Laser-induced breakdown spectroscopy analysis device comprising means for protecting a gas jet

Abstract

The invention relates to a device for the elementary analysis of a sample to be examined, the device comprising: - a base (1) for supporting a sample (2) to be examined; - a system (3) for generating a laser beam (31) intended to impact the sample (2) in order to generate a plasma (P) generating an optical emission (30); - means (4) for collecting the optical emission (30); - means (5) for projecting a gas jet onto the sample (2) to be examined.

Description

Device for analysis by optical emission spectrometry on plasma produced by laser comprising means for protecting a gas jet

[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 metallic solids.

[0003] The invention can be applied in particular 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 elemental analysis of metal samples.

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

[0006] Such an analysis can be 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 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 applies in particular to the in situ control and characterization of samples of parts to be analyzed.

[0010] A method and device for elemental analysis by optical emission spectrometry on plasma produced by laser in the presence of argon is described by the patent document published under number EP 0 654 663.

[0011] Conventionally, an analysis device comprises a frame on which are mounted: - a base intended to support a sample to be studied; - a module for generating a laser beam intended to impact the sample to be studied in a direction perpendicular to the base, to generate a plasma generating an optical emission; - means for collecting the optical emission; - means for projecting a jet of gas onto the sample to be studied, comprising a needle for projecting the jet of gas.

[0012] The laser beam generated by the generation module, after shaping by the 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 and located opposite the plasma.

[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 from the plasma is carried out by the collection means.

[0015] For this purpose, the collection means include an optical fiber, one free end of which is brought as close as possible to the plasma.

[0016] Once collected, the optical emission is analyzed by determination means to which the optical fiber is connected.

[0017] The means of projecting a gas (Argon or Helium) allow a sheathing of the plasma, that is to say that they bring the properties of the gas to the laser-plasma interaction.

[0018] They also limit the fouling of the focusing lens of the optical means of focusing the laser beam, by dust produced by the plasma.

[0019] However, it was found that the gas jet, although limiting fouling on the focusing lens, produces fouling of the end of the optical fiber intended to capture the optical emission of the light radiation from the plasma.

[0020] Consequently, either regular cleaning of the optical fiber must be carried out, or this optical fiber must be kept away from the plasma, and from the dust produced by the plasma, to limit its embedding, this distance nevertheless implying a degradation in the quality of the capture of the optical emission.

[0021] Furthermore, according to a conventional implementation of the device described above, the gas projection means are configured to project a gas jet with a flow rate greater than 5 L.min -1 , and the needle has an internal diameter of around 2 mm.

[0022] This configuration involves particularly expensive gas consumption.

[0023] The invention aims in particular to overcome these drawbacks of the prior art.

[0024] More specifically, the invention aims to propose a device for elementary analysis of a sample to be studied, of the type previously described, which limits, or even eliminates, the drawbacks induced by the projection of a jet of gas onto the plasma.

[0025] The invention also aims to limit, or even eliminate, the fouling of the optical fiber by dust from the plasma.

[0026] The invention also aims to propose such an analysis device which has reduced gas consumption.

[0027] This objective, as well as others which will appear subsequently, is achieved thanks to the invention which has as its subject a device for elementary analysis of a sample to be studied, the device comprising: - a base intended to support a sample to be studied; - a system for generating a laser beam intended to impact the sample to generate a plasma generating an optical emission, the generation system being configured to focus the laser beam in a focusing zone; - means for collecting the optical emission, comprising an optical fiber with a free end extending along a first optical axis oriented towards the focusing zone, the optical emission being intended to be collected via the free end;- means for projecting a gas jet onto the sample to be studied, comprising a gas jet projection needle having a terminal portion extending along a projection axis oriented towards the focusing zone;characterized in that, according to an orthogonal projection on a plane, called the base plane, in which the base is inscribed, the part of the projection axis located on the side of the projection needle relative to the focusing zone forms an angle less than or equal to 90° with the part of the first optical axis located on the side of the optical fiber relative to the focusing zone, and in that the device comprises means for moving the sample configured to move the focusing zone on the surface of the sample, according to a displacement vector Sd forming an angle less than or equal to 90° relative to a projection vector Sp of the gas jet along the projection axis, according to an orthogonal projection on a plane in which the surface of the sample is inscribed.;

[0028] Thanks to the design of the device according to the invention, the means for projecting a jet of gas make it possible to limit, or even eliminate, the fouling of the optical fiber in addition to limiting the fouling of the focusing means.

