Method for mapping and analyzing at least one element of interest and associated device

Abstract

Title: Method for mapping and analyzing at least one element of interest and associated device. The invention relates to a method for mapping and analyzing at least one element of interest contained in a sample (150) by optical emission spectrometry on a laser-produced plasma (160), comprising: - a step of producing a plasma (160) by focusing a laser beam (120) onto a surface of the sample (150); - a step of collecting optical emission from the plasma (160), defining an intensity signal; - a step of processing and analyzing the optical emission; and - characterized in that, during the processing and analysis step, the intensity signal is studied over its entire duration to identify a maximum intensity value. Figure for the abstract: Fig. 2

Description

Title of the invention: Method for mapping and analyzing at least one element of interest and associated device

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

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

[0003] The invention can in particular be applied to the elemental analysis of hydrogen and oxygen by optical emission spectrometry on laser-produced plasma, 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 ability of devices used in particularly severe environments, for example in aircraft or spacecraft, it may prove essential to carry out the elemental analysis of metallic samples.

[0005] More specifically, it may be necessary to be able to map these elements within the analyzed sample. By mapping, we mean an identification of the elements composing the analyzed sample and, possibly, the distribution and the relationship between the different elements.

[0006] Such an analysis can prove particularly useful in studies of hydrogen embrittlement of metals, 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 of mapping elements present in samples.

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

[0009] This method is particularly applicable to the control and in situ characterization of samples of parts to be analyzed.

[0010] A method and device for elemental analysis by laser-produced plasma optical emission spectrometry is described in patent document published under number WO 2012 / 032024 Al, referred to as document "WO024".

[0011] Typically, such an analysis device comprises: - a laser beam generation module intended to impact a sample to be studied in order to generate a plasma producing 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 point of impact of the laser beam on the sample to be studied, the plasma generating an optical emission to be analyzed in order to map the elements composing the sample studied.

[0014] The collection of the optical emission from 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 collimating 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 specifically selected to offer the most selective "bandwidth" possible around the central wavelength of a signal of interest.

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

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

[0019] Fig. 1 schematically illustrates the evolution of the 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 intensity signal 11 is represented using a double solid line.

[0021] It is also illustrated, depending on the time: - the evolution of the intensity of a signal from the continuum 12, represented using a dotted line; - the evolution of the intensity of a signal of interest 13, represented using a single solid 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 signal from the continuum 12 integrates radiation located in the bandwidth of the interference filter selected according to the central wavelength of the signal of interest 13.

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

[0024] The signal of matrix 14 corresponds to the more general optical emission of the material in which the element to be quantified is located, this optical emission also integrating radiation located in the bandwidth of the interference filter selected according to the central wavelength of the signal of interest 13.

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

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

[0027] In order to compensate for this background noise, document WO024 proposes solutions implementing a time window for detection of determined duration whose starting time has a delay relative to the pulses of the pulsed laser adapted to the atomic line of the atomic element, and also the insufflation of a gas having the capacity to improve the signal of interest 13 with regard to other signals.

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

[0029] According to document WO024, the selection makes it possible to confer good spectral selectivity of the emission.

[0030] On the other hand, spectral analysis of the collected emission provides inaccurate results for mapping an element of interest.

[0031] Indeed, according to document WO024, the collected intensity signal 11 is used to obtain an overall value.

[0032] In other words, the overall value corresponds to the sum of the continuum signal 12, the signal of interest 13 and the matrix signal 14.

[0033] It is therefore not possible to specifically distinguish the signal of interest 13, that is to say the signal of the element of interest that we seek to analyze.

[0034] Therefore, the result of the analysis is only approximate.

[0035] Furthermore, the emission of the laser pulse can fluctuate by a few nanoseconds.

[0036] Now, by predetermining a time window on a theoretical impulse, it is It is possible that the delay is such that the time window is out of sync with the intensity signal 11.

[0037] Therefore, the collected intensity signal 11 can either be weak, or even non-existent, or be highly noisy, i.e. present too much noise compared to the signal of interest (for example too much continuum signal 12).

[0038] More specifically, spectral analysis requires a significant amount of time to obtain qualitative results.

[0039] Moreover, the definition of the time window does not guarantee a usable transmission signal for mapping.

[0040] Indeed, various parameters can influence the generation of the plasma, and thus generate the collection of an intensity signal 11 presenting a large portion of the continuum signal 12.

