Method and device for mapping and analysis by laser-produced plasma optical emission spectrometry

Abstract

Title: Method and Device for Mapping and Analysis by Laser Plasma Optical Emission Spectrometry. The invention relates to a method for mapping and analyzing at least one element of interest contained in a sample (2) by laser plasma optical emission spectrometry, comprising: - a step of producing a plasma (P) by focusing a laser beam (31) onto the surface of the sample (2); - a step of collecting optical emission from the radiation (30) of the plasma (P), during which a first signal (S1) is collected by filtering the optical emission to a wavelength corresponding to the atomic line of the element of interest, called the "wavelength of interest," or to a narrow range of wavelengths surrounding the wavelength of interest; - a step of processing and analyzing the optical emission to map the element of interest in the sample (2). Figure for the abstract: Fig. 2

Description

Title of the invention: Method and device for mapping and analysis by optical emission spectrometry on plasma produced by laser

[0001] The present invention relates to the field of high-resolution mapping and analysis of elements in solids.

[0002] More particularly, the invention relates, in particular but not exclusively, to a high-resolution analysis device for mapping elements in samples.

[0003] The invention can in particular be applied to the elemental analysis of hydrogen and oxygen by optical emission spectrometry on plasma produced by laser, in the field of the nuclear industry, or even the aeronautical or space industry.

[0004] In applications such as the characterization of devices subjected to radioactive sources, or the characterization of the aging capacity of devices used in particularly harsh environments, for example in aircraft or spacecraft, it may prove essential to carry out the elementary analysis of metal samples.

[0005] More specifically, it may be necessary to be able to draw up a map of these elements within the analyzed sample. By map is meant an identification of the elements making up the analyzed sample and, possibly, the distribution and the link between the different elements.

[0006] Such an analysis may prove particularly useful in studies of metal embrittlement by hydrogen, or in studies of aging of fuel cladding in the presence of oxygen, or in studies of embrittlement of fuel cladding caused by the formation of hydrides, the latter promoting the propagation of cracks.

[0007] There are various known methods for mapping elements present in samples.

[0008] One of these methods is elemental analysis by optical emission spectrometry on plasma produced by laser, designated by the acronym "SEOPPL", a technique which is practiced in a natural atmosphere, also designated by the English acronym "LIBS" corresponding to the English expression "laser induced breakdown spectroscopy".

[0009] This method applies in particular to the in situ control and characterization of samples of parts to be analyzed.

[0010] A method and device for elementary analysis by optical emission spectrometry on plasma produced by laser is described by the patent document published under the number WO 2012 / 032024 Al, known as document “WO024”.

[0011] Conventionally, such an analysis device comprises: - a module for generating a laser beam intended to impact a sample to be studied to generate a plasma generating an optical emission; - means of collecting optical emission; - means of analyzing optical emission.

[0012] The laser beam generated by the generation module, after shaping by a shaping module, is applied to a sample to be studied via optical focusing means, comprising a focusing objective whose axis is perpendicular to the surface of the sample.

[0013] A plasma is then created at the impact of the laser beam on the sample to be studied, the plasma generating an optical emission to be analyzed to map the elements making up the sample studied.

[0014] The collection of the optical emission of the plasma is carried out by the collection means. These collection means comprise an optical fiber, one free end of which is brought as close as possible to the plasma.

[0015] The solution proposed by document WO024 implements an interference filter positioned between a collimation lens and a photomultiplier.

[0016] The light captured by the optical fiber is collimated by the collimating lens and the resulting light beam passes through the interference filter and illuminates the photomultiplier. This interference filter allows only a predetermined range of wavelengths to pass through, and is notably selected to offer the most selective possible “passband” around the central wavelength of a signal of interest.

[0017] Once collected, the optical emission, and more specifically the intensity of this optical emission, are analyzed by the analysis means.

[0018] One problem lies in the nature of the optical emission collected.

[0019] [Fig.l] schematically illustrates the evolution of an intensity of the optical emission collected by the collection means as a function of time.

[0020] A curve illustrating the evolution over time of the intensity of a collected signal 11 is represented using a double continuous line.

[0021] It is also illustrated, as a function of time: - the evolution of the intensity of a signal from continuum 12, represented using a dotted line; - the evolution of the intensity of a signal of interest 13, represented using a single continuous line; - the evolution of the intensity of a signal from matrix 14, represented using a dashed line.