[0029] In fact, the relative positioning of the projection needle, in relation to the optical fiber and its free end, allows the gas jet to drive the dust from the plasma in a direction opposite to that of the free end of the optical fiber in relation to the plasma.

[0030] This configuration thus makes it possible to benefit from the advantages of the gas jet, such as plasma cladding, while limiting the fouling of the focusing means and the free end of the optical fiber.

[0031] Advantageously, according to an orthogonal projection on the base plane in which the base is inscribed, the part of the projection axis located on the side of the projection needle relative to the focusing zone forms an angle of between 30° and 90° with the part of the first optical axis located on the side of the optical fiber relative to the focusing zone.

[0032] The advantages provided by the invention are then better marked.

[0033] According to a preferred design, according to an orthogonal projection on the base plane in which the base is inscribed, the part of the projection axis located on the side of the projection needle relative to the focusing zone forms an angle of 45° with the part of the first optical axis located on the side of the optical fiber relative to the focusing zone.

[0034] By means of this preferred embodiment, the advantages relating to the angle formed by the projection axis with the first optical axis are optimized, and the disadvantages minimized.

[0035] According to a preferred characteristic, on a plane, called the inclination plane, in which the projection axis is inscribed, and where the inclination plane is orthogonal to the base plane, the projection axis forms an acute angle less than or equal to 30° relative to the base plane.

[0036] In this way, the inclination of the projection needle helps to improve the advantages of the invention.

[0037] According to a preferred solution, according to an orthogonal projection on the base plane, an emerging end of the projection needle is positioned at a distance from the focusing zone which is greater than that of the free end of the optical fiber relative to the focusing zone.

[0038] The gas jet thus allows the plasma to be encompassed to improve the cladding and better remove dust that could move towards the end of the optical fiber.

[0039] According to an advantageous embodiment, the means for projecting a gas jet are configured to project the gas jet at a flow rate of less than 1 L.min-1, preferably with a flow rate of 0.5 L.min-1, and in that the projection needle has at its terminal portion an internal diameter of less than 1 mm, preferably equal to 0.5 mm.

[0040] In this way, gas savings are achieved compared to prior art techniques.

[0041] In addition, it has been found that this configuration allows for better targeting of the gas projection onto the plasma thanks to the higher speed of the gas jet. This results in better ejection of dust from the plasma, and reduced fouling of the optical fiber and focusing means.

[0042] This also allows the end of the optical fiber to be brought closer to the plasma, which improves the quality of the analysis.

[0043] The invention also relates to a method for elementary analysis of a sample to be studied, comprising: - simultaneously a step of projecting a jet of gas onto the sample to be studied, and a step of focusing a laser beam, in a focusing zone, onto said sample to be studied so as to produce a plasma on the surface of this sample, the jet of gas being projected along a projection axis oriented towards the focusing zone, the optical emission being intended to be collected via the free end; - a step of analyzing a spectrum of the optical emission emitted by the plasma using an optical fiber with a free end extending along a first optical axis oriented towards the focusing zone; - a step of determining, from this analysis of the spectrum, the elementary composition of the sample;characterized in that during the step of projecting a gas jet, and according to an orthogonal projection on a plane in which the surface of the sample is inscribed, the part of the projection axis located on the side of the projection needle relative to the focusing zone forms an angle less than or equal to 90° with the part of the first optical axis located on the side of the optical fiber relative to the focusing zone, and in that it comprises a step of modifying the position of the sample to be studied according to a displacement vector forming an angle less than or equal to 90°, preferably 0°, relative to a projection vector of the gas jet along the projection axis, according to an orthogonal projection on a plane in which the surface of the sample is inscribed.;

[0044] This process makes it possible to produce the same advantageous effects as the aforementioned device.

[0045] The step of modifying the position of the sample is carried out after an initial focusing of the laser beam and an initial projection of a gas jet, or as the laser beam is focused and the gas jet is projected.

[0046] This step allows the analysis of the sample surface to occur on a part of this surface which is not subject to dust accumulation following the projection of dust by the gas jet.

[0047] Advantageously, during the gas jet projection step, the gas jet is projected at a flow rate of less than 1 L.min -1 , preferably with a flow rate of 0.5 L.min -1 , and at a speed greater than 21 ms -1 , preferably equal to 42 ms -1 .

