HK1187400B - Device and method for observing and for measuring raman scattering - Google Patents

Description

The present invention relates to the field of Raman spectrometry. More specifically, the invention relates to a visualization device and method for a Raman spectrometer.

Since the arrival of laser sources, Raman spectroscopy has experienced tremendous growth and now finds applications in a wide variety of fields, ranging from fundamental research to industrial process control applications.

Raman spectroscopy is based on the measurement of transitions between vibrational states of a polyatomic, molecular or ionic structure (and on rotational states in the case of gases), regardless of the physical state of the sample (gas, liquid, amorphous or crystalline solid). A sample illuminated by a monochromatic light source (a laser) scatters light that is no longer monochromatic but exhibits scattering bands at different frequencies. Thus, the spectrum obtained is composed of three scattering sources: the Rayleigh (elastic scattering), Stokes and Anti-Stokes (inelastic scattering) bands. Raman frequencies are specific for each sample and are independent of the laser frequency. Raman spectroscopy thus allows non-destructive chemical analysis of solids, liquids, powders or gases.

More recently, the miniaturization of optical components has made it possible to couple Raman spectrometry with standard optical microscopy to enable the analysis of samples with micrometer spatial resolution. The excitation laser beam is generally focused by an objective or optical lens. Different Raman spectrometry devices have a viewing system that illuminates the sample and forms an image of the sample on a screen. A viewing system is generally based on the use of a white light source (conventional lamp), a viewing camera and a retractable optical component, such as a semi-transparent slide, on the optical path of the measuring instrument. The positioning of the viewing device allows the sample to be focused before measurement, for example using an autofocus system. In such a device, to perform a Raman spectrometry measurement of the sample, the illumination and viewing device must be removed from the optical path, for example by retracting the semi-transparent slide out of the optical path. However, such a device can present handling difficulties. Indeed, the use of a retractable optical component requires a mechanical movement that leads to a risk of movement. In addition, the lack of reproducibility of the opto-mechanical movement can produce a different focus of the sample seen by the viewing system and by the Raman measurement system.

In some applications, it is desirable to track the sample over time and it is useful to be able to visualize the sample during a series of Raman measurements. In some particular applications, it may even be necessary to perform or adjust the focus on the sample simultaneously with the measurement. However, using an illumination device during the Raman measurement may disturb the measurement of the Raman signals. First, the excitation laser is likely to generate stray light in the direction of the viewing camera, which may saturate the camera sensor and prevent correct visualization of the sample. In addition, the permanent presence of an additional optical component, such as a semi-transparent plate, in the optical path necessarily leads to a decrease in the detected Raman signal. Finally, the illumination source is likely to generate stray light by scattering not only on the sample but also on the internal components of the device and thus disturb the measurement of the Raman signals. However, the difficulty in measuring Raman signals comes mainly from the very low intensity of Raman scattering compared to the intensity of Rayleigh scattering. It is therefore not possible, with current systems, to simultaneously perform a Raman measurement and visualize a sample. Patent documents WO2008052221 , WO2004081549 And WO2010/024397 propose to combine a Raman spectrometry measurement system having an excitation source in the near infrared range with an imaging system based on white light illumination.

One of the aims of the invention is to provide a device and a method for Raman visualization and spectrometry.

An aim of the invention is to provide a device and a method allowing simultaneous visualization and measurement by Raman spectrometry of a sample. The present invention aims to overcome these drawbacks and relates more particularly to an optical device for Raman spectrometry and visualization of a sample according to claim 1.

• un filtre optique apte à réfléchir ledit faisceau laser d'excitation de bande spectrale B0 et à transmettre ledit faisceau de visualisation de bande spectrale BV ;
• un filtre optique apte à transmettre ledit faisceau laser d'excitation de bande spectrale B0 et à réfléchir ledit faisceau de visualisation de bande spectrale BV;
• ledit premier moyen de filtrage comprend un filtre optique apte à réfléchir ledit premier faisceau secondaire et à transmettre ledit deuxième faisceau secondaire ;
• ledit premier moyen de filtrage comprend un filtre optique apte à transmettre ledit premier faisceau secondaire et à réfléchir ledit deuxième faisceau secondaire ;
• ledit deuxième moyen de filtrage comprend un filtre optique apte à réfléchir ledit premier faisceau tertiaire et à transmettre ledit deuxième faisceau tertiaire ;
• ledit deuxième moyen de filtrage comprend un filtre optique apte à transmettre ledit premier faisceau tertiaire et à réfléchir ledit deuxième faisceau tertiaire
• ledit filtre optique est choisi parmi un filtre passe-haut, passe-bas, passe-bande ou coupe-bande ;

According to various particular aspects of the invention, said optical superposition means comprise:

• an optical filter capable of reflecting said excitation laser beam of spectral band B0 and of transmitting said viewing beam of spectral band BV;
• an optical filter capable of transmitting said excitation laser beam of spectral band B0 and of reflecting said viewing beam of spectral band BV;
• said first filtering means comprises an optical filter capable of reflecting said first secondary beam and transmitting said second secondary beam;
• said first filtering means comprises an optical filter capable of transmitting said first secondary beam and of reflecting said second secondary beam;
• said second filtering means comprises an optical filter capable of reflecting said first tertiary beam and transmitting said second tertiary beam;
• said second filtering means comprises an optical filter capable of transmitting said first tertiary beam and of reflecting said second tertiary beam
• said optical filter is chosen from a high-pass, low-pass, band-pass or band-stop filter;

• des moyens de réglage d'autofocus, et/ou
• des moyens de stabilisation d'image couplés à des moyens de déplacement relatif de l'objet par rapport au faisceau d'excitation laser.

According to particular aspects, the device of the invention further comprises:

• autofocus adjustment means, and/or
• image stabilization means coupled with means for relative movement of the object with respect to the laser excitation beam.

The invention also relates to a Raman spectrometry method according to claim 11.

