calculated from the spectral portions of FIG. 8 and represented as a function of the Raman displacement expressed as a relative wavenumber;

 FIG. 10 proposes another schematic representation of the different elements of a Raman spectrometry apparatus according to the invention;

 FIG. 11 represents an example of several parts of Raman scattering spectra acquired at several excitation wavelengths and represented as a function of the wavelength of observation;

 FIG. 12 represents an example of Raman scattering spectrum parts calculated from the spectral portions of FIG. 11 and represented as a function of the Raman displacement expressed in relative wavenumber;

 FIG. 13 proposes a schematic representation of the spectral domains obtained in relative wavenumber for several proposed excitation wavelengths and several spectral separation systems, the x-axis being in wavelength; and

 FIG. 14 proposes a schematic representation of the spectral domains obtained in relative wave number of FIG. 13 for several proposed excitation wavelengths and several spectral separation systems, the x-axis being in wave number relative.

Throughout this description, the terms wavelength and wavenumber will be used, the relationship between the two terms being described by the following formula (1):

where v is the wavenumber, expressed in cm ¹ and l is the wavelength expressed in nm.

The Raman effect consists of the inelastic scattering of photons by a material, a solution or a gas. Throughout this description, the Raman shift or Raman shift is always expressed as a difference in wave numbers, here noted Nv _Raman . The Raman displacement is equal to the difference between a wave number corresponding to the wavelength of the excitation incident light beam and a wavenumber corresponding to a wavelength in a spectral observation interval. The Raman displacement in wavenumber, referred to herein as the relative wave number, of the excitation with respect to the observation, is given by the following formula:

wherein the difference or difference in wave numbers Dn _Ka7hah expressed in relative wavenumber (in cm ¹ ), corresponds to the Raman shift or Raman shift, _{Δt exc} corresponds to the excitation wavelength and λ _obs corresponds to a wavelength in the spectral observation interval, at and at _{exc obs} being expressed in nm. The negative values of Dn _Ka7hah correspond to the anti-Stokes Raman scattering and the positive values of αv _Raman correspond to the Raman Stokes scattering.

In the case of the n-photon hyper Raman configuration, the relative wave number is thus formed by the difference between an integer multiple of the excitation wave number and the observation wave number: Av _Ram an = ⁿ - v _e xc ^~ v ₀ bs (3), with n ³ 2.

 A Raman shift or Raman shift spectral domain, hereinafter referred to as the Raman spectral domain, is defined as a relative wavenumber.

 Device and method

 Figure 1 provides a schematic representation of the elements of a Raman spectrometer apparatus 1 according to the invention.

The Raman spectrometry apparatus 1 comprises a source system 2, an optional polarization device 4, an optional optical system 3 for guiding and / or focusing and / or collimation and / or beam shaping, a spectral separation system 8, a detection filter 9, a detection system 10 and a computer 12. The Raman spectrometry apparatus 1 is intended to to characterize a sample 6.

The source system 2 is adapted to generate an incident excitation light beam at at least a first excitation wavelength, denoted by _exCi and at a second excitation wavelength _exC2 . In an exemplary embodiment, the source system 2 comprises a plurality of monochromatic laser sources 21, 22. The first laser source 21 generates an excitation light beam at the first excitation wavelength _{λ exCl} ,

corresponding to a first excitation wave number v _exc = -. The second exc-i

laser source 22 generates an excitation light beam at the second excitation wavelength corresponding to a second excitation wave number v _exc = -. In this case, a plurality of laser sources exc2

In one embodiment, the source system 2 comprises a wavelength tunable laser source. According to another alternative, the source system 2 comprises a plurality of wavelength tunable sources. According to another alternative, the source system 2 comprises a selected multi-wavelength source. The source system 2 generates an incident light beam of continuous or pulsed excitation.

 Optionally, the Raman spectrometry apparatus 1 comprises a polarization device 4. The polarization device 4 can be integrated in the source system 2 or separated from the source system 2. This polarization device 4 is described below, in connection with FIG. with the application to the Raman Optical Activity Measurement (ROA).

Advantageously, the Raman spectrometry apparatus 1 comprises an optical system 3 for guiding and / or collimating and / or focusing and / or shaping the beam. The optical system 3 may be integrated at least in part with the source system 2 or separated from the source system 2. The incident light excitation beam is directed towards the optical system 3 for guiding and / or collimating and / or focusing and / or shaping the beam. The optical system 3 is configured to direct and adapt the light beam to the sample 6. In practice, the optical system 3 may comprise a set of lenses and / or mirrors and / or an optical fiber and / or a set of optical fibers. Preferably, the optical fiber used is a hollow fiber which makes it possible to limit the parasitic signals during the transmission of the light beam. The optical system 3 may comprise a confocal optical device with a mirror and / or a microscope objective.

 The incident light beam excitation at the first excitation wavelength is diffused by the sample 6 and generates a first scattered light beam. Throughout this description, the name "light beam scattered by the sample" will also take into account the case of scattered light beams regardless of the direction of observation, particularly the example of light beams backscattered by opaque samples by example. Similarly, the incident light beam excitation at the second excitation wavelength is scattered by the sample and generates a second scattered light beam.

 A collection optical system 7 can make it possible to collect the light beam scattered by the sample 6. In the case of backscattered light beams, the collection optical system 7 can be confused with the optical system 3 for guiding and / or collimating and / or focusing and shaping the beam.

 The Raman spectrometry apparatus 1 comprises a spectral separation system 8 adapted to receive and spectrally separate the light beam scattered by the sample 6. In an exemplary embodiment, the spectral separation system 8 comprises a network-based spectrometer ( x) diffraction (or "diffraction grating" according to the English terminology) or a spectrometer based prism (s) or a spectrometer based on grism (s) or a spectrometer comprising a combination of network (s) of (x) diffraction and / or prism (s) and / or grism (s). The light beam scattered by the sample 6 is thus dispersed spatially at its different wavelengths.

In another exemplary embodiment, the spectral separation system 8 can also comprise one or more band-pass or interference filters and / or an acousto-optical adjustable filter (or AOTF for "Acousto-Optic Tunable Filters" according to the English terminology). Saxon) and / or an interferometer generally limited in spectral domain. In the case of a interferometer, the different wavelengths of the scattered light beam are separated by interferometry.