[0048] Gas savings are then achieved while improving the protection provided to the optical fiber and the focusing means against the risk of fouling, while allowing the optical fiber to be brought closer to the plasma generated to improve the quality of the analysis carried out.

[0049] 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:is a schematic representation of a device for elementary analysis of a sample to be studied, by optical emission spectrometry on plasma produced by laser, according to the invention;is a schematic representation, of an orthogonal projection on a base plane, of the relative positioning of a needle for projecting a jet of gas, and of an optical fiber of the device, with respect to the plasma intended to be generated by the device;is a schematic representation of an inclination plane illustrating the inclination of the needle with respect to the base plane;is a schematic representation illustrating a modification of the position of the sample during an analysis, to move a focusing zone.;

[0050] With reference to the, a device for elementary analysis of a sample 2 to be studied, according to the invention, is shown.

[0051] This device comprises a base 1 which is intended to support a sample 2 to be studied.

[0052] This base 1 has in particular an upper surface 10 on which the sample 2 rests.

[0053] Sample 2 is more specifically integrated into a sample holder allowing sample 2 to be studied to have a flat face to be studied extending parallel to the upper surface 10 of the base 1.

[0054] Preliminarily, the diagram shows an orthogonal projection of components of the device described in more detail later, and more specifically of the orientation of these components, on a plane, called base plane B, in which the base 1 is inscribed. More precisely and with reference to the, the upper surface 10 of the base 1 is inscribed in the base plane B.

[0055] The device also comprises a system 3 for generating a laser beam 31 which is intended to impact the sample 2 to generate a plasma P generating an optical emission 30.

[0056] This generation 3 system comprises a laser beam generation module 31, as well as, among other things, a laser beam focusing module 31.

[0057] The generation 3 system is configured to focus the laser beam 31 into a focusing zone 310.

[0058] More specifically, the generation system 3 is configured to emit the laser beam orthogonally to the upper surface 10 of the base 1. Thus, the laser beam 31 is emitted orthogonally to the flat face to be studied of the sample 2.

[0059] The focusing zone 310 essentially corresponds to the point of origin of generation of the plasma P.

[0060] As mentioned previously, the laser beam 31 generates a plasma P which generates an optical emission 30. This optical emission 30 corresponds to light radiation.

[0061] The device also comprises, as illustrated in the, means 4 for collecting the optical emission 30.

[0062] With reference to Figures 1 to 3, the collection means 4 comprise an optical fiber 41, with a free end 410 which extends along a first optical axis 411 oriented towards the focusing zone 310.

[0063] The optical emission 30 is thus collected via the free end 410 which is brought as close as possible to the plasma P.

[0064] The closer the free end 410 of the optical fiber 41 is to the plasma P, the better the collection of the optical emission 30, benefiting the quality of the analysis.

[0065] However, the closer the free end 410 of the optical fiber 41 is to the plasma P, the greater the risk of fouling of this free end 410 due to the dust generated by the plasma P.

[0066] With reference to figures 1 to 3, the device comprises means 5 for projecting a jet of gas onto the sample 2 to be studied.

[0067] These projection means 5 comprise a projection needle 51 of the gas jet.

[0068] This projection needle 51 has a terminal portion 510 which extends along a projection axis 511 which is oriented towards the focusing zone 310.

[0069] This projection needle 51 makes it possible to project the gas jet onto the plasma P, to improve the quality of the analysis as mentioned previously.

[0070] This gas jet thus produces a sheathing of the plasma P.

[0071] The gas jet also has the particularity of limiting the fouling of a focusing lens of the generation 3 system, but also of limiting the fouling of the free end 410 of the optical fiber 41.

[0072] Indeed, and as represented on the, according to the orthogonal projection on the base plane B, the part of the projection axis 511 located on the side of the projection needle 51 relative to the focusing zone 310 forms an angle A1 less than or equal to 90° with the part of the first optical axis 411 located on the side of the optical fiber 41 relative to the focusing zone 310.

[0073] More precisely, angle A1 is between 30° and 90°.

[0074] More precisely, angle A1 is 45°.

[0075] Referring now to the, a plane, called the inclination plane, is shown. This inclination plane illustrates the inclination of the projection needle 51 relative to the bottom plane B. This inclination plane is also shown on the by the section lines III-III merging on the projection axis 511.