[0022] The continuum signal 12 corresponds to the optical emission of the plasma. This continuum signal 12 integrates radiation located in the bandwidth of the interference filter selected as a function of the central wavelength of the signal of interest 13.

[0023] The signal of interest 13 corresponds to the optical emission of the element that one seeks to quantify, this optical emission only taking place at a discrete, and known, wavelength, which is a function of the quantified element.

[0024] The signal from matrix 14 corresponds to the more general optical emission of the material in which the element that one seeks to quantify is located, this optical emission also integrating radiation located in the passband of the interference filter selected as a function of the central wavelength of the signal of interest 13.

[0025] The collected signal 11 thus corresponds to radiation captured by the collection means which integrates the signal from the continuum 12, the signal of interest 13, as well as the signal from the matrix 14.

[0026] The signal from the continuum 12 and the signal from the matrix 14 then form a particularly intense background noise with respect to the signal of interest 13.

[0027] In order to compensate for this background noise, document WO024 proposes solutions implementing a detection time window centered on the signal of interest 13, and also the insufflation of a gas having the capacity to improve the signal of interest 13 with respect to the other signals.

[0028] In practice, these solutions are not entirely satisfactory.

[0029] The invention aims in particular to propose an alternative or complementary technique aimed at improving the quantification of an element of interest compared to the technique described in document WO024.

[0030] The invention also aims to provide such a quantization technique which takes into account the background noise from the continuum and the matrix.

[0031] These objectives, as well as others which will appear subsequently, are achieved thanks to the invention which has as its subject a method of mapping and analyzing at least one element of interest included in a sample by optical emission spectrometry on plasma produced by laser, comprising: - a step of producing a plasma by focusing a laser beam on the surface of the sample; - a step of collecting an optical emission from the radiation of the plasma, during which a first signal is collected by filtering the optical emission at a wavelength corresponding to the atomic line of the element of interest, called the “wavelength of interest”, or to a narrow range of wavelengths surrounding the wavelength of interest; - a step of processing and analysis of the optical emission to map the element of interest in the sample; characterized in that in the collecting step, a second signal is collected by filtering the optical emission at a wavelength, or a narrow range of wavelengths, adjacent to the wavelength of interest, and in that during the processing and analysis step, a signal of interest is obtained by denoising the first signal using the second signal.

[0032] The second collected signal is obtained by filtering the optical emission at a wavelength or narrow range adjacent to the wavelength of interest. Since the element of interest being mapped emits radiation only at a specific wavelength corresponding to the atomic line of the element of interest, then the intensity of the second signal results only from the continuum and the matrix. The second signal can be likened to background noise.

[0033] Unlike the second signal, the first signal also integrates the radiation of the element of interest which is at the wavelength of interest. Consequently, the second signal can be assimilated to the background noise of the first signal with respect to the signal of interest, of course subject to a variation due to the shift in the capture wavelengths between the first signal and the second signal.

[0034] The signal of interest obtained thus corresponds to the signal of interest without the background noise resulting from the continuum signal and the matrix signal.

[0035] The method according to the invention thus makes it possible to improve the quantification of an element of interest compared to the techniques of the prior art.

[0036] According to a preferred variant, during the processing and analysis step, the signal of interest is obtained by subtracting the second signal from the first signal.

[0037] This variant makes it possible to denoise the signal of interest in a particularly simple manner.

[0038] According to an advantageous solution, during the processing and analysis step, a total intensity of the signal of interest is determined by calculating the integral of the evolution of the intensity of the signal of interest as a function of time.

[0039] The total intensity of the signal of interest thus only includes the signal of interest, and not a signal of interest added to noise resulting from the continuum signal and the matrix signal.

[0040] According to a preferred embodiment, the method comprises a preliminary calibration step during which a curve of evolution of an intensity of a signal of interest as a function of a concentration of the element of interest is defined using a plurality of standards each comprising a known concentration of the element of interest.

[0041] The method thus has a measurement sensitivity much greater than that permitted by the methods according to the prior art.

[0042] According to an advantageous solution, during the processing and analysis step, the total intensity of the signal of interest of the sample is reported on the evolution curve for obtain a concentration of the element of interest in the sample.

[0043] The concentration of the element of interest obtained in the sample, thanks to the method, is much more precise and sensitive than that which can be obtained by methods according to the prior art.