• la figure 1 représente schématiquement une répartition spectrale de l'intensité du faisceau laser d'excitation, du faisceau d'éclairage et de visualisation et du faisceau de diffusion Raman ;
• la figure 2 représente schématiquement un exemple de réalisation d'un dispositif de l'invention illustrant le chemin optique des différents faisceaux incidents et diffusés ;
• La figure 3 représente un dispositif selon un mode de réalisation préféré de l'invention ;
• la figure 4 représente schématiquement les spectres en intensité des composants utilisés dans le dispositif de la figure 3 ;
• la figure 5 représente un premier cas de répartition des bandes spectrales; ce cas ne faisant pas partie de l'invention;
• les figures 6 à 9 représentent différents modes de réalisation, ne faisant pas partie de l'invention, utilisant la répartition des bandes spectrales de la figure 5 ;
• la figure 10 représente un deuxième cas de répartition des bandes spectrales, selon l'invention;
• les figures 11 à 18 représentent différents modes de réalisation de l'invention utilisant la répartition des bandes spectrales de la figure 10 ;
• la figure 19 représente un troisième cas de répartition des bandes spectrales; ce cas ne faisant pas partie de l'invention;
• les figures 20 à 23 représentent différents modes de réalisation, ne faisant pas partie de l'invention, utilisant la répartition des bandes spectrales de la figure 19 ;
• la figure 24 représente un quatrième cas de répartition des bandes spectrales; ce cas ne faisant pas partie de l'invention;
• les figures 25 à 28 représentent différents modes de réalisation, ne faisant pas partie de l'invention, utilisant la répartition des bandes spectrales de la figure 24.

This description given by way of non-limiting example will make it easier to understand how the invention can be implemented with reference to the appended drawings in which:

• Figure 1 schematically represents a spectral distribution of the intensity of the excitation laser beam, the illumination and visualization beam and the Raman scattering beam;
• Figure 2 schematically represents an exemplary embodiment of a device of the invention illustrating the optical path of the different incident and scattered beams;
• Figure 3 represents a device according to a preferred embodiment of the invention;
• Figure 4 schematically represents the intensity spectra of the components used in the device of Figure 3;
• Figure 5 represents a first case of distribution of the spectral bands; this case is not part of the invention;
• Figures 6 to 9 represent different embodiments, not forming part of the invention, using the distribution of the spectral bands of Figure 5;
• Figure 10 represents a second case of distribution of the spectral bands, according to the invention;
• Figures 11 to 18 represent different embodiments of the invention using the distribution of spectral bands of Figure 10;
• Figure 19 represents a third case of distribution of the spectral bands; this case is not part of the invention;
• Figures 20 to 23 represent different embodiments, not forming part of the invention, using the distribution of the spectral bands of Figure 19;
• Figure 24 represents a fourth case of distribution of the spectral bands; this case not being part of the invention;
• Figures 25 to 28 represent different embodiments, not forming part of the invention, using the distribution of the spectral bands of Figure 24.

The invention proposes an arrangement of filters allowing Raman and visualization of the sample without moving parts and simultaneously.

The idea is to use a specific spectral range for illumination and visualization of the sample, this spectral range being disjoint from that of the laser and the induced Raman range.

There figure 1 represents very schematically the spectral distribution of the intensity of different measurement and visualization beams. The excitation laser beam has a wavelength λ ₀ and a spectral band B ₀ centered on the wavelength λ ₀ , the spectral band B ₀ being very narrow. The excitation beam (1) generates by Raman scattering on a sample a Raman scattering beam whose lines are located in a spectral band B _R represented schematically by the curve (3) on the figure 1 .

One aspect of the invention consists in using a viewing beam having a spectral band B _V distinct from the spectral band B ₀ of the laser and from the spectral band B _R which one seeks to measure.

There figure 2 schematically represents an exemplary embodiment of a device according to an embodiment of the invention so as to illustrate the path of the different beams. The device of the figure 2 allows to superimpose an incident laser beam and an incident illumination beam and simultaneously to separate the beam scattered by the sample (7) and collected by the objective (6) according to its different spectral components, more precisely according to the spectral bands B ₀ , B _V and B _R . The beam (21) is a backscattering beam of the excitation laser having a spectral band B ₀ (Rayleigh scattering). The beam (3) is the Raman scattering beam which has a spectral component B _R . The viewing beam (22) is a Rayleigh backscattering beam of the illumination beam (2) which has a spectral component B _v . The filter (12) transmits the Raman scattering beam (3) and reflects the Rayleigh scattering beams (21) and (22). The filter (13) transmits the viewing beam (22) scattered by the sample (7) and reflects the Rayleigh scattering beam at the laser wavelength. A splitter blade (16) transmits the viewing beam (22) scattered by the sample, for example, towards a viewing camera (not shown). The Raman beam (3) can be transmitted towards a Raman spectrometer in order to provide the measurement of the Raman lines in the spectral band B _R . The device of the figure 2 thus allows the sample to be viewed using the viewing beam (22) and simultaneously to carry out a Raman measurement using the Raman scattering beam (3) which is separated from the Rayleigh scattering of the laser beam and the illumination beam.

There figure 3 represents a device according to a preferred embodiment of the invention. The device of the figure 3 can be coupled directly to a Raman spectrometer or remote from the Raman spectrometer to be placed as close as possible to the sample, the device then being connected to a Raman spectrometer by optical fibers. The housing (20) comprises an input (10) for coupling an excitation laser beam and directing it towards a first deflecting mirror (14). The laser beam (1) is transmitted by the filter (13) then reflected by the filter (12) to be transmitted towards the sample through the optical focusing component (15). The housing (20) comprises a display source (11) which is for example a green LED emitting in a wavelength range between 500 and 550 nm. The display source (11) generates a display beam (2) which is directed towards a splitter plate (16), then transmitted towards the filter (13). The filter (13) reflects the beam (2) towards the filter (12) which also reflects the viewing beam (2) towards the sample, so as to superimpose it on the laser excitation beam (1). The scattering beam collected through the porthole (15) comprises a Raman scattering beam (3) which is transmitted by the filter (12) towards a module (18) which can be either a Raman spectrometer or a fiber connector so as to transmit the Raman beam (3) towards a remote Raman spectrometer. The beam scattered by the sample at the wavelength λ ₀ of the laser is reflected by the filter (12), transmitted by the filter (13) and redirected towards the input/output (10). The collected beam also comprises a component in the B _V spectral band of the viewing source. The backscattered viewing beam (22) is reflected by the filter (12) and by the filter (13) then transmitted by the splitter plate (16). This viewing beam (22) is directed towards a viewing camera (17).