[0076] Also, the projection axis 511 lies in this inclination plane, and this inclination plane extends orthogonally to the base plane B.

[0077] According to this inclination plane, the projection axis 511 forms an acute angle A3 less than or equal to 30° relative to the base plane B.

[0078] With reference to the, the projection needle 51 is substantially moved back relative to the free end 410 of the optical fiber 41.

[0079] Indeed, according to the orthogonal projection on the base plane B, an emerging end 512 of the projection needle 51 is positioned at a distance from the focusing zone 310 which is greater than that of the end 410 of the optical fiber 41 relative to the focusing zone 310.

[0080] These distances are represented on the by means of the circles R1 and R2 centered on the focusing zone 310. The free end 410 of the optical fiber 41 is positioned on the circle R1 which has a diameter d1, and an emerging end 512 of the projection needle 51 is positioned on the circle R2 which has a diameter d2.

[0081] According to this principle, the diameter d2 of the circle R2 is strictly greater than the diameter d1 of the circle R1.

[0082] To improve the quality of the projection of the gas jet while minimizing gas consumption, then the projection means 5 of a gas jet are configured to project the gas jet at a flow rate of less than 1 L.min -1 , and the projection needle 51 has at its terminal portion 510 an internal diameter less than 1 mm.

[0083] More specifically, the projection means 5 are configured to project the gas jet at a flow rate of 0.5 L.min -1, and the projection needle 51 has at its terminal portion 510 an internal diameter equal to 0.5 mm.

[0084] In this way, the gas jet is projected at a particularly high speed and at a low flow rate, which minimizes gas consumption while optimizing the effects produced by the gas on the plasma P compared to what the prior art proposes.

[0085] In fact, there is better sheathing and protection of the optical fiber against fouling.

[0086] In this way, it is also possible to improve the resolution and quality of the analysis due to the fact that the optical fiber can be approached even closer to the plasma P.

[0087] The device described above allows the performance of a method of elementary analysis of a sample to be studied which simultaneously comprises a step of projecting a jet of gas of the sample to be studied and a step of focusing a laser beam 30 in a focusing zone 310 on said sample 2 to be studied.

[0088] The focusing step makes it possible to produce a plasma P on the surface of this sample 2, and the gas jet is projected along the projection axis 511 oriented towards the focusing zone 310, this projection axis 511 corresponding to the orientation of the projection needle 51.

[0089] The method also comprises a step of analyzing the spectrum of the optical emission, corresponding to light radiation, emitted by the plasma P. This analysis step is carried out by means of the capture of this optical emission by the optical fiber 411 with the free end 410 extending along the first optical axis 411 oriented towards the focusing zone 310.

[0090] Finally, the analysis method includes a step of determining, from this analysis of the spectrum, the elemental composition of the sample.

[0091] The method, during the step of projecting a jet of gas, presents the parameters of the aforementioned device, in particular with respect to the angles adopted by the projection axis 511 relative to the first optical axis 411 and to the base plane B.

[0092] Furthermore, during the gas jet projection step, the gas jet is projected at a flow rate of less than 1 L.min -1, preferably with a flow rate of 0.5 L.min -1 , and at a speed greater than 21 meters per second, preferably equal to 42 meters per second.

[0093] As illustrated by the, the method also comprises a step of modifying the position of the sample 2 to be studied.

[0094] This modification step is carried out so as to move the focusing zone 310 onto the surface of the sample 2.

[0095] The modification of the position of the sample 2 to be studied is carried out according to a displacement vector Sd forming an angle less than or equal to 90° with respect to a projection vector Sp of the gas jet along the projection axis 511, according to an orthogonal projection on a plane in which the surface of the sample is inscribed.

[0096] As shown, a movement of the sample 2 according to the displacement vector Sd makes it possible to modify the location of the focusing zone 310 to bring it to a new position 310', according to the displacement D.

[0097] In other words, the sample 2 is moved laterally or forward according to the projection vector Sp of the gas jet during the analysis, so as to move the focusing zone 310 back onto a portion of the sample which is not covered with plasma dust ejected by the gas jet.

[0098] This step is also implemented by the device described above which comprises means for moving the sample configured to implement this modification step.