The Raman spectrometry apparatus 1 also comprises at least one detection filter 9 disposed between the sample and the spectral separation system 8 in the path of the first, respectively, second scattered light beam. The filter 9 is generally placed after the collection optical system 7. This filter 9 intersects the first excitation wavelength _{λ exCi} and the second excitation wavelength _exC2 , thus suppressing the Rayleigh scattering of said scattered light beams. . This filter 9 passes all the wavelengths of the spectral observation interval. The use of the filter 9 differs from known prior art devices in which is preferably used a notch filter (or "notch filter" according to the English terminology used), narrowband filter (of the order of few nanometers) centered on a determined excitation wavelength in order to eliminate it from the collected signal.

In an exemplary embodiment, the filter 9 may be a high-pass filter for observing Raman Stokes scattering. In this case, the filter has a cut-off wavelength located strictly between the highest excitation wavelength, for example _{λ exCl} , and the lowest observation wavelength _λ . In another embodiment, the filter 9 may be a low-pass filter for the observation of anti-Stokes Raman scattering. In yet another example, the filter 9 may be a bandpass filter for the simultaneous observation of Raman Stokes and anti-Stokes scatterings. In the case of simultaneous observation of Raman Stokes and anti-Stokes scatterings, an additional jet-type filter centered on the excitation wavelength is used to filter the excitation wavelength in question. . Such a rejection filter only makes it possible to block the excitation wavelength in the spectral observation interval. For excitation wavelengths outside the spectral observation range, all the wavelengths outside the observation spectral range are cut off. A rejection filter can also be used only to limit the brightness at the detection system.

The first, respectively second, spectrally separated light beam is directed to the detection system 10. Preferably, the spectral range of observation of the detection system 10 is set. This spectral range of observation extends between a first observation wavelength at _obSi and a second observation wavelength at _obS2 . For example, the spectral range of observation may range between _λ = 790 nm and _obs2 = 920 nm. Prior art devices of Raman spectrometry using a fixed spectral separation system are generally configured to acquire measurements over the widest spectrum possible in wavelength. According to the configuration of the invention, the width of the spectral observation range is relatively narrow, for example here 130 nm.

 In an exemplary embodiment with a diffraction grating-based spectrometer, the detection system 10 comprises a one-dimensional linear detector or a two-dimensional matrix detector, for example a CCD or CMOS-type camera for visible detection. and near-infrared or InGaAs or MCT for infrared detection.

 In yet another embodiment, the spectral separation system 8 comprises an interference filter, possibly combined with a bandpass filter. In this case, the detection system 10 then comprises a detector allowing a temporal tracking of the interference signal on this detector. By temporal tracking of the signal is meant an interference system in which a mirror is moved as a function of time to observe the interference fringes. The Raman spectrum in relative wavenumber is reconstructed by Fourier transform from the interferogram.

 The detection system 10 generally comprises a detector that makes it possible to convert the photons that it receives from the scattered beam into electrons and to accumulate these electrons. The detection system 10 usually includes an analog-to-digital converter adapted to count the accumulated electrons and convert these measurements into numerical values. The detection system 10 thus records in the form of numerical values a first, respectively second, Raman scattered signal, hereinafter called Raman signal, associated with the first, respectively second, scattered light beam and separated spectrally by the spectral separation system 8 in the selected spectral range of observation.

A calculator 12 is adapted to receive the first, respectively second, registered Raman signal as numerical values. In generally, the computer 12 is adapted to generate a first, respectively second, spectrum of the Raman signal, also called Raman spectrum part in the following, depending on the excitation wavelength and the selected spectral range of observation wavelength [A _ofcSl A _ofcs J.

The computer 12 is adapted to calculate a first, respectively second, part of the Raman scattering spectrum as a function of the relative wave number calculated with respect to the first excitation wave number v _exCi , respectively to the second wave number. of excitation v _exC2 , associated with the incident light beam of excitation. This first, respectively second, part of the Raman spectrum is calculated in a first, respectively second, Raman spectral domain, expressed as a relative wavenumber depending on the excitation wavenumber and the observation spectral interval, expressed wavenumber _[OBS2 v, v J _obs. For the first _exCl excitation _wavelength , the first Raman spectral domain extends between a first relative wave number corresponding to the difference between the first excitation wave number v _exCi and the number of maximal observation wave v _obSi and a second relative wave number Dn ₂ corresponding to the difference between the first excitation wave number v _exCi and the minimum observation wave number v _obS2 . For the second excitation wavelength A _exCz , the second Raman spectral domain extends between a third relative wave number Dn ₃ corresponding to the difference between the second excitation wave number v _exC2 and the number maximum observation waveform v _obSi and a fourth relative wave number Dn ₄ corresponding to the difference between the second excitation wave number v _exC2 and the minimum observation wave number v _obS2 . In other words, the computer converts the first, respectively second, Raman signal expressed in wavelength into a first, respectively second, part of the Raman spectrum expressed as a relative wavenumber. The first Raman spectral domain and the second Raman spectral domain are different in relative wavenumber. The first Raman spectral domain and the second Raman spectral domain may be disjoint or partially overlapping.

Prior art devices of Raman spectrometry generally use a single excitation wavelength and adapt the system of spectral separation and / or the detection system to obtain a Raman spectrum expressed as a function of the largest possible relative wave number. On the contrary, in the configuration of the invention, different excitation wavelengths are used in combination preferably with a single detection filter or possibly in some cases with several detection filters. The detection filter or filters may remain fixed despite the change in excitation wavelength. A relatively narrow spectral observation interval then makes it possible to obtain as many different parts of the Raman spectrum on different spectral domains in relative wavenumber as excitation wavelengths, then allowing the reconstruction of an extended Raman spectrum. and / or possibly with a high spectral resolution by adapting the spectral separation system 8. The device according to the invention also makes it possible to obtain some parts of specific Raman spectra with a high spectral resolution and / or remote from each other in number relative wave.

 The Raman spectrometry apparatus 1 described above makes it possible to implement the following method of characterizing a sample by Raman spectrometry.

According to the method of the invention, the source system 2 generates a first excitation incident light beam at a first excitation wavelength _{λ exCi} which corresponds to a first excitation _wavenumber v _exCl . For example, one can choose as the first excitation wavelength = 785 nm, as the first example shown in Figure 2 (top).