A prototype of a remote fiber probe, based on the diagram of the figure 3 was made for an excitation laser having a wavelength λ ₀ of 660nm, but this principle can be applied to any device. The filter (12) reflects the laser (660nm), the low-wavelength illumination (less than 660 nm) and the light reflected by the sample. The filter (12) transmits the Raman scattering beam for wavelengths from 665 nm, the Raman range extending in wavenumber between 400 and 3500 cm ^-1 . The filter (13) transmits the excitation laser at 660nm and reflects the low-wavelength illumination beam. The splitter plate (16) separates the illumination beam (2) which goes from the illumination source to the sample from the viewing beam (22) which goes from the sample to a viewing camera. The device of the figure 3 is compatible with a confocal video system. The excitation laser is coupled to the input connector (10) via an optical fiber with a core diameter of 5-6 microns. The probe is connected to a Raman spectrometer via an optical fiber with a core diameter of approximately 100 microns. The illumination source is a green LED with an aperture of 15° and a light intensity of approximately 6800 mcd.

There figure 4 schematically represents the relative spectral response of the different sources and filters used. The laser beam (1) has a wavelength λ ₀ and a very narrow spectral band B _0. Curve (2) corresponding to the emission spectral curve of the viewing source (11) is observed. The spectral detection curve of the viewing camera (17) has a very broad spectrum with maximum sensitivity around the spectral band B _V of the viewing source. Filter (12) is a long-pass filter with a cut-off wavelength located just above the wavelength λ ₀ of the laser while filter (13) lets the laser wavelength pass and reflects the wavelengths in the viewing spectral band B _V.

THE figures 1 to 4 describe the principle of the invention in connection with a particular embodiment of the invention. However, numerous variants based on the same principle are valid and will be developed in the examples detailed in the figures 5 to 28 depending on the respective positions of the different spectral bands of visualization B _V , laser excitation B ₀ and Raman scattering B _R .

There Figure 5 schematically represents a first case, not forming part of the invention, according to which the excitation wavelength λ ₀ defines a spectral band B ₀ . The aim is to measure Raman scattering lines in the spectral band B _R corresponding to the Stokes lines, i.e. having wavelengths greater than the excitation wavelength of the laser λ ₀ . The viewing spectral band B _V is located at wavelengths shorter than the excitation wavelength λ ₀ . For example, the laser may have a wavelength of 660 nm and the viewing may be carried out in the blue-green-yellow region of the visible spectrum.

On the figures 6 to 9 , the excitation laser beam (1) is represented by a solid line and the Stokes Raman scattering beam (3) by a dash-dot line. In the rest of the document, a common dashed line (2) represents the illumination beam incident on the sample and the viewing beam scattered by the sample, which are superimposed on the outward and return path to a splitter plate (16) not shown.

There figure 6 represents a first embodiment, not forming part of the invention, using the distribution of the spectral bands of the Figure 5 . The laser excitation beam (1) is transmitted by a filter (13a) and then reflected by a filter (12a) towards a focusing objective (6). The viewing beam (2) is reflected by the filter (13a) and then by the filter (12a) towards the objective (6). The collected beam includes the Raman scattering beam (3) which is transmitted by the filter (12a). The collected scattered beam also includes a viewing beam which is reflected by the filter (12a) and then by the filter (13a). The filter (13a) is a high-pass or band-pass filter having a cut-off wavelength located between the viewing band B _V and the band B ₀ of the laser. The filter (12a) is a high-pass filter having a cut-off wavelength located between the wavelength λ ₀ of the laser and the band B _R of Raman scattering. The filter (13a) is therefore used to superimpose the laser excitation beam and the illumination beam in the direction of the sample and on the scattering beam to separate the viewing beam from the backscattering at the laser wavelength. The filter (12a) is used to separate on the one hand the Raman scattering beam (3) and on the other hand the spectral components of the scattering beam in the spectral band B ₀ of the laser and in the spectral band B _V of the viewing beam.

There figure 7 represents a second embodiment of a device, not forming part of the invention, still using the spectral distribution according to the diagram of the Figure 5 . Unlike the figure 6 , the laser beam (1) is first reflected by a filter (13b) before being reflected on a filter (12b). Symmetrically the illumination beam (2) is transmitted by the filter (13b) before being reflected by the filter (12b). The scattered and collected beam is directed towards the first filter (12b) which transmits the Raman scattering beam (3) and reflects the components of the scattered beam in the spectral band B ₀ of the laser and in the spectral band B _V of the viewing beam 2. The filter (13b) separates the scattered viewing beam from the beam scattered at the wavelength of the laser. As in the figure 6 , the filter (12b) is a high-pass filter having a cut-off wavelength between the laser wavelength λ ₀ and the Raman spectral band B _R . The filter (13b) is a low-pass or band-stop filter having a cut-off wavelength between the viewing spectral band B _V and the spectral band B ₀ which transmits the beam in the spectral band B _V and reflects a beam having wavelengths in the spectral band B ₀ .