Claims

Device for elementary analysis of a sample to be studied, the device comprising: a base (1) intended to support a sample (2) to be studied; a system (3) for generating a laser beam (31) intended to impact the sample (2) to generate a plasma (P) generating an optical emission (30), the generation system (3) being configured to focus the laser beam (31) in a focusing zone (310); means (4) for collecting the optical emission (30), comprising an optical fiber (41) with a free end (410) extending along a first optical axis (411) oriented towards the focusing zone (310), the optical emission (30) being intended to be collected via the free end (410);means (5) for projecting a gas jet onto the sample (2) to be studied, comprising a projection needle (51) for the gas jet having a terminal portion (510) extending along a projection axis (511) oriented towards the focusing zone (310);characterized in that, according to an orthogonal projection on a plane, called the base plane (B), in which the base (1) is inscribed, the part of the projection axis (511) located on the side of the projection needle (51) relative to the focusing zone (310) forms an angle (A1) less than or equal to 90° with the part of the first optical axis (411) located on the side of the optical fiber (41) relative to the focusing zone (310), and in that the device comprises means for moving the sample configured to move the focusing zone (310) on the surface of the sample (2), according to a displacement vector (Sd) forming an angle less than or equal to 90° relative to a projection vector (Sp) of the gas jet along the projection axis (511), according to an orthogonal projection on a plane in which the surface of the sample is inscribed.; Device according to the preceding claim, characterized in that, according to an orthogonal projection on the base plane (B) in which the base (1) is inscribed, the part of the projection axis (511) located on the side of the projection needle (51) relative to the focusing zone (310) forms an angle (A1) of between 30° and 90° with the part of the first optical axis (411) located on the side of the optical fiber (41) relative to the focusing zone (310). Device according to the preceding claim, characterized in that, according to an orthogonal projection on the base plane (B) in which the base (1) is inscribed, the part of the projection axis (511) located on the side of the projection needle (51) relative to the focusing zone (310) forms an angle (A1) of 45° with the part of the first optical axis (411) located on the side of the optical fiber (41) relative to the focusing zone (310). Device according to any one of the preceding claims, characterized in that, on a plane, called the inclination plane, in which the projection axis (511) is inscribed, and where the inclination plane is orthogonal to the base plane (B), the projection axis (511) forms an acute angle (A3) less than or equal to 30° relative to the base plane (B). Device according to any one of the preceding claims, characterized in that, according to an orthogonal projection on the base plane (B), an emerging end (512) of the projection needle (51) is positioned at a distance from the focusing zone (310) which is greater than that of the free end (410) of the optical fiber (41) relative to the focusing zone (310). Device according to any one of the preceding claims, characterized in that the means (5) for projecting a gas jet are configured to project the gas jet at a flow rate of less than 1 L.min -1, preferably with a flow rate of 0.5 L.min -1 , and in that the projection needle (51) has at its terminal portion (510) an internal diameter less than 1 mm, preferably equal to 0.5 mm. Method for elementary analysis of a sample to be studied, comprising: - simultaneously a step of projecting a jet of gas onto the sample (2) to be studied, and a step of focusing a laser beam (31), in a focusing zone (310), onto said sample (2) to be studied so as to produce a plasma (P) on the surface of this sample, the jet of gas being projected along a projection axis (511) oriented towards the focusing zone (310); - a step of analyzing a spectrum of the optical emission emitted by the plasma using an optical fiber (41) with a free end (410) extending along a first optical axis (411) oriented towards the focusing zone (310), the optical emission (30) being intended to be collected via the free end (410); - a step of determining, from this analysis of the spectrum, the elementary composition of the sample;characterized in that during the step of projecting a gas jet, and according to an orthogonal projection on a plane in which the surface of the sample is inscribed, the part of the projection axis (511) located on the side of the projection needle (51) relative to the focusing zone (310) forms an angle (A1) less than or equal to 90° with the part of the first optical axis (411) located on the side of the optical fiber (41) relative to the focusing zone (310), and in that it comprises a step of modifying the position of the sample (2) to be studied according to a displacement vector (Sd) forming an angle less than or equal to 90°, preferably 0°, relative to a projection vector (Sp) of the gas jet along the projection axis (511), according to an orthogonal projection on a plane in which the surface of the sample (2) is inscribed.; Method according to the preceding claim, characterized in that during the step of projecting a jet of gas, the jet of gas is projected at a flow rate of less than 1 L.min -1 , preferably with a flow rate of 0.5 L.min -1 , and at a speed greater than 21 ms -1 , preferably equal to 42 ms -1 .

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