Laser-induced breakdown spectroscopy analyzer with means for protecting the gas jet - Patents.com

Abstract

The invention relates to an apparatus for the elemental analysis of a sample to be examined, comprising a base 1 for supporting the sample 2 to be examined, a system 3 for generating a laser beam 31 intended to impinge on the sample 2 in order to generate a plasma P which generates an optical emission 30, means 4 for collecting the optical emission 30, and means 5 for injecting a gas jet onto the sample 2 to be examined.

Description

[Technical Field]

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

[0002] More particularly, the present invention relates to high resolution analytical instruments, particularly but not exclusively for mapping elements within metallic solids.

[0003] The invention is particularly applicable to the elemental analysis of hydrogen and oxygen by