There figure 8 schematically represents a third embodiment, not forming part of the invention, based on the spectral distribution of the diagram of the Figure 5 . The excitation laser beam (1) is transmitted through a filter (13c) and then through a filter (12c) towards the objective (6). The illumination beam (2) is reflected on the filter (13c) and transmitted by the filter (12c). The Raman scattering beam (3) is reflected by the filter (12c). The scattering beam (2) in the viewing spectral band B _V is transmitted by the filter (12c) and reflected by the filter (13c). The filter (13c) is a long-pass or band-pass filter having a cut-off wavelength located between the spectral band B _V and the band B ₀ which transmits the band B ₀ and reflects the band B _V . The filter (12c) is a low-pass filter having a cutoff wavelength between the B ₀ band and the Raman B _R band which transmits the wavelength of the B _V spectral band and the B ₀ spectral band and reflects a beam having wavelengths in the B _R spectral band.

There figure 9 represents a fourth embodiment, not forming part of the invention, following the spectral distribution of the diagram of the Figure 5 . The device comprises a filter (12d), a filter (13d) and an objective (6). The excitation laser beam (1) is reflected on the filter (13d) and then transmitted by the filter (12d) towards the objective (6). The illumination and viewing beam (2) is transmitted by the filter (13d) and the filter (12d). The collected Raman scattering beam (3) is reflected by the filter (12d) while the scattering beam in the spectral band B _V of the viewing beam is transmitted by the filter (12d) and by said filter (13d). The filter (13d) is a low-pass or band-stop filter having a cut-off wavelength located between the viewing band B _V and the band B ₀ of the laser which transmits the viewing band B _V and reflects the band B ₀ . The filter (12d) is a low-pass filter which transmits the bands B ₀ and B _V and reflects the Raman scattering band B _R . The filter (12d) has a cut-off wavelength between the B ₀ band and the B _R band.

There figure 10 represents a case of distribution of the spectral bands according to the invention: the laser excitation spectral band, the Raman Stokes measurement bands (spectral band B _R ) and Raman anti-Stokes (spectral band B _R ^aS ) and the Bv display band.

For example, the wavelength λ ₀ of the excitation laser is located at 473nm while the viewing spectral band B _V is located in the yellow-red part of the visible spectrum, for example in a wavelength range above 600nm.

The Stokes Raman band is located at wavelengths greater than the laser excitation wavelength λ ₀ and less than a wavelength λ ₁ itself less than the B _V viewing band.

The Anti-Stokes Raman scattering band is located at wavelengths below the laser excitation wavelength λ ₀ .

The configurations illustrated on the figures 11, 12, 13 , 14 , 17 and 18 allow either Raman Stokes measurements alone or simultaneous Raman Stokes and anti-Stokes measurements to be performed as detailed later.

There figure 11 represents a first embodiment according to the spectral distribution of the figure 10 .

We will first describe the method of realization of the figure 11 for the measurement of Stokes lines alone and then for the measurement of Stokes and Anti-Stokes lines.

• Figure 11 configuration for Stokes mode

The excitation laser beam (1) is transmitted by a filter (13e) and reflected by a filter (12e). The illumination and viewing beam (2) is transmitted by the filter (12e) which retransmits the beam scattered in the viewing band B _V .

Filter (12e) reflects the Raman scattering beam (3). Filter (13e) reflects the Raman scattering beam (3).

In the Stokes configuration, the filter (13e) is a low-pass filter which transmits the B ₀ band and reflects the B _R band which therefore has a cut-off wavelength located between the B ₀ band and the B _R band.

Filter (12e) is a high-pass filter that transmits the B _V viewing band and reflects the B ₀ and B _R spectral bands.

The filter (12e) is a filter having a cut-off wavelength between the Raman band B _R and the viewing band B _V .

• Figure 11 configuration for Stokes and anti-Stokes mode

In the configuration of the figure 11 where we want to measure both the Stokes and Anti-Stokes lines, the filter (13e) is a band-pass filter which transmits the B ₀ band and reflects the Raman B _R Stokes bands and the Raman Anti-Stokes B _R ^aS band

• Configuration of Figure 12

There figure 12 schematically represents a second embodiment based on the spectral distribution of the diagram of the figure 10 . The device of the figure 12 comprises a filter (13f) which reflects the laser excitation beam (1). The illumination and viewing beam (2) is transmitted by the filter (12f) which reflects the scattered Raman beam (3) and transmits the portion of the scattered beam in the viewing band B _V . The filter (13f) separates the Raman beam (3) from the Rayleigh scattered beam at the laser wavelength. The filter (12f) is a long-pass filter which transmits the viewing band B _V and reflects the spectral bands B ₀ and B _R and has a cut-off wavelength located between B _R and B _V .

The filter (13f) transmits the Raman scattering spectral band B _R and reflects the B ₀ band of the laser. In the case where we only want to measure the Stokes Raman scattering band, the filter (13f) is a high-pass filter with a cut-off wavelength located between the B ₀ and B _R spectral bands. In the case where we want to simultaneously measure the Stokes and anti-Stokes Raman scattering lines, the filter (13f) is a band-stop filter which reflects the B ₀ spectral band of the excitation beam and transmits the Stokes Raman scattering bands B _R and Anti-Stokes B _R ^aS .

There figure 13 represents a third embodiment according to the spectral distribution of the figure 10 .

The filter (12g) superimposes the laser excitation beam (1) and the illumination and viewing beam (2) by reflecting the laser beam (1) and transmitting the illumination and viewing beam (2) in the B _V spectral band. The filter (12g) transmits the viewing beam in the B _V spectral band and the Raman scattering beam (3) and reflects the Rayleigh scattering beam in the B ₀ spectral band.

The filter (13g) transmits the viewing beam (2) in the B _V spectral band and reflects the Raman scattering beam (3). The filter (13g) is a long-pass filter having a cutoff wavelength located between the Raman spectral band B _R and the viewing band B _V so as to transmit the viewing band B _V and reflect the spectral band B _R .

In the case where we wish to measure only the Raman spectral band of the Stokes lines, the filter (12g) is a high-pass filter which transmits the spectral band B _R , the spectral band B _V and reflects the spectral band B ₀ .