[0044] According to a preferred variant, to obtain the second signal, the optical emission is filtered at a wavelength or at a narrow range of wavelengths directly adjacent to the wavelength of interest.

[0045] By the expression "directly adjacent" it is understood that the filtering wavelength, or the end of the narrow range of filtering wavelengths, is less than 1.5 nm from the wavelength of interest.

[0046] According to another preferred variant, to obtain the second signal, the optical emission is filtered at a wavelength or at a narrow range of wavelengths shifted by less than 100 nm, advantageously shifted by less than 10 nm, typically shifted by 1.5 nm, from the wavelength of interest.

[0047] According to an advantageous characteristic, to obtain the second signal, the narrow range of wavelengths of the optical emission has a width identical to the width of the narrow range of wavelengths of the first signal.

[0048] Thanks to these identical widths, the quantities of photons collected for the two signals are comparable, and it is thus avoided to add additional “noise” (counting noise) to the intrinsic noise present during the measurements.

[0049] The narrow wavelength range of the first signal and / or the second signal are in particular 1 nm or less than 1 nm wide.

[0050] Preferably, during the collection step, the second signal is collected simultaneously with the first signal.

[0051] The invention also relates to a device for mapping and analyzing at least one element of interest included in a sample by optical emission spectrometry on plasma produced by laser, comprising: - a module for generating a laser beam on the sample; - a system for collecting an optical emission from radiation from a plasma produced by focusing the laser beam on the sample, the collection system comprising a first collection path comprising first filtering means filtering the optical emission at a wavelength corresponding to the atomic line of the element of interest, called the “wavelength of interest”, or to a narrow range of wavelengths surrounding the wavelength of interest; - an optical emission processing and analysis system to map the element of interest in the sample; characterized in that the collection system comprises a second collection path comprising second filtering means filtering the optical emission at a wavelength wavelength, or a narrow range of wavelengths, adjacent to the wavelength of interest, and in that the processing and analysis system comprises means for denoising a first signal from the first channel using a second signal from the second channel, preferably obtained synchronously when obtaining the first signal, to obtain a signal of interest.

[0052] This device has the same advantages as those of the aforementioned method according to the invention.

[0053] The first filtering means and / or the second filtering means may correspond, for example, to interference filters and / or monochromators.

[0054] Obtaining the two signals synchronously makes it possible to avoid any variation in the intrinsic “noise” level between the first signal and the second signal.

[0055] Preferably, the first filtering means and the second filtering means are formed respectively by a first interference filter and by a second interference filter.

[0056] Other characteristics and advantages of the invention will appear more clearly on reading the following description of different preferred embodiments of the invention, given as illustrative and non-limiting examples, and the appended drawings among which: • [Fig.l] [Fig.l] schematically illustrates, in the context of optical emission spectrometry on plasma produced by laser, the evolution of an intensity of the optical emission collected as a function of time, as well as the components of this optical emission which are the continuum signal, the signal of interest, and the matrix signal; • [Fig.2] [Fig.2] schematically illustrates the superimposed curves of the evolution of the intensity as a function of time of a first signal and a second signal collected within the framework of a method and a device, according to the invention, for mapping and analyzing an element of interest; • [Fig.3] [Fig.3] schematically illustrates the difference in intensity between the first signal and the second signal at a given time; • [Fig.4] [Fig.4] schematically illustrates an evolution curve of a intensity of a signal of interest as a function of a concentration of an element of interest; • [Fig.5] [Fig.5] is a schematic representation of a car device tography and analysis of an element of interest, according to the invention.

[0057] With reference to [Fig.5], a device, according to the invention, for mapping and analysis is described below.

[0058] This device is designed to enable mapping and analysis of at least one element of interest of a sample 2 by optical emission spectrometry on laser-produced plasma.

[0059] The device comprises: - a generation module 3 of a laser beam 31 on sample 2; - a system 4 for collecting an optical emission from radiation 30 of a plasma P produced by focusing the laser beam 31 on the sample 2; - a system for processing and analyzing 5 the optical emission to map the element of interest in the sample 2.

[0060] The collection system 4 comprises a first path for collecting the optical emission.

[0061] This first collection path comprises an optical fiber, called first optical fiber 412, intended to collect and convey the optical emission. The first optical fiber 412 thus comprises a collection end, called first collection end 413 oriented towards the plasma P.

[0062] The first collection path also comprises a photomultiplier, called first photomultiplier 414 intended to convert the optical emission into an electrical signal.

[0063] The first collection path also comprises first filtering means 411.

[0064] These first filtering means 411 are notably designed, as detailed below in relation to the method, to filter the optical emission at a wavelength corresponding to the atomic line of the element of interest, called the “wavelength of interest”, or to a narrow range of wavelengths surrounding the wavelength of interest.

[0065] In other words, the filtering means 411 block the part of the optical spectrum of the optical emission which does not correspond to the wavelength of interest or to the narrow range of wavelengths surrounding the wavelength of interest, while they allow the part of the spectrum corresponding to the wavelength of interest or to the narrow range of wavelengths surrounding the wavelength of interest to pass.

[0066] According to one possible embodiment, the first filtering means 411 can be formed by a monochromator, called the first monochromator.

[0067] Preferably, the first filtering means 411 are formed by an interference filter, called the first interference filter.

[0068] The first channel makes it possible to obtain a first signal SI resulting, among other things, from the filtering of the optical emission by the first filtering means 411.

[0069] The collection system 4 also comprises a second path for collecting the optical emission.

[0070] This second collection route is distinct from the first collection route.

[0071] This second collection path comprises an optical fiber, called the second fiber optical fiber 422, intended to collect and convey the optical emission. The second fiber optical 422 thus comprises a collection end, called second collection end 423 oriented towards the plasma P.

[0072] The second collection path also comprises a photomultiplier, called second photomultiplier 424 intended to convert the optical emission into an electrical signal.

[0073] The second collection path further comprises second filtering means 421.

[0074] These second filtering means 421 are notably designed, as detailed subsequently in connection with the method, to filter the optical emission at a wavelength, or a narrow range of wavelengths, adjacent to the wavelength of interest.

[0075] The second channel makes it possible to obtain a second signal S2 resulting, among other things, from the filtering of the optical emission by the second filtering means 421.

[0076] The processing and analysis system 5 corresponds to an electronic unit comprising, among other things, at least one processor, at least one electronic memory, and display means.

[0077] The processing and analysis system 5 also comprises means for denoising the first signal SI from the first channel using the second signal S2 from the second channel to obtain a signal of interest 13.

[0078] These noise reduction means can advantageously be formed by a parameterization of the electronic unit.

[0079] The method, according to the invention, for mapping and analyzing at least one element of interest included in a sample 2 by optical emission spectrometry on plasma produced by laser is now described.

[0080] This method, and all or part of its steps, are implemented by the device.

[0081] The method comprises a step of producing a plasma P by focusing a laser beam 31 on the surface of sample 2.

[0082] This step is implemented by the generation module 3 of a laser beam 31.

[0083] The method also comprises a step of collecting an optical emission from of 30 radiation from plasma P.

[0084] This collection step is implemented by the collection system 4.

[0085] During this collection step, the following is collected: - a first SI signal, and - a second signal S2.

[0086] The first signal SI is distinct from the second signal S2.

[0087] Advantageously, the first signal SI and the second signal S2 are collected simultaneously.

[0088] This first signal SI and this second signal S2 are collected for the analysis and mapping of the element of interest sought.

[0089] According to one possible embodiment, a mapping of several elements of interest could be carried out. In this case, for each element of interest a first signal and a second signal would be collected, distinct from the first signal and the second signal collected for each of the other elements of interest.

[0090] The first signal SI is collected by filtering the optical emission: - either at a wavelength corresponding to the atomic line of the element of interest, called the “wavelength of interest”; - either to a narrow range of wavelengths surrounding the wavelength of interest.

[0091] For example, in the case where the element of interest is hydrogen, then only the part of the optical emission which is: - either at the wavelength of 656.2 nm (wavelength of interest); - either to a narrow range surrounding this wavelength of interest.

[0092] By narrow range, it is understood a range less than or equal to 1 nm in width, and preferably at mid-height, i.e. a range whose limits are 0.5 nm from the wavelength of interest, or less than 0.5 nm from the wavelength of interest.

[0093] The second signal S2 is collected by filtering the optical emission: - either at a wavelength adjacent to the wavelength of interest; - either to a narrow range of wavelengths adjacent to the wavelength of interest.

[0094] According to an embodiment envisaged, to obtain the second signal S2, the optical emission is filtered either at a wavelength or at a narrow range of wavelengths directly adjacent to the wavelength of interest, i.e. with a difference of less than 1.5 nm.

[0095] According to a first example, still in the case where the element of interest is hydrogen and where the wavelength of interest is 656.2 nm, then the optical emission can be filtered at 657.2 nm to obtain the second signal S2.

[0096] According to another embodiment envisaged, to obtain the second signal S2, the optical emission is filtered at a wavelength or at a narrow range of wavelengths, shifted by less than 100 nm, advantageously by less than 10 nm, and typically by 1.5 nm, from the wavelength of interest.

[0097] According to a second example, still in the case where the element of interest is hydrogen and where the wavelength of interest is 656.2 nm, then the optical emission can be filtered at 666.2 nm to obtain the second signal S2.

[0098] According to a variant envisaged, to obtain the second signal S2, the narrow range of wavelengths of the optical emission has a width of 1 nm.

[0099] The width of the narrow range of wavelengths at which the optical emission is filtered to obtain the second signal is advantageously identical to the width of the narrow range of wavelengths of the first signal. This width of the range narrow wavelength range for the second signal can thus be 1 nm, or less than 1 nm.

[0100] [Fig.2] illustrates the superimposed curves of the evolution of the intensity as a function of time of the first signal SI and the second signal S2 which are collected.

[0101] As can be seen in this figure, the second signal S2 is superimposed on the first signal SI during a first phase PI and a third phase P3. However, during a second phase P2, interposed between the first phase PI and the third phase P3, the second signal S2 has an offset relative to the first signal SI.

[0102] The offset between the first signal SI and the second signal S2 results from the difference in filtering carried out during the collection of these signals.

[0103] The first signal SI corresponds to the collected signal 11 of [Fig.l], and thus integrates the continuum signal 12, the signal of interest 13, as well as the matrix signal 14.

[0104] The second signal S2 integrates only the signal from the continuum 12, as well as the signal from the matrix 14.

[0105] [Fig.3] illustrates the difference in intensity between the first signal SI and the second signal S2 at a given time during the second phase P2.

[0106] The method further comprises a step of processing and analyzing the optical emission to map the element of interest in the sample 2.

[0107] This step is implemented by processing and analysis system 5.

[0108] During this processing and analysis step, a signal of interest 13 is obtained in denoising the first signal SI using the second signal S2.

[0109] According to a first approach, during the processing and analysis step, the signal of interest 13 is obtained by subtracting the second signal S2 from the first signal SL

[0110] The method thus makes it possible to obtain the only signal of interest 13 of the element of interest, isolated from the background noise formed by the signal of the continuum 12, as well as from the signal of the matrix 14.

[0111] Then, during the processing and analysis step, a total intensity IT of the signal of interest 13 is determined by calculating the integral of the evolution of the intensity I of the signal of interest 13 as a function of time T.

[0112] In other words, the total intensity of the signal of interest 13 is determined by calculating the integral of the difference of the first signal S1 with respect to the second signal S2.

[0113] According to a first variant, the total intensity of the signal of interest 13 is determined throughout the duration of the collection of the optical emission.

[0114] According to another variant, the total intensity of the signal of interest 13 is determined for only part of the collection duration.

[0115] With reference to [Fig.4], during the processing and analysis step, the total intensity IT of the signal of interest 13 of sample 2 is plotted on a curve showing the evolution of an intensity I as a function of a concentration C, to obtain a concentration CEi of the element of interest in sample 2.

[0116] According to one embodiment envisaged, the evolution curve of [Fig.4] is a curve, fixed, predetermined and integrated into the processing and analysis system 5.

[0117] According to an advantageous embodiment, the method comprises a preliminary calibration step during which the curve of evolution of the intensity I of a signal of interest 13 as a function of a concentration C of the element of interest is defined.

[0118] During this preliminary calibration step, a plurality of standards are used, each comprising a known concentration Co, Ch C2, C3, C4 of the element of interest.

[0119] For example, it can be used: - a basic standard with a zero Co concentration in elements of interest; - a first standard with a concentration Ci, equal to 250 ppm; - a second standard with a C2 concentration equal to 500 ppm; - a third standard with a C3 concentration equal to 750 ppm; - a fourth standard with a C4 concentration equal to 1000 ppm.

[0120] For each of these standards, a first signal SI and a second signal S2 are collected, making it possible, in the manner previously described, to obtain a signal of interest, and more precisely an intensity Io, L, L, I3, L, of these signals of interest.

[0121] By plotting on a graph the intensity Io, L, F. I3,14 of these signals of interest in relation to their known concentrations Co, Ci, C2, C3, C4, a straight line is obtained making it possible to precisely determine the concentration of an element of interest included in the sample 2 analyzed.

[0122] During the method, a plurality of measurements are carried out at different locations in the sample to enable the different concentrations of elements of interest to be mapped on a given surface of the sample.

[0123] The method and device according to the invention have much better sensitivity than the methods and devices according to the prior art which do not seek to denoise the collected signal in order to only have to analyze the signal of interest.

Claims

Claims

1. Method for mapping and analyzing at least one element of interest included in a sample (2) by laser-produced plasma optical emission spectrometry, comprising: - a step of producing a plasma (P) by focusing a laser beam (31) onto the surface of the sample (2); - a step of collecting an optical emission from the radiation (30) of the plasma (P), during which a first signal (SI) is collected by filtering the optical emission at a wavelength corresponding to the atomic line of the element of interest, called the "wavelength of interest", or to a narrow range of wavelengths surrounding the wavelength of interest; - a step of processing and analyzing the optical emission to map the element of interest in the sample (2);characterized in that during the collecting step, a second signal (S2) is collected by filtering the optical emission at a wavelength, or a narrow range of wavelengths, adjacent to the wavelength of interest, and in that during the processing and analyzing step, a signal of interest (13) is obtained by denoising the first signal (SI) using the second signal (S2).;

2. Method according to the preceding claim, characterized in that, during the processing and analysis step, the signal of interest (13) is obtained by subtracting the second signal (S2) from the first signal (SI).

3. Method according to any one of the preceding claims, characterized in that, during the processing and analysis step, a total intensity (IT) of the signal of interest (13) is determined by calculating the integral of the evolution of the intensity (I) of the signal of interest (13) as a function of time (T).

4. Method according to any one of the preceding claims, characterized in that it comprises a preliminary calibration step during which a curve of evolution of an intensity (I) of a signal of interest (13) as a function of a concentration (C) of the element of interest is defined using a plurality of standards each comprising a known concentration (Co, Ci, C2, C3, C4) of the element of interest.

5. Method according to claims 3 and 4, characterized in that during the processing and analysis step, the total intensity (IT) of the signal of interest of the sample is reported on the evolution curve to obtain a concentration (CE1) of the element of interest in the sample (2).

6. A method according to any one of the preceding claims, characterized in that to obtain the second signal (S2), the optical emission is filtered at a wavelength or a narrow range of wavelengths directly adjacent to the wavelength of interest.

7. Method according to any one of claims 1 to 5, characterized in that to obtain the second signal (S2), the optical emission is filtered at a wavelength or at a narrow range of wavelengths shifted by less than 100 nm, advantageously shifted by less than 10 nm, typically shifted by 1.5 nm, from the wavelength of interest.

8. Method according to any one of the preceding claims, characterized in that to obtain the second signal (S2), the narrow wavelength range of the optical emission has a width identical to the width of the narrow wavelength range of the first signal (SI).

9. Method according to any one of the preceding claims, characterized in that during the collection step, the second signal (S2) is collected simultaneously with the first signal (SI).

10. Device for mapping and analyzing at least one element of interest (El) included in a sample (2) by optical emission spectrometry on plasma produced by laser, comprising: - a module (3) for generating a laser beam (31) on the sample (2); - a system (4) for collecting an optical emission from radiation (30) of a plasma (P) produced by focusing the laser beam (31) on the sample (2), the collection system (4) comprising a first collection path comprising first filtering means (411) filtering the optical emission at a wavelength corresponding to the atomic line of the element of interest, called the "wavelength of interest", or to a narrow range of wavelengths surrounding the wavelength of interest; - a system (5) for processing and analyzing the optical emission to map the element of interest in the sample (2);characterized in that the collection system (4) comprises a second collection path comprising second filtering means (421) filtering the optical emission at a wavelength, or at a narrow range of wavelengths, adjacent to the wavelength of interest; and in that the processing and analysis system (5) comprises means for denoising a first signal (SI) from the first channel using a second signal (S2) from the second channel, preferably obtained synchronously when obtaining the first signal, to obtain a signal of interest (13).

11. Device according to the preceding claim, characterized in that the first filtering means (421) and the second filtering means (421) are formed respectively by a first interference filter and by a second interference filter.

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