[0041] Such a collection then makes it difficult to study the intensity signal 11 and therefore to map the element of interest.

[0042] The invention aims in particular to overcome the disadvantages of the prior art.

[0043] More specifically, the invention aims to provide a solution enabling precise analysis of the optical emission of the plasma.

[0044] The invention also aims to provide such a solution which allows for rapid analysis of the optical emission of the plasma.

[0045] The invention further aims to provide such a simple implementation solution.

[0046] These objectives, as well as others that will appear subsequently, are achieved through the invention, which relates to a method for mapping and analyzing at least one element of interest contained in a sample by laser-produced plasma optical emission spectrometry, comprising: - a step of producing a plasma by focusing a laser beam onto a surface of the sample; - a step of collecting an optical emission from the plasma, defining an intensity signal; - a step of processing and analyzing the optical emission, and - a mapping step of at least one element of interest by sequentially renewing the production step, followed by the collection step and the processing and analysis step, in different locations on the surface of the sample, characterized in that during the processing and analysis stage, the intensity signal is studied over its entire duration to identify a maximum intensity value.

[0047] Compared to the method used in document WO024, which determines a time window for analyzing the intensity signal prior to the creation of the plasma, the method according to the invention proposes an analysis of the entire intensity signal after the generation of the plasma, in order to identify the optimal part of the signal to be exploited.

[0048] Such a process thus makes it possible to ensure that the useful part of the signal of interest, corresponding to the element of interest to be mapped, is exploited.

[0049] By "useful part" is meant a duration of the signal in which the signal of interest is sufficiently far from the continuum signal.

[0050] On the other hand, in the case of the method according to document WO024, if the window is poorly predetermined or external elements disrupt the generation of the plasma, then obtaining an accurate map of the element of interest is considerably limited.

[0051] According to an advantageous aspect, during the processing step, the intensity signal is filtered to extract a signal of interest.

[0052] The mapping of the element of interest is then more precise since, after filtering, the signal of interest can be used without being disturbed by the continuum signal.

[0053] Moreover, this makes it possible to exploit the signal of interest faster since it is free of all the noise, that is to say, the signal which does not correspond to the signal of interest, or almost.

[0054] According to another advantageous aspect, during the mapping step, only a part of the signal of interest is used.

[0055] This makes it possible to limit the analysis time to obtain an accurate map of the element of interest.

[0056] Indeed, since only a part of the signal of interest is studied, the volume of data used is small and therefore transfers quickly.

[0057] In addition, the analysis is done on a denoised signal, i.e. filtered, therefore more easily exploitable.

[0058] According to another advantageous aspect, the part of the signal of interest used corresponds to a range of the intensity signal extending over 5 to 500 nanoseconds around a point corresponding to the maximum intensity value.

[0059] Defining such a range of values ​​makes it possible to guarantee a usable signal while limiting the presence of noise, in particular formed by the continuum signal.

[0060] Furthermore, the extension of the signal around the maximum intensity value makes it possible to ensure that it is indeed the maximum intensity signal and not a disturbance in the total signal which could be confused with the maximum intensity signal.

[0061] According to another advantageous aspect, the part of the signal of interest used corresponds to a range of the signal intensity from 5 nanoseconds before the point corresponding to the maximum intensity value to 500 nanoseconds after said point corresponding to the maximum intensity value.

[0062] This choice of range makes it possible to finely limit the duration of the intensity signal to be exploited, and therefore the duration of the signal of interest.

[0063] According to another advantageous aspect, the part of the signal of interest used corresponds to a range of the intensity signal extending over 5 to 500 nanoseconds from a point corresponding to the maximum intensity value.

[0064] Other features and advantages of the invention will become more apparent at the reading the following description of a preferred embodiment of the invention, given by way of illustrative and non-limiting example, and the attached drawings described below.

[0065] [Fig. 1] The [Fig.1] is a schematic representation of the evolution of the intensity of the optical emission of a plasma as a function of time.

[0066] [Fig.2] Fig.2 is a schematic representation of a mapping device and analysis, according to the invention.

[0067] [Fig. 3] Fig. 3 is a schematic representation of a detection limit in function of time.

[0068] Figure 2 schematically illustrates a mapping and analysis device, according to the invention.

[0069] Device 100 comprises: - a 110 generation module of a 120 laser beam; - means of collecting 130 of an optical emission; - means of analyzing 140 of optical emission.