In the case where we want to measure both the Stokes and Anti-Stokes lines, the filter (12g) is a band-stop filter which reflects the B ₀ spectral band, transmits the anti-Stokes Raman spectral band, the Stokes Raman spectral band and the B _V viewing spectral band.

There figure 14 represents a fourth embodiment according to the spectral distribution of the figure 10 .

The filter (12h) allows the excitation laser beam (1) and the illumination and visualization beam (2) to be superimposed towards the sample.

On the collected scattered beam the filter (12h) reflects the signal scattered by Rayleigh scattering in the spectral band B ₀ , transmits the viewing beam in the spectral band B _V and the Rayleigh scattering beam in the spectral band B _R or B _R ^as .

The filter (13h) is a low-pass filter which transmits the Raman scattering band B _R and reflects the viewing spectral band B _V .

In the case of a measurement of Stokes lines only, the filter (12h) is a high-pass filter having a cut-off wavelength between the spectral band B ₀ and the spectral band B _R so as to reflect the spectral band B ₀ and to transmit the spectral bands B _R and B _V .

In the case where we wish to measure the Stokes lines and the Anti-Stokes lines, the filter (12h) is a band-stop filter which reflects the spectral band B ₀ and transmits the spectral bands B _R Stokes B _R ^aS anti-Stokes as well as the lines of the visualization spectral band B _V .

There figure 15 represents a fifth embodiment for a measurement of the Raman Stokes lines following the distribution of the figure 10 .

The filter (13i) makes it possible to superimpose the excitation laser beam (1) and the illumination and visualization beam (2) in the direction of the object 6 and the sample.

The filter (12i) transmits both the laser excitation beam (1) and the viewing beam (2).

On the collected scattering beam, the filter (12i) separates the Raman scattering beam (3) from the viewing beam (2). The filter (13i) reflects the viewing beam (2) and transmits the Rayleigh scattered beam at the laser wavelength.

Filter (13i) is a low-pass filter that transmits the B ₀ band and reflects the Bv band.

The filter (12i) is a wide band-stop filter that transmits the B ₀ band, reflects the Raman B _R band and transmits the B _V viewing band.

There figure 16 represents another embodiment for the measurement of Raman Stokes lines alone, following the spectral distribution of the Fig. 10 .

The device of the figure 16 comprises a filter (13j) which makes it possible to superimpose the excitation laser beam (1) and the display beam by reflecting the laser beam in the spectral band B ₀ and transmitting the display beam in the spectral band B _V .

The 12j filter simultaneously transmits the excitation beam and the illumination and visualization beam (2).

The filter (12j) reflects the Raman scattering beam (3) in the spectral band B _R and transmits the Rayleigh scattering beam at the laser wavelength in the spectral band B ₀ as well as the viewing beam (2) scattered by the sample in the spectral band B _V .

The filter (13j) separates the viewing beam (2) in the spectral band B _V from the Rayleigh scattering beam in the spectral band B ₀ .

Filter (12j) is a wide band-stop filter that transmits the spectral band B _{0 ,} reflects the Raman spectral band B _R and transmits the viewing band B _V .

Filter (13j) is a high-pass filter having a cutoff wavelength between the spectral band B ₀ and the viewing band B _V .

There figure 17 represents another embodiment related to the spectral distribution of the diagram of the figure 10 The device comprises a filter (12k) which allows the laser excitation beam (1) and the viewing beam (2) to be superimposed by transmitting the beam in the spectral band B ₀ and reflecting the beam in the spectral band B _V .

The collected scattering beam includes a spectral component in the B _V viewing band which is reflected by the (12k) filter. The (12k) filter is a low-pass filter which transmits the B ₀ spectral band and the B _R Raman scattering spectral band and reflects the B _V spectral band.

The filter (13k) transmits the Raman scattering beam (3) in the Raman spectral band and reflects the Rayleigh scattering beam in the B ₀ spectral band. For the measurement of the Stokes lines the filter (13k) can be a long-pass filter with a cut-off wavelength located between the B ₀ spectral band and the Raman Stokes spectral band B _R . For the simultaneous measurement of the Stokes and Anti-Stokes lines the filter (13k) is a band-stop filter which reflects the B ₀ spectral band and transmits the Raman Stokes scattering spectral bands B _R and Anti-Stokes B _R ^aS .

There figure 18 represents another embodiment for a spectral distribution following the path of the figure 10 .

The device comprises a filter (12ℓ) which allows the laser excitation beam and the viewing beam (2) to be superimposed by transmitting the laser excitation beam (1) and reflecting the viewing beam (2).

On the scattering beam, the filter (12ℓ) allows the viewing beam to be extracted in the B _V viewing spectral band and transmits the Raman scattering signal in the B _R band as well as the Rayleigh scattering signal in the B ₀ spectral band. The filter (12ℓ) is a low-pass filter which transmits the B ₀ band and the B _R band and reflects the B _V band and therefore has a cut-off wavelength located above the λ ₀ wavelength between the Raman B _R band and the B _V viewing spectral band.

The filter (13ℓ) reflects the Raman scattering signal and transmits the Rayleigh scattering signal in the B ₀ spectral band. For the measurement of Stokes Raman lines only, the filter (13ℓ) is a low-pass filter that transmits the B ₀ spectral band and reflects the B _R Raman spectral band. In the case where one wishes to measure the Stokes and Anti-Stokes Raman scattering lines simultaneously, the filter (13ℓ) is a band-pass filter that transmits only the B ₀ spectral band and reflects the B _R and Anti- _Stokes Raman scattering spectral bands ^.

There figure 19 represents another case of spectral distribution of the laser excitation display bands in the case where the anti-Stokes and Stokes Raman lines are measured; this case is not part of the invention.

The B _V viewing band is here located at wavelengths lower than the Anti-Stokes Raman scattering band B _R ^aS . The configurations described in connection with the figures 20 to 23 , not forming part of the invention, make it possible to carry out measurements either of Raman Stokes lines alone or simultaneously of Raman Stokes and Anti-Stokes lines.

To the figure 20 , the filter (12m) allows the excitation laser beam (1) and the viewing beam (2) to be superimposed. The excitation beam (1) is transmitted and the viewing beam (2) is reflected by the filter (12m). On the scattered beam, the filter (12m) allows a scattered beam to be extracted in the viewing band B _v and the Raman scattering beam (3) and the Rayleigh scattering beam to be transmitted in the spectral band B ₀ . The filter (12m) is a high-pass filter with a cut-off wavelength located between the viewing band B _V and the anti-Stokes Raman scattering band. The filter (12m) transmits the signals in the bands B ₀ , B _R ^aS and possibly B _R Stokes and reflects the viewing band B _V . In the case where one wishes to measure only the anti-Stokes lines, the filter (13m) is a long-pass filter which transmits the B ₀ spectral band and reflects the anti-Stokes Raman scattering spectral band. In the case where one wishes to measure the Stokes and anti-Stokes lines simultaneously, the filter (13m) is a band-pass filter which transmits the B ₀ spectral band and reflects the Stokes and anti-Stokes Raman scattering bands.

There figure 21 represents another embodiment, not forming part of the invention, corresponding to the distribution shown schematically on the figure 19 The device comprises a filter (12n) and a filter (13n). The filter (12n) makes it possible to superimpose the excitation laser beam (1) and the viewing beam (2) by reflecting the beam (2) and transmitting the beam (1). On the collected scattering beam, the filter (12n) makes it possible to extract the beam scattered in the viewing band B _V and to transmit the beams scattered in the band B ₀ as well as in the Raman scattering band. The filter (13n) makes it possible to separate the beam scattered in the spectral band B ₀ of the excitation laser from the Raman scattering beam (3). The filter (12n) is a high-pass filter that transmits the spectral bands B ₀ and B _R ^aS (anti-Stokes Raman) and reflects the viewing spectral band B _V In the case where we want to measure only the Anti-Stokes lines, the filter (13n) is a low-pass filter that transmits the anti-Stokes scattering band B _R ^aS and reflects the spectral band B ₀ . In the case where we want to measure both the Stokes and anti-Stokes Raman lines, the filter (13n) is a band-stop filter that reflects the spectral band B ₀ and transmits the Stokes Raman scattering bands B _R and Anti-Stokes B _R ^aS .

There figure 22 represents yet another embodiment, not forming part of the invention, according to the diagram of the figure 19 in which a filter (12o) makes it possible to superimpose the excitation laser beam (1) and the illumination and display beam (2) by reflecting the laser beam (1) and transmitting the illumination and display beam (2) in the B _V spectral band. On the scattering beam, the filter (12o) transmits the beam scattered in the B _V display band and reflects the beam scattered in the Raman scattering bands and in the B ₀ Rayleigh scattering band. The filter (12o) is a low-pass filter which transmits the B _V display band and reflects the B _R Anti-Stokes scattering bands, the B ₀ band and possibly the Stokes Raman scattering band. The filter (13o) transmits the beam scattered in the Raman spectral bands and reflects the Rayleigh beam scattered in the B ₀ spectral band of the laser. In the case where only the anti-Stokes band is to be measured, the filter (13o) is a low-pass filter which transmits the anti-Stokes Raman scattering band and reflects the B ₀ spectral band. In the case where the Stokes and anti-Stokes lines are to be measured simultaneously, the filter (13o) is a band-stop filter which reflects the B ₀ spectral band and transmits the Stokes Raman scattering bands B _R and Anti-Stokes B _R ^aS .

There figure 23 describes a fourth embodiment, not forming part of the invention, in connection with the spectral distribution of the figure 19 . The filter (12p) allows the excitation laser beam (1) and the illumination and visualization beam (2) to be superimposed by reflecting the laser beam and transmitting the illumination and visualization beam in the B _V spectral band. On the collected scattered beam, the filter (12p) transmits the visualization beam (2) in the B _V spectral band and reflects the Raman scattering signals in the B _R spectral band and the beam scattered by Rayleigh scattering in the B ₀ spectral band. The filter (12p) thus allows the visualization beam (2) to be extracted. The filter (13p) allows the separation of the Rayleigh scattering beam in the B ₀ spectral band and the Raman scattering beam (3). The filter (12p) is a low-pass filter which transmits the B _V visualization band, reflects the Anti-Stokes Raman scattering band and the B ₀ spectral band. In the case where we wish to measure only the Anti-Stokes lines, the filter (13p) is a high-pass filter which transmits the spectral band B ₀ and reflects the Anti-Stokes Raman scattering band B _R ^aS In the case where we wish to measure the Stokes and anti-Stokes lines simultaneously, the filter (13p) is a band-pass filter which transmits the spectral band B ₀ and reflects the Stokes Raman scattering band B _R and anti-Stokes B _R ^aS

There figure 24 represents a fourth case, not forming part of the invention, where it is desired to measure only the scattering of the anti-Stokes Raman lines and where the B _V viewing spectral band is located above the B ₀ band of the excitation laser.

THE figures 25 to 28 represent different embodiments, not forming part of the invention, depending on the spectral distribution of the figure 24 .

On the figure 25 , a filter (13q) makes it possible to superimpose the excitation beam which is reflected by the filter (13q) and a viewing beam (2) transmitted by this filter. On the scattering beam, a filter (12q) reflects the beam scattered in the anti-Stokes Raman band and transmits the beam scattered in the viewing band and in the spectral band B ₀ . The filter (13q) makes it possible to transmit the signal scattered in the viewing band B _V and to reflect the Rayleigh scattering beam in the spectral band B ₀ . The filter (12q) is a high-pass filter having a cut-off wavelength between the Anti-Stokes Raman spectral band B _R ^aS and the spectral band B ₀ which therefore transmits the viewing spectral bands B ₀ and B _V and reflects the Anti-Stokes Raman spectral band. The (13q) filter is a long-pass or notch filter having a cutoff wavelength between the viewing band and the B ₀ band which transmits the B _V spectral band and reflects the B ₀ spectral band.

There figure 26 describes a second embodiment, not forming part of the invention, in connection with the spectral distribution of the figure 24 . The filter (13r) allows the transmitted excitation laser beam (1) to be superimposed on the illumination and display beam (2) which is reflected by the filter (13r). The filter (12r) transmits the combined excitation and display beam. On the scattered beam, the filter (12r) reflects the Anti-Stokes Raman scattering beam (3) and transmits the scattered beams in the spectral band B ₀ and in the display band B _v . The filter (13r) separates the scattered beam in the display band B _v and the scattered beam in the band B ₀ . The filter (12r) is a high-pass filter with a cut-off wavelength between the Anti-Stokes Raman scattering band and the band B ₀ . The filter (12r) therefore reflects the Anti-Stokes Raman band and transmits the spectral bands B ₀ and B _V . Filter (13r) is a low-pass or band-pass filter that transmits the spectral band B ₀ and reflects the viewing band B _V .

There figure 27 describes a third embodiment, not forming part of the invention, in connection with the spectral distribution of the figure 24 . The filter (12s) allows the reflected laser excitation beam (1) to be superimposed on the transmitted illumination and display beam (2). On the collected scattered beam, the filter (12s) transmits the scattered beam in the display band B _V and reflects the scattered beam in the spectral band B ₀ and in the anti-Stokes Raman scattering band B _R ^aS . The filter (12s) is a high-pass filter whose cut-off wavelength is located between the spectral band B ₀ and the display band B _V . The filter (13s) reflects the Raman scattering beam (3) in the Anti-Stokes scattering band B _R ^aS and transmits the Rayleigh scattering beam in the spectral band B ₀ . The filter (13s) is a high-pass or band-pass filter whose cut-off wavelength is located between the Anti-Stokes Raman scattering band and the B ₀ band so as to transmit the B ₀ band and reflect the Anti-Stokes Raman scattering band.

Finally the figure 28 describes a fourth embodiment, not forming part of the invention, in connection with the spectral distribution of the figure 24 . The filter (12t) allows the laser excitation beam (1) and the viewing beam (2) to be superimposed. On the scattered beam, the filter (12t) reflects the scattered beam in the anti-Stokes Raman scattering band and in the B ₀ spectral band and transmits the scattered beam in the B _V viewing band. The filter (13t) transmits the scattered beam in the anti-Stokes Raman scattering band and reflects the scattered beam in the B ₀ spectral band. The filter (12t) is a long-pass filter with a cut-off wavelength located between the B ₀ spectral band and the B _V viewing band. The filter (12t) therefore transmits the B _v viewing band and reflects the B ₀ spectral band as well as the anti-Stokes Raman scattering band. The filter (13t) is a low-pass or band-stop filter that transmits the anti-Stokes Raman scattering band and reflects the scattered band in the B ₀ spectral band.

We have described a number of embodiments. However, this description is not limiting and other embodiments are conceivable (other types of filters in particular than those of the examples); the invention being defined by the claims.

In particular, the various variant embodiments described in connection with the figures 2 , 6-8 , 11-18 , 20-23 and 25-28 all relate to a backscattering configuration. However, the same principle also applies to other Raman scattering configurations (forward scattering, or side scattering), in which case the means for superimposing the laser excitation beam and the illumination beam are separate from the means for filtering the scattering beam. The principle of using separate spectral ranges nevertheless applies in the same way. Those skilled in the art will therefore adapt the device and method of the invention to the different experimental Raman spectrometry configurations.

According to another particularly advantageous embodiment, the same principle is used with several excitation laser wavelengths at the same time and multi-cutoff filters to separate the different excitation spectral bands, the visualization spectral band and the Raman spectral bands associated respectively with each of the excitation laser wavelengths.

In the various cases of filters used in embodiments related to the figures 1 to 28 , a notch filter can be considered to simultaneously perform a high-pass filter function and a low-pass filter function. Therefore, it is equivalent to replacing a high-pass and low-pass filter with a notch filter.

Filters can be made using dielectric stacks or using the VBG (Volume Bragg Grating) technique.

The invention discloses a filter arrangement without moving parts which allows Raman measurement to be performed and the sample to be viewed, wherein viewing and measurement can be simultaneous.

The display device of the invention is compact and has a footprint reduced by half compared to a display system of the prior art based on a retractable optical component on the optical path.

The device and process are simple to use, as they do not require a motor or moving parts. The absence of moving parts also makes the device robust.

Finally, the device induces almost no losses on the Raman signal (extremely minimal losses of a few percent).

The extinction ratio of the filters can be chosen so that a very small part of the beam originating from the Rayleigh scattering of the excitation laser beam is transmitted towards the sample viewing system. In this way, the viewing system advantageously allows the sample and the position of the excitation laser beam on the sample to be viewed simultaneously. Since the Rayleigh scattering beam is very attenuated, it does not present any risk of saturating the viewing sensor, for example a CCD camera.

The possibility of viewing the sample at the same time as the Raman measurement is carried out makes possible operations based on the processing of the image of the sample. Thus it becomes possible to carry out an autofocus adjustment in real time on the image of the sample during the Raman measurement. Another application made possible by the invention is object tracking during the Raman measurement or image stabilization (by coupling the device of the invention to a system for moving the object or the sample holder). Other automatic applications based for example on image processing are also possible in combination with Raman measurements.

The device of the invention allows simultaneous visualization of a sample and Raman measurement of this sample without inducing high optical intensity losses. Advantageously, this device is composed of fixed elements.

Prior art devices involve either sequential viewing and measurement, or concurrent viewing and measurement, but with high optical intensity losses. A prior art device based on one or two beam splitters (of the beam splitter or beam splitter cube type) has a limited efficiency of between 6 and 25%.

The efficiency (in optical transmission) of a device of the invention composed of two filters is greater than or equal to 90%, or even 95%. The device of the invention has the advantage of considerably reducing optical losses, and of allowing the measurement of a Raman signal which is always very weak.

Claims (11)

1. An optical device for Raman spectrometry and for viewing a sample (7), said device comprising:

   - an excitation laser source (10) adapted to generate an excitation laser beam (1) having a spectral band B₀ centered about a wavelength λ₀,

   - detection means (18) adapted to detect a Raman scattering beam (3) in a spectral band consisted of a measurement band B_R ^aS of anti-Stokes lines and a measurement band B_R of Stokes lines,

   characterized in that the device comprises:

   - a viewing light source (11) adapted to generate a viewing beam (2) having spectral band Bv distinct from the spectral band B₀ of the laser and distinct from the spectral band of the Raman scattering beam (3) to be measured, wherein the wavelength λ₀ of the excitation laser source (10) is located at 473 nm, the viewing spectral band Bv of the viewing beam is located in a wavelength range above 600 nm, the spectral band B₀ of the laser, the spectral band Bv of the viewing beam and the spectral band of the Raman scattering beam being defined in wavelength in such a manner that:

   -viewing means (17) adapted to detect the collected beam (22) in the spectral band Bv,

   - optical superimposition means consisted of a first filter and/or a second filter adapted to be placed on the optical path of an excitation laser beam (1) having a spectral band B₀ centered about a wavelength λ₀ and on the optical path of a viewing beam (2) having a spectral band Bv distinct from the spectral band B₀ of the laser and distinct from the spectral band of the Raman scattering beam (3) to be measured, so as to form a combined excitation and viewing incident beam toward the sample (7);

   - an optical system adapted to direct the combined excitation and viewing incident beam toward the sample (7);

   - optical separation means adapted to be placed on the path of a collected beam coming from the scattering of the combined excitation and viewing incident beam on the sample (7), said optical separation means being consisted of:

   i. the first filter (12, 12a, 12b, ..., 12r) adapted to spatially separate said collected beam into a first and a second secondary beams, said first secondary beam comprising a spectral band chosen from the spectral band B₀ of the laser, the spectral band Bv of the viewing beam and the spectral band of the Raman scattering beam, and said second secondary beam comprising the two other remaining spectral bands among the spectral band B₀ of the laser, the spectral band Bv of the viewing beam and the spectral band of the Raman scattering beam; and

   ii. the second filter (13, 13a, 13b, ..., 13r) placed on the path of the second secondary beam and adapted to spatially separate said second secondary beam into a first and a second tertiary beams, each respectively comprising one of the two remaining spectral bands among the spectral band B₀ of the laser, the spectral band Bv of the viewing beam and the spectral band of the Raman scattering beam and

   - an optical system adapted to direct the secondary or tertiary beam (22) of spectral band Bv toward said viewing means (17); and

   - an optical system adapted to direct the secondary or tertiary Raman scattering beam (3) in the spectral band B_R toward said detection means (18).
2. The device according to claim 1 characterized in that said optical superimposition means comprise an optical filter adapted to reflect said excitation laser beam of spectral band B₀ and to transmit said viewing beam of spectral band Bv.
3. The device according to claim 1 characterized in that said optical superimposition means comprise an optical filter adapted to transmit said excitation laser beam of spectral band B₀ and to reflect said viewing beam of spectral band B_V.
4. The device according to one of claims 1 to 3 characterized in that said first filter comprises an optical filter adapted to reflect said first secondary beam and to transmit said second secondary beam.
5. The device according to one of claims 1 to 4 characterized in that said first filter comprises an optical filter adapted to transmit said first secondary beam and to reflect said second secondary beam.
6. The device according to one of claims 1 to 5 characterized in that said second filter comprises an optical filter adapted to reflect said first tertiary beam and to transmit said second tertiary beam.
7. The device according to one of claims 1 to 5 characterized in that said second filter comprises an optical filter adapted to transmit said first tertiary beam and to reflect said second tertiary beam.
8. The device according to one of claims 3 to 7 characterized in that said optical filter is chosen among a high-pass, low-pass, band-pass or notch filter.
9. The device according to one of claims 1 to 8 characterized in that it further comprises autofocus adjustment means.
10. The device according to one of claims 1 to 9 characterized in that it further comprises image stabilization means coupled to means for relative displacement of the object with respect to the laser excitation beam.
11. A method for Raman spectrometry and for viewing a sample comprising the following steps:

    - superimposing an excitation laser beam (1) having a spectral band B₀ centered about a wavelength λ₀ located at 473 nm and a viewing beam (2) having a spectral band Bv located in a wavelength range above 600 nm, the spectral band Bv of the viewing beam being distinct from λ₀ and distinct from the spectral band of the Raman beam (3) to be measured consisted of a measurement band B_R ^aS of anti-Stokes lines and a measurement band B_R of Stokes lines, so as to direct on a sample (7) a combined excitation and illumination beam;

    - collecting an optical beam scattered by said sample (7);

    - spatially and spectrally separating said collected beam into two secondary beams, the first secondary beam comprising a spectral band chosen among the spectral band B₀ of the laser, the spectral band B_V of the viewing beam and the spectral band B_R of the Raman scattering beam, and the second secondary beam comprising the two other remaining spectral bands among the spectral band B₀ of the laser, the spectral band B_V of the viewing beam and the spectral band of the Raman scattering beam, the spectral band B₀ of the laser, the spectral band B_V of the viewing beam and the spectral band of the Raman scattering beam being defined in wavelength in such a manner that:

    - spatially and spectrally separating said second secondary beam into two tertiary beams, each comprising one of the two remaining spectral bands among the spectral band B₀ of the laser, the spectral band Bv of the viewing beam and the spectral band B_R of the Raman scattering beam;

    - detecting the secondary or tertiary collected beam comprising the spectral band of the Raman scattering beam consisted of the measurement band B_R ^aS of anti-Stokes lines and the measurement band B_R of Stokes lines;

    - detecting the secondary or tertiary collected beam comprising the spectral band Bv of the viewing beam.