The first excitation light beam is directed towards the optical system 3 for guiding and / or collimation and / or focusing and / or shaping before being diffused by the sample 6 to be characterized. A first scattered light beam, formed by diffusion of the first excitation incident light beam on the sample 6, is propagated after the sample 6 towards the detection filter 9. Advantageously, this filter 9 blocks the first length of the light. _ExCi excitation _wave , thus suppressing Rayleigh scattering.

 The first scattered light beam is then directed to the spectral separation system 8 which generates a first spectrally separated scattered light beam.

The first scattered light beam separated spectrally is analyzed by the detection system 10. The detection system 10 records a first Raman signal associated with the first scattered light beam. This first Raman signal is detected in a spectral wavelength observation interval. This spectral observation interval extends between a first observation wavelength At _obSi and a second observation wavelength _obS2 . Equivalently, the observation spectral interval can be expressed as a wavenumber, with v _obS1 the first observation _wavenumber and v _obS2 the second observation wavenumber. The filter 9 passes all the wavelengths contained in this spectral observation range and blocks the excitation wavelengths. According to a variant, a complementary filter is used in order to further filter each excitation wavelength and to avoid any parasitic signals at the level of the detection system 10. For example, in FIGS. 2 and 3, FIG. spectral range of observation defined by the spectral separation system 8 extends between 790 nm and 920 nm. In FIG. 2, the detection filter 9 is represented by a dashed line.

 In general, the computer 12 determines a first wavelength Raman spectrum from the first Raman signal in the observation spectral range, in the examples of FIGS. 2 and 3, between 790 nm and 920 nm.

The computer 12 generates a first portion of Raman spectrum expressed as a function of the relative wave number Dn _Ka7hah , itself a function of the first excitation wave number v _exCi and the spectral observation interval (on the examples Figures 2 and 3, between 790 nm and 920 nm). In other words, the computer converts the first Raman signal expressed in wavelength into a first portion of Raman spectrum expressed in relative wavenumber. The first part of Raman spectrum extends between a first relative wave number Dn- _L = ^ exc ₁ ^~ ^ obs ₁ and a second relative wave number Dn ₂ = v _exCi -v _obS2 . For example, in FIGS. 2 and 3, for a first excitation wavelength _{λ exCi} of 785 nm, for an observation spectral interval of between 790 nm and 920 nm, the first Raman spectral domain extends from = 81 cm ^-1 to Dn ₂ = 1869 cm ^_1.

The source system 2 is adapted to generate a second excitation incident light beam at a second excitation wavelength _exC2 corresponding to a second excitation wave number v _exC2 . Said second excitation wavelength is different from the first excitation wavelength at _exC2 ¹ to _exCi . For example, one can choose as the second excitation wavelength = 690 nm, as the second example shown in Figures 2 and 3 (second line from the top in Figures 2 and 3). Advantageously, the difference between the first excitation wavelength and the second excitation wavelength is between a few nm and a few hundred nm.

 As for the first excitation incident light beam, the second excitation incident light beam is directed towards the optical system 3 for guiding and / or collimation and / or focusing and shaping then to the sample 6 to be characterized. A second scattered light beam is formed by diffusion, by the sample 6, of the second excitation incident light beam.

 As for the first scattered light beam, the second scattered light beam is then filtered by the detection filter 9 and separated by the spectral separation system 8, and finally directed towards the detection system 10. This detection system 10 measures and records a second Raman signal associated with the second scattered and spectrally separated light beam. This second Raman signal is detected in the same wavelength observation spectral range, which extends for the examples of FIGS. 2 and 3 between 790 nm and 920 nm. The detection system 10 then converts the Raman signals into numerical values.

The calculator 12 then calculates a second part of the Raman spectrum associated with the second signal scattered in a second Raman spectral domain, expressed in terms of wavenumber relative to _Raman as a function of the second number. spectral observation in wavenumber. The spectral domain of this second part of the Raman spectrum extends between a third relative wave number Dn ₃ = - v _obSl and a fourth relative wave number Dn ₄ = - v _obS2 . For example, in FIGS. 2 and 3, for a second excitation wavelength _{λ exC2} of 690 nm, in the spectral observation interval between 790 nm and 920 nm, the second Raman spectral domain extends of Dn ₃ = 1835 cm ^-1 at Dn ₄ = 3623 cm ^-1 . In other words, the computer converts the second Raman signal expressed in wavelength into a second part of Raman spectrum expressed in relative wavenumber.

 According to a variant, the computer 12 retains the first portion of the Raman scattering spectrum and the second portion of the Raman scattering spectrum to form a set of Raman spectra portions that can be processed later. It can also keep in this game the information of the wavelengths of excitation and the wavelength observation domain (s). The various parts of conserved Raman spectra are for example preserved in the form of vectors comprising the wavelength, the wave number, the intensity and the intensity of the background signal.

 Advantageously, the computer 12 combines the first portion of the Raman scattering spectrum and the second portion of the Raman scattering spectrum to reconstitute a Raman scattering spectrum over a relative wavelength-extended spectral domain (see the example illustrated in FIG. Figs. 11-12) and / or a spectral range with increased spectral resolution (see the example shown in Figs. 13-14).

 This combination is done in different ways. It can be accomplished by grossly assembling the first portion of the Raman scattering spectrum and the second portion of the Raman scattering spectrum to form a single Raman scattering spectrum. This scattering spectrum obtained may be continuous or discontinuous, depending on the continuity or discontinuity of the spectral domains of sampled Raman scattering spectrum portions.

Alternatively, a correction can be made to the different parts of Raman scattering spectra before their assembly. The correction may relate to a compensation of a background signal by subtracting the background signal from the signal associated with each part of the Raman scattering spectrum. It can also be a correction of the intensity Raman scattering spectrum parts taking into account the detection system 10 (previously calibrated with a test sample), the energy associated with the source system 2, the size the focal point of the source system 2 at a point of observation, the volume or the surface of the sample 6 to be characterized or the excitation wavelength. For example, in the case of a correction of the intensity as a function of the volume of the sample 6 to be characterized, the signal associated with the corrected spectrum is obtained by dividing the signal associated with each part of the Raman scattering spectrum and corrected by background signal by the volume of the sample 6. We observe a gain in intensity as a function of the signal obtained at a new excitation wavelength l _ί with respect to a reference excitation wavelength 1, which is expressed as follows: l, ⁴ / l ⁴ . The Raman spectrum portion obtained at the excitation wavelength can thus be corrected with respect to the portion of the Raman spectrum obtained at the excitation wavelength I, with the gain factor indicated above. Alternatively, when an overlap is observed between the first Raman scattering spectrum portion and the second Raman scattering spectrum portion, an average of the two Raman scattering spectrum portions is calculated and used for the final spectrum in the Raman scattering spectrum portion. recovery. Alternatively, in the overlap area, the Raman scattering spectrum portion having the best signal to noise ratio can be used. Outside the overlap area, each part of the Raman scattering spectrum is conserved, not corrected according to the possibilities introduced previously.

This combination of the different parts of the Raman scattering spectrum has the advantage of reconstituting a Raman scattering spectrum over a range of spectral range in relative wavenumber. FIGS. 11 and 12 show, for example, that when using three excitation wavelengths of 532 nm, 561 nm and 633 nm in combination with the same spectral separation and detection system limited to a spectral domain of FIG. extending from 630 nm to 740 nm, the Raman scattering spectrum (also called extended Raman spectrum or composite multispectral Raman spectrum) obtained by the combination of three parts of Raman spectra extends over a spectral range in relative wavenumber. between about 100 cm ¹ and 5200 cm ¹ .

The combination of the Raman scattering spectrum portions according to the invention also has the advantage of improving the spectral resolution in a determined Raman spectral domain. FIGS. 13 and 14 show that the use of a spectral separation system with a finer pitch diffraction grating, for example of 1200 or 1800 lines / mm, associated with the use of several excitation wavelengths , improves the spectral resolution of the Raman scattering spectra. The spectral domain over which the reconstituted Raman scattering spectrum extends remains relatively large even though it may have certain discontinuities. In connection with FIGS. 13 and 14, a conventional Raman system based on the use of an excitation wavelength of 633 nm, a dispersion system based on a lattice of FIG. diffraction of 600 lines / mm and a detection system extending between 635 nm and 1003 nm. The detection system detects for example N pixels between 635 nm and 1003 nm. This system makes it possible to obtain a Raman spectrum extending between 100 cm ¹ and 5828 cm ¹ but requires a sensitive spectrometer in the near infrared. Figures 13 and 14 show for example the use of a diffraction grating spectral separation system, for example 1200 lines / mm, with a first excitation wavelength of 633 nm, we acquire a first part between 635 nm and 798 nm, and with a second excitation wavelength of 561 nm, a second spectrum portion is acquired in the same spectral window between 635 nm and 798 nm. In other words, a first portion of Raman spectrum extending in wavelength between 100 cm ¹ and 3266 cm ¹ and a second portion of spectrum Raman extending in wavenumber between 2127 cm ¹ and 5294 cm ¹ are acquired. . The reconstituted Raman scattering spectrum obtained by combining the first and second Raman spectral portions extends over a spectral domain then extending in relative wavenumber between 100 cm ¹ and 5294 cm ¹ with an approximate spectral resolution. double that obtained with the single excitation wavelength of 633 nm, the diffraction grating of 600 lines / mm while using a narrower detection system in wavelength with a better detectivity on the domain, here in the visible, so more standard and less expensive.

Similarly, FIGS. 13-14 show, for example, the use of a diffraction grating spectral separation system, for example 1800 lines / mm with three excitation wavelengths of 633 nm, 561 nm and 532 nm. With a first excitation wavelength of 633 nm, a first spectrum portion is acquired between 635 nm and 718 nm, with a second excitation wavelength of 561 nm a second spectrum portion is acquired in the the same spectral window between 635 nm and 718 nm and with a third excitation wavelength of 532 nm is acquired a third spectrum portion in the same spectral window between 635 nm and 718 nm. In other words, a first portion of Raman spectrum extending in wavelength between 100 cm ¹ and 1870 cm ¹ is acquired, a second portion of Raman spectrum extending in wavenumber between 2127 cm ¹ and 3898 cm ¹ and a third portion of Raman spectrum extending in wavenumber between 3098 cm ¹ and 4869 cm ¹ . The Raman scattering spectrum reconstituted (also called composite multispectral Raman spectrum) obtained by the combination of the first, second and third parts of Raman spectra extends over a spectral range extending in relative wavenumber between 100 cm ¹ and 1870 cm ¹ and between 2127 cm ¹ and 4869 cm ¹ with a spectral resolution approximately triple that obtained with a single excitation wavelength of 633 nm, a diffraction grating of 600 lines / mm and using a field of observation or a control system. more limited detection in wavelength, here in the visible, so simpler, more efficient and less expensive.

The known devices for Raman spectrometry generally use a single source at a single fixed excitation wavelength. There is then obtained at once a Raman the widest possible spectrum wavenumber relative [Av _min, Av _max]. The other known configuration uses a mobile spectral separation system, for example based on a mobile diffraction grating, and makes it possible to obtain in several times a Raman spectrum better solved and extended. Thus, for the observation towards the high wave numbers, it is in certain cases, in particular for the Raman Optical Activity (ROA, presented later in this description), necessary to move or modify the spectral separation system but also to take all the optical settings and adapt the polarization analyzer for the observation of high wave numbers. The method of the invention makes it possible to obtain an extended Raman spectrum towards the high wavenesses by modifying only the excitation wavelength of the incident light beam: each excitation wavelength generates a portion of Raman spectrum in a different spectral range in relative wavenumber. A chosen set of these different parts of the Raman spectrum makes it possible to reconstruct the extended Raman spectral domain. Particularly advantageously, according to the present disclosure, the detection filter 9, the polarization device, the polarization analyzer and the spectral separation system 8 can remain fixed. This same extended domain of reconstituted Raman spectrum can be obtained with greater spectral resolution in relative wavenumber, by increasing the resolution of the original spectral separation system.

The source system 2 may be adapted to generate more than two incident light beams of excitation. In the examples of FIGS. 2 and 3, five incident excitation light beams with five excitation wavelengths of 785 nm, 690 nm, 633 nm, 532 nm and 488 nm, respectively, are generated either sequentially, either simultaneously but spatially shifted on a two-dimensional detection system. The method applied to each of the different excitation wavelengths makes it possible to generate five parts of Raman spectrum according to the relative wavenumber (or Raman shift Dn _Ka7hah ) of the spectral interval of observation to each incident light beam. excitation (v _exc ). FIG. 2 shows that, according to an exemplary embodiment, the detection filter 9 remains unchanged when the excitation wavelengths are modified. In a variant, the detection filter 9 changes as a function of the excitation wavelength. As shown in FIG. 2, it is the specific features of the instrumental configuration combining different excitation wavelengths, at least one detection filter 9 and a preferably fixed observation spectral interval, which make it possible to observe a domain extended Raman spectral, decomposed in parts, or according to another choice, to rapidly observe Raman spectral domains distant from each other with a high spectral resolution.

The Raman spectral domains associated with these spectrum portions extend respectively for the five excitation wavelengths of the example above: between 81 cm ¹ and 1869 cm ¹ , between 1835 cm ¹ and 3623 cm ¹ , between 3140 cm ¹ and 4929 cm ^1, between 6138 cm ¹ and 7928 cm ¹ and between 7833 cm ¹ and 9623 cm ^1. The use of a plurality of incident excitation wavelengths makes it possible to reconstruct an extended spectral range towards the high wavenumbers. FIG. 3 shows the different parts of spectra that make it possible to reconstitute a Raman spectral domain with a relative wavenumber between 80 cm ¹ and 9623 cm ¹ . FIGS. 13 and 14 show the different spectral parts that make it possible to reconstitute a Raman spectral domain with a relative wavenumber between 100 cm ¹ and 5828 cm ¹ .

The measurements carried out towards the high wavenesses make it possible in particular to observe the modes of combinations, of the elongation modes CH, NH and OH, but also of harmonic modes (or "overtones" according to the English terminology sometimes used ) in these high frequencies, and this with increased efficiency in our embodiment, because the Raman intensity is proportional to the power of 4 of the inverse of the excitation wavelength, and therefore increases when a shift from red to blue, that is to say towards shorter wavelengths. This is also the case for higher order harmonic modes in very high frequencies. Another example of reconstituted Raman spectral domain is proposed in the following Table I. In this example, the spectral range of observation extends between 535 nm and 615 nm. The width of the spectral observation range of 80 nm is here less than 100 nm. The source system 2 is adapted to sequentially generate five excitation wavelengths of 633 nm, 561 nm, 532 nm, 488 nm and 473 nm, respectively. The lower and upper bounds of each Raman spectral domain in relative wavenumber are calculated from the aforementioned formula (1). The following Tables I and II summarize the relative wavelength Raman spectral domains obtained for two spectral observation ranges, between 535 nm and 615 nm for Table I and between 790 nm and 920 nm for Table II:

 Table I

 Table II

FIG. 4 represents an example of Raman scattering spectra for the Stokes configuration obtained using the Raman spectrometry method described above. The ordinate axis corresponds to the intensity of the electronic signal recorded by the detection system in arbitrary units (u. A.). The abscissa axis corresponds to the observation wavelength (in nm). The different curves are associated with different excitation wavelengths of 700 nm, 710 nm, 720 nm, 730 nm, 740 nm and 750 nm, respectively. The spectral range of observation ranges here between 760 nm and 880 nm. The width of the spectral observation range is here also relatively narrow, limited to 120 nm. These different parts of Raman spectra of acetonitrile were obtained with a spectral separation system by diffraction grating, for example 830 lines / mm and a detection system comprising a CCD camera, for example 2048 pixels.

FIG. 5 represents an example of Raman scattering spectrum parts, for the Stokes configuration, in relative wavenumber corresponding to the wavelength spectra of FIG. 4. The ordinate axis corresponds to the intensity of the signal electronic recorded by the detection system in arbitrary units (ua). The abscissa axis corresponds to Raman displacement in relative wavenumber (in cm ¹ ). Each spectrum portion shown in FIG. 5 corresponds to a spectrum shown in FIG. 4. The spectrum portions of FIG. 5 are generated by the Raman displacement calculator in relative wavenumber for the same spectral observation interval as that of Figure 4 with respect to the different excitation wavelengths. The configuration of the spectral separation system and the detection system remains the same for all excitation wavelengths. The spectral range of all the Raman spectrum portions here ranges from about 0 cm ¹ to 2800 cm ¹ .

FIG. 11 represents another example of Raman scattering spectral spectra obtained using the Raman spectrometry method described previously. The different curves are associated with different excitation wavelengths of 633 nm, 561 nm and 532 nm, respectively. The spectral range of observation extends here between 630 nm and 740 nm. The width of the spectral observation range is here also relatively narrow, limited to 110 nm. These different parts of Raman spectra of alpha-pinene were obtained with a spectral separation system by diffraction grating, for example of 600 lines / mm.

FIG. 12 represents an example of relative wave number Raman scattering spectrum portions corresponding to the wavelength spectra of FIG. 11. Each spectrum portion shown in FIG. 12 corresponds to a spectrum shown in FIG. 11. The spectrum portions of FIG. 12 are generated by the Raman shift calculator in relative wavenumber for the same spectral observation interval as that of FIG. 11 with respect to the different excitation wavelengths. More specifically, a first part of Raman spectrum obtained with the excitation wavelength of 633 nm extends between 100 cm ¹ and about 2300 cm ¹ ; a second portion of Raman spectrum obtained with the excitation wavelength of 561 nm extends from 2100 cm ¹ and 4300 cm ¹ and a third portion of the Raman spectrum obtained with the excitation wavelength of 532 nm extends between about 3000 cm ¹ and 5300 cm ¹ . The configuration of the spectral separation system and the detection system remains the same for all excitation wavelengths. The spectral range of all the Raman spectrum portions here ranges from about 0 cm ¹ to 5300 cm ¹ .

In another example (not shown), the use of four excitation wavelengths of 785 nm, 685 nm, 633 nm and 561 nm makes it possible to obtain four parts of Raman spectra of chloroform and the computer makes it possible to conserve this play four parts of Raman spectra for later processing or combine these four parts of Raman spectrum to reconstitute a Raman spectrum extending from 100 cm ¹ up to 7000 cm ¹ .

 FIGS. 6 and 7 represent examples of Raman spectrum for the anti-Stokes configuration, as a function of the observation wavelength for FIG. 6 and as a function of the relative wavenumber for FIG. 7.

In FIGS. 6 and 7, the ordinate axis corresponds to the intensity of the Raman signal recorded by the detection system in arbitrary units (ua). These spectra were obtained for an observation spectral range extending between 660 nm and 780 nm, with a spectral separation system by diffraction grating, for example 830 lines / mm, and a detection system comprising a CCD camera. for example 2048 pixels. The width of the spectral observation range is here also relatively narrow, limited to 120 nm. The different curves are associated with different excitation wavelengths respectively of 788 nm, 800 nm, 820 nm and 850 nm.

Alternatively, the Raman spectrometry apparatus 1 can be used to measure non-linear Raman effects such as Hyper Raman, stimulated Raman, and anti-Stokes Raman scattering (CARS). For example, the Raman spectrometer 1 can be used to measure the Hyper Raman effect at 2 photons or more generally at n photons, where n is a natural number greater than or equal to 2. In this configuration, the source system 2 generates an incident light beam of excitation at an excitation wavelength noted at _exc . The calculator 12 is adapted to generate a portion of the Raman spectrum in an observation spectral interval, said spectral observation interval extending beside a wavelength corresponding to a fraction 1 / n of the length of the spectrum. _exc excitation wave At, for example at half the excitation wavelength in the case where n = 2. Optionally, an additional filter is disposed in the apparatus between the sample 6 and the detection system 10, to cut the corresponding wavelength that fraction 1 / n of the excitation wavelength. The computer 12 is adapted to generate a 2-photon Hyper Raman spectrum portion in a relative wavenum spectral domain:

 The relative wave number for the 2-photon hyper-Raman signal is here equal to the difference between twice the excitation wave number and the observation wave number. Here too, the relative wave number is thus formed of a linear combination of the excitation wave number and the observation wave number.

FIG. 8 represents an example of Hyper Raman scattering spectra obtained using the variant of the Raman spectrometry method described in the preceding paragraph. The ordinate axis corresponds to the intensity of the Raman signal recorded by the detection system in arbitrary units (ua). The abscissa axis corresponds to the observation wavelength (in nm). The different curves are associated with different excitation wavelengths of 1160 nm, 1180 nm, 1210 nm, 1240 nm, 1270 nm and 1300 nm, respectively. The spectral range of observation here ranges between 635 nm and 705 nm. The width of the spectral range of observation is here limited to about 70 nm for most spectra. In addition, a Raman spectrum of about 200 nm is shown for a spectrum at the excitation wavelength of 1300 nm, rotating the diffraction grating. These different spectra were obtained with a spectral separation system by diffraction grating, for example 1800 lines / mm and a detection system comprising a CCD camera, for example 2048 pixels.

FIG. 9 represents an example of parts of the Hyper Raman scattering spectrum of relative wavenumber. The ordinate axis corresponds to the intensity of the electronic signal recorded by the detection system in arbitrary units (ua). The x-axis corresponds to the Raman displacement in relative wavenumber (in cm ¹ ) in the two-photon hyper-Raman configuration (deduced from formula (3)). The spectrum portions shown in FIG. 9 correspond to the spectra shown in FIG. 8 with a modification of the abscissa axis by converting the wavelengths to relative wavenumber, the relative wavenumber being calculated for each part of the Raman spectrum as a function of the excitation wavelength specific to each excitation light beam and the observation wavelength in the observation spectral interval which remains fixed for all the lengths of excitation wave. The computer 12 generates the spectrum portions of FIG. 9 in relative wavenumber of the spectral observation interval of FIG. 8 with respect to each excitation wavelength, the configurations of the spectral separation systems and detection being identical. The Raman spectral domain (deduced from formula (3)) here extends in relative wavenumber from - 200 cm ¹ to 3300 cm ¹ .

In another variant, the Raman spectrometry apparatus 1 can be used to perform Raman Optical Activity (or ROA) measurements. There are three basic types of mounting: ICP (Incident circular polarization) mounting, SCP (Scattered Circular Polarization) mounting, and DCP (Dual Circular Polarization) mounting. The sample 6 to be analyzed is then either chiral, or of primary or secondary chiral structure. The measurement of the ROA spectrum is based on a difference of Raman signals resulting from a polarization modulation of the beam bright incident of excitation and / or scattered light beam. Figure 10 provides a schematic representation of the different elements of a Raman spectrometry apparatus 100 as part of Raman Optical Activity measurements. The elements common to Figures 1 and 10 have the same references and will not be described again below.

 The source system 2 generates a first incident light beam excitation at a first excitation wavelength. The incident excitation light beam is directed towards a polarization device 4. Said polarization device 4 comprises, for example, a polarizer and / or a prism or a half-wave or quarter-wave delay plate adapted to polarize the light beam. excitation incident is according to at least two different polarization states, for example orthogonal to each other such as for example two circular or elliptic polarization states, or in a linear polarization of random direction perpendicular to the propagation axis simulating an unpolarized beam . The incident light beam of excitation thus polarized by the polarization device 4 is then directed towards the sample 6 to be characterized.

 After the sample, the light beam is filtered by the detection filter 9. The Raman spectrometry apparatus 100 further comprises a polarization analyzer 7 adapted to analyze the filtered light beam. The polarization analyzer 7 comprises a right and / or left circular polarization diffuser or selector or a right and / or left elliptic polarization selector or a linear polarization separator located after a linear polarization circular polarization converter, for example a quarter wave plate. After the polarization analyzer 7, the beam of light scattered and analyzed in polarization is spectrally separated by the spectral separation system 8, then directed to the detection system 10. In a variant, the polarization analyzer 7 can be positioned before the polarization analyzer 7. filter in detection 9.

 Similarly to the Raman spectrometry method described above, the first excitation light beam at a first excitation wavelength polarized in a first polarization leads to the recording of a first Raman signal.

The polarization device 4 is configured to modify the polarization state of the incident light beam excitation and / or scattered, for example in the first place in a left circular polarization. According to the method of Raman spectrometry described above, a second excitation light beam at this first excitation wavelength and polarized according to a second polarization leads to the recording by the detection system 10 of a second Raman signal.

The computer 12 is adapted to generate a third Raman signal, said spectrum of Raman Optical Activity, this third signal corresponding to the difference of the first Raman signal and the second Raman signal or, in another configuration, to a linear combination of a a set of Raman spectra of different polarizations, expressed as the relative wavenumber of the excitation v _exCi with respect to the spectral range of observation [v _obS2 , v _obSl ].

 The source system 2 is adapted to generate at least two different excitation wavelengths. The method applied for each of the different excitation wavelengths makes it possible to generate at least two portions of the Raman optical activity spectrum as a function of the relative wave number of the spectral observation interval with respect to the number of wave corresponding to the excitation light beam, without changing the polarizing optical components. The use of multiple incident excitation wavelengths makes it possible either to reconstruct an extended spectral domain towards high wavenumbers, or to rapidly observe Raman spectral domains that are well resolved and remote from one another. Both solutions make it possible to complete and refine the spectral characterization of the sample 6 studied, for example chirality in the case of the Raman Optical Activity.

In another variant, the Raman spectrometry apparatus 1 can be used to perform Hyper Raman Optical Activity (or HROA) measurements. In this case, the spectrometry apparatus is declined as the variant of Raman Optical Activity, with a two photon excitation instead of one or at n photons if we observe the higher order nonlinear HROA effect. In the Hyper Raman (or HROA) configuration, only the excitation and the optical system 3 for guiding and / or collimating and / or focusing and / or shaping the beam must be adapted for a wavelength of double excitation of that used in the Raman configuration (or ROA). Optionally, an adapted additional filter can be added to cut the excitation wavelength that can noisy the Raman system, even at a wavelength much greater than the domain observation.

In another variant, the spectral separation system 8 and / or the detection filter 9 and / or the interference system and / or the detection system 10 is adapted to record a Raman spectrum, respectively ROA spectrum, associated with said first light beam scattered and detected in another spectral range of reduced wavelength observation [A _ofcS3 A _ofcs J with better resolution. By keeping the same number of detection elements, another broadcast signal is then detected and thus has a higher accuracy and spectral resolution than the first Raman signal. The computer 12 receives the other of the detection system signal 10 and generates another spectrum from said another broadcast signal according to said wavelength other spectral observation interval [A _{oi, S3,} A _{oi, s} J. The computer 12 is also adapted to generate another part of the Raman spectrum in relative wavenumber as a function of the difference between the first wavenumber associated with the first excitation light beam and the wavenumbers of said spectral range. reduced observation [v _{0bs4> Vobs3} ] _> said other spectral range extending between a fifth relative wave number Dn ₅ = v _exCi - v _obS3 and a sixth relative wave number Dn ₆ = v _exCi - v _0bS4 . In this way, as the number of sensing elements is kept in the reduced spectral range, the spectral accuracy of the Raman scattering spectrum obtained increases. In practice, the spectral accuracy increases inversely with the reduction ratio of the wavelength observation spectral interval.

In another variant, a second spectral separation system (not shown) may be added to the path of the light beam after the first spectral separation system 8, which makes it possible to reduce the spectral observation interval and thus to obtain domains Raman spectrals in relatively high relative wavenumber, typically of the order of a few tens of cm ¹ .

In another variant, the Raman spectrometry apparatus 1 makes it possible to calibrate a spectral separation system accurately and rapidly at a wavelength. For this, the source system 2 comprises a wavelength tunable laser source, or different discrete wavelengths selected. The source system is calibrated in origin or measured in wavelength with a lambdameter for example. These light beams of excitation whose wavelength is determined, are diffused by a reference sample having one or more fine and well known spectral bands. The change in excitation wavelength makes it possible to scan and calibrate the spectral range of the spectral separation system. The use of the Raman spectrometry apparatus 1 according to the invention then makes it possible to dispense with the spectral calibration lamps.

 The Raman spectrometry apparatus according to the invention can relate to all Raman spectrometers, including portable and embedded devices, which work with a fixed spectral observation interval, adapted for measurements on sites, from satellites, since the extraterrestrial probes or in the depths of the oceans. For these different applications, spectral reproducibility and the absence of moving parts is crucial for the durability of instruments and measurements.

The Raman spectrometry apparatus in accordance with the invention can also relate to Raman spectrometers for which measurements with high dynamics and high signal-to-noise ratio at high wavenumbers are desired: the spectral range of observation in length of wave for which the spectral separation and detection system is optimized, regardless of the Raman domain probed. In particular, it allows to probe higher order harmonics with very high numbers wavelength, particularly greater than 5000 cm ^1. In the same way, the invention also makes it possible to quickly probe with high resolution several Raman spectral domains narrow and far apart in relative wave number with these same efficiency advantages.

The present invention makes it possible to probe Raman Stokes spectral domains of relative wavenumber well above the initial observation wavenumber: for example, if the observation is located around 10000 nm (1000 cm ¹ ), by exciting at 1000 nm (10000 cm ^1), the invention makes it easy to measure a very high wave number spectrum to 9000 cm ^1, wherein are located the third harmonics of the CH stretch modes.

In addition, when the fluorescence parasitic Raman spectra, the use is to favor a laser excitation in the near infrared at 785 nm and 1064 nm. Unfortunately, at these exciting wavelengths, the detection of high wavenesses, such as CH elongations (stretching 3000 cm ¹ ) and beyond drastically, because of the low efficiency of the detection systems: this amounts to observing the infrared domains (respectively 1030 nm and 1563 nm). The present invention retaining essentially the same nm observation range on at least one overlap zone and the optimized efficiency of the spectral separation system and the detection system makes it easy to measure these high relative wave numbers while increasing the Raman effect (proportional to Ml _ece ) and always avoiding the fluorescence which remains confined in the same emission spectral domain in nm whatever the exciter wavelength.

Claims

1. Raman spectrometry apparatus (1; 100) for characterizing a sample (6), the apparatus (1; 100) comprising a source system (2) generating a first incident excitation light beam at a first length of excitation wave, a spectral separation system (8) receiving a first scattered light beam formed by scattering said first incident excitation light beam onto the sample (6) and spectrally separating said first scattered light beam, a detection system _Apparatus (10) for recording a first Raman signal associated with said first scattered and detected light beam in a wavelength observation spectral range extending between a first observation wavelength (At _obSi ) and a second observation wavelength {l _oύå2 ), a calculator (12) receiving the first Raman signal of said detection system (10) and generating a first portion of Raman spectrum according to the d Raman shifting in a first Raman spectral domain in relative wavenumber, said first Raman spectral domain extending between a first relative wavenumber according to the first wavelength of excitation and the first wavelength of observation and a second relative wave number according to the first excitation wavelength and the second observation wavelength;

characterized in that

said source system (2) is adapted to generate at least a second excitation incident light beam at a second excitation wavelength, said second excitation wavelength being different from the first wavelength excitation circuit, said spectral separation system (8) being adapted to receive a second scattered light beam formed by scattering said second excitation incident light beam onto the sample (6) and to spectrally separate said second scattered light beam, said detection system (10) being adapted to detect and record a second Raman signal associated with said second light beam scattered in the same wavelength observation spectral range, said computer (12) being adapted to measure the second Raman signal and to generate a second part of Raman spectrum according to Raman displacement in a second Raman spectral domain in relative wavenumber, said second Raman spectral domain extending between a third relative wavenumber according to the second excitation wavelength and the first observation wavelength and a fourth relative wavenumber function of the second excitation wavelength and the second wavelength of observation, the second Raman spectral domain being different from the first Raman spectral domain in relative wavenumber, the first Raman spectrum portion and the second Raman spectrum portion being intended to be combined to reconstruct a Raman scattering spectrum over an extended spectral range in relative wavenumber and / or having an increased spectral resolution in the first and / or second domain spectral Raman.

 The Raman spectrometry apparatus (1; 100) according to claim 1, wherein the source system (2) is adapted to generate a plurality of excitation light beams at a plurality of excitation wavelengths.

 Raman spectrometry apparatus (1; 100) according to claim 1 or 2, wherein the source system (2) comprises a plurality of monochromatic laser sources, an optical frequency tunable laser source and / or a multi-length generating source. Monochromatic excitation wave waves selectable or spatially separable.

 Raman spectrometry apparatus (1; 100) according to one of claims 1 to 3, wherein the source system (2) comprises a continuous or pulsed laser source.

 5. Raman spectrometry apparatus (1; 100) according to any one of claims 1 to 4, further comprising at least one polarization device (4) of the excitation light beam between the source system (2) and the sample (6), said polarization device (4) being adapted to bias the first excitation incident light beam according to at least two different polarization states and respectively the second excitation incident light beam according to at least two states of different polarization.

The Raman spectrometry apparatus (100) according to one of claims 1 to 5, further comprising a polarization analyzer (7) disposed between the sample (6) and the detection system (10), the analyzer of polarization (7) being adapted to analyze and / or polarize the first scattered light beam and, respectively, the second scattered light beam.

The Raman spectrometry apparatus (1; 100) according to any one of claims 1 to 6, wherein the computer (12) is configured to hold the first Raman scattering spectrum portion and the second scattering spectrum portion. Raman and constitute a set of parts of Raman spectra or to combine the first portion of Raman spectrum and the second part of Raman spectrum and reconstruct an extended Raman spectrum and / or increased spectral resolution in relative wave number.

 Raman spectrometry apparatus (1; 100) according to any of claims 1 to 7, wherein the calculator (12) is adapted to generate a first, respectively second, part of a hyper-Raman scattering spectrum in a first, respectively second, a relative wavelength hyper Raman displacement spectral domain, wherein the first relative wavenumber is equal to the difference between a product of an integer n and the first excitation wavenumber and the first observation wave number, the second relative wave number is equal to the difference between a product of the integer n and the first excitation wave number and the second observation wave number, the third relative wave number is equal to the difference between a product of the integer n and the second excitation wave number and the first observation wave number, the fourth relative wave number is equal to al to the difference between a product of the integer n and the second excitation wave number and the second observation wave number, the integer multiple n being greater than or equal to two.

 9. Raman spectrometry apparatus (1; 100) according to one of claims 1 to 8, comprising a detection filter (9) configured to cut the first excitation wavelength and / or the second wavelength. excitation.

 10. Raman spectrometry apparatus (1; 100) according to one of claims 1 to 9, wherein the detection filter (9) comprises at least one high-pass filter, a low-pass filter or a band-pass filter. or a combination of said filters.

11. Raman spectrometry apparatus (1; 100) according to one of claims 1 to 10, wherein the spectral separation system (8) comprises a spectrometer based on diffraction grating (s), prism (s) and / or grism (s) or a spectrometer comprising a combination of network (s) of diffraction and / or prism (s) and / or grism (s).

 Raman spectrometry apparatus (1; 100) according to one of claims 1 to 11, wherein the spectral separation system (8) comprises an interference filter and / or an interferometer.

 13. Raman spectrometry apparatus (1; 100) according to one of claims 1 to 12, wherein the detection filter (9) is fixed.

 The Raman spectrometry apparatus (1; 100) according to one of claims 1 to 13, wherein the detection system (10) comprises a single-channel detector or a one-dimensional linear detector or a two-dimensional matrix detector.

 15. Raman spectrometry method comprising the following steps:

generating a first excitation incident light beam at a first excitation wavelength by a source system (2);

 spectral separation of a first scattered light beam formed by scattering the first excitation incident light beam onto a sample (6);

 recording of a first Raman signal associated with the first scattered light beam, detected in a spectral wavelength observation range extending between a first observation wavelength and a second wavelength of observation;

 calculating a first portion of Raman spectrum as a function of the Raman displacement in a first Raman spectral domain in relative wave number, said first Raman spectral domain extending between a first relative wave number and a function of the first length of the Raman spectrum. excitation wave and the first observation wavelength and a second relative wave number according to the first excitation wavelength and the second observation wavelength;

 generating at least one second excitation incident light beam at a second excitation wavelength by the source system (2), said second excitation wavelength being different from the first excitation wavelength; excitation wave;

 spectral separation of a second scattered light beam formed by diffusion of the incident incident light beam onto the sample (6);

recording of a second Raman signal associated with the second scattered light beam, detected in the same spectral observation range in wavelength;

 calculating a second portion of Raman spectrum as a function of the Raman displacement in a second Raman spectral domain in relative wave number, said second Raman spectral domain extending between a third relative wave number and a function of the second length of excitation wave and the first observation wavelength and a fourth relative wave number according to the second excitation wavelength and the second observation wavelength, the second domain Raman spectral being different from the first Raman spectral domain in relative wavenumber; and

 combining said first portion of the Raman scattering spectrum and said second portion of the Raman scattering spectrum to reconstitute a Raman scattering spectrum over an extended spectral range in relative wavenumber and / or having an increased spectral resolution in the first and / or second Raman spectral domain.