[0070] The laser beam 120 intended to impact a sample 150 to be studied in order to generate a plasma 160 producing an optical emission.

[0071] Said optical emission is then collected by the collection means 130 in order to be analyzed by the analysis means 140.

[0072] More specifically, the laser beam 120 generated by the generation module is applied to the sample 150 to be studied via optical focusing means 170 (schematically represented).

[0073] The sample 150 is placed on a mobile support 155 to move the sample 150 in order to produce plasmas in different locations of the sample 150.

[0074] The focusing means 170 include, for example, a focusing objective whose axis is perpendicular to the surface of the sample 150 to be studied.

[0075] According to the embodiment illustrated in [Fig.2], the collection means 130 comprise at least one optical fiber.

[0076] The optical fiber or fibers have a free end intended to be positioned in the immediate vicinity of the plasma 160 to capture a light intensity from the plasma 160. This light intensity then forms the intensity signal 11 illustrated by [Fig.1], which is then analyzed by the analysis means 140.

[0077] With reference to [Fig.1], a curve illustrating the evolution over time of the intensity of the intensity signal 11 collected by the collection means 130 is represented by means of a double solid line.

[0078] More specifically, the intensity signal 11 consists of at least one continuum signal 12, a signal of interest 13 and a matrix signal 14.

[0079] Figure 1 also illustrates, as a function of time: - the evolution of the intensity of a signal from the continuum 12, represented using a dotted line; - the evolution of the intensity of a signal of interest 13, represented using a single solid line; - the evolution of the intensity of a signal from matrix 14, represented using a dashed line.

[0080] 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 according to the central wavelength of the signal of interest 13.

[0081] The signal of interest 13 corresponds to the optical emission of the element that we seek to quantify, this optical emission taking place only at a discrete, and known, wavelength, a function of the quantified element.

[0082] The signal of matrix 14 corresponds to the more general optical emission of the material in which the element to be quantified is located, this optical emission also integrating radiation located in the bandwidth of the interference filter selected according to the central wavelength of the signal of interest 13.

[0083] The collected signal 11 thus corresponds to radiation captured by the collection means 130, which integrates the continuum signal 12, the signal of interest 13, as well as the matrix signal 14.

[0084] The continuum signal 12 and the matrix signal 14 thus form a particularly intense background noise with regard to the signal of interest 13.

[0085] To analyze the signal 11, the analysis means 140 include an acquisition card 141.

[0086] The acquisition card 141 is advantageously clocked at at least 200 MHz.

[0087] Preferably, the acquisition card 141 is clocked at 500 MHz.

[0088] The acquisition card 141 could even be clocked at 2GHz to provide optimal signal processing of intensity 11.

[0089] The acquisition card 141 is then used to study the intensity signal 11 over its entire duration in order to identify a maximum intensity value.

[0090] In addition, the analysis means 140 include a photomultiplier 142 for electrically creating the intensity signal 11 of the brightness of the plasma 160 collected by the optical fiber or each of the collection means 130.

[0091] The signal 11 thus amplified is then transmitted to the acquisition card 141 at the output of the photomultiplier 142.

[0092] The acquisition card 141 is then used to analyze the intensity signal 11 and, via one or more dedicated transformation laws, define a limit detection curve 15 (LDD) as illustrated by [Fig.3].

[0093] The detection limit 15 is thus inverse to the intensity signal 11.

[0094] More specifically, the detection limit 15 is inverse to the signal of interest 13.

[0095] Thus, by identifying the lowest point of the detection limit 15, it is possible to to know the moment, or almost the moment, at which the signal of interest 13 reaches its maximum value.

[0096] To enable the mapping of the sample 150, the signal 11 is then filtered by the analysis means 140 in order to extract the signal of interest 13.

[0097] Despite the filtering, it is possible that the signal used may still contain noise around the signal of interest.

[0098] To carry out the mapping of sample 150, in particular to know the concentration of an element of interest, the signal of interest is exploited only over a portion of its duration.

[0099] More specifically, thanks to the analysis of the intensity signal 11 over its entire duration, it is possible to select only a part of the intensity signal 11. Consequently, only a corresponding part of the signal of interest 13 can be used subsequently to carry out the mapping of the element of interest of the sample 150.

[0100] The used part of the intensity signal 11, and therefore of the signal of interest 13, corresponds for example to a range of the intensity signal 11 extending over 5 to 500 nanoseconds around a point corresponding to the maximum intensity value.

[0101] Alternatively, the used part of the intensity signal 11, and therefore of the signal of interest 13, corresponds for example to a range of the intensity signal 11 going from 5 nanoseconds before the point corresponding to the maximum intensity value to 500 nanoseconds after said point corresponding to the maximum intensity value.

[0102] According to yet another variant, the used part of the intensity signal 11, and therefore of the signal of interest 13, corresponds to a range of the intensity signal extending from 5 to 500 nanoseconds from the point corresponding to the maximum intensity value.

[0103] This allows the signal of interest to be studied over a period allowing precise results to be obtained quickly for mapping the element of interest.

[0104] The mapping of the element of interest is thus carried out according to a mapping and analysis process of at least one element of interest included in a sample 150 by optical emission spectrometry on laser-produced plasma 160, comprising: - a plasma production step 160 by focusing the laser beam 120 onto a surface of the sample 150; - a step of collecting the optical emission from the plasma 160, defining the intensity signal 11; - a step of processing and analyzing the optical emission, and - a mapping step of at least one element of interest by renewal quantity of the production stage, followed by the collection stage and the processing and analysis stage, in different locations on the surface of the sample 150.

[0105] Compared to the method used in document WO024, which determines a time window for analyzing the intensity signal prior to the creation of the plasma 160, the method according to the invention proposes an analysis of the entire intensity signal 11 after the generation of the plasma 160, in order to identify only a part to be exploited.

[0106] This makes it possible to ensure that the useful part of the signal of interest 13 is usable.

[0107] By "useful part" is meant a duration of the signal in which the signal of interest 13 is sufficiently far from the continuum signal 12 and the matrix signal 14.

[0108] The mapping of the element of interest is then more precise since, after filtering, the signal of interest can be used without being disturbed by the signal of the continuum 12 or that of the matrix.

[0109] On the other hand, in the case of the method according to document WO024, if the window is poorly predetermined or external elements disturb the generation of the plasma 160, then the intensity signal 11 has a high risk of including part of the continuum signal 12, thus limiting the obtaining of an accurate map of the element of interest.

[0110] The filtering of the signal of interest 13 can be carried out using a second signal collected simultaneously with the signal of interest 11.

[0111] More specifically, the signal of interest 11 is denoised using the second signal.

[0112] Thus, the signal of interest 13 can be obtained by subtracting the second signal from the first signal of intensity 11.

[0113] For this purpose, the method may include a preliminary calibration step during which a curve of evolution of an intensity of the signal of intensity 11 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.

[0114] The second signal is also obtained by the collection means 130 which then include a secondary optical fiber dedicated to the acquisition of the second signal.

Claims

Demands

1. A method for mapping and analyzing at least one element of interest contained in a sample (150) by optical emission spectrometry on laser-produced plasma (160), comprising: - a step of producing a plasma (160) by focusing a laser beam (120) onto a surface of the sample (150); - a step of collecting an optical emission from the plasma (160), defining an intensity signal (11); - a step of processing and analyzing the optical emission; and - a step of mapping at least one element of interest by sequentially repeating the production step, followed by the collection step and the processing and analysis step, at different locations on the surface of the sample (150), characterized in that during the processing and analysis step, the intensity signal (11) is studied over its entire duration to identify a maximum intensity value.

2. A method according to claim 1, characterized in that during the processing step, the intensity signal (11) is filtered to extract a signal of interest (13).

3. Method according to the preceding claim, characterized in that during the mapping step, only a part of the signal of interest (13) is used.

4. A method according to the preceding claim, characterized in that the portion of the signal of interest (13) used corresponds to a range of the intensity signal (11) extending over 5 to 500 nanoseconds around a point corresponding to the maximum intensity value.

5. A method according to the preceding claim, characterized in that the portion of the signal of interest (13) used corresponds to a range of the intensity signal (11) from 5 nanoseconds before the point corresponding to the maximum intensity value to 500 nanoseconds after said point corresponding to the maximum intensity value.

6. A method according to any one of claims 1 to 3, characterized in that the portion of the signal of interest (13) used corresponds to a range of the intensity signal (11) extending over 5 to 500 nanoseconds from a point corresponding to the maximum intensity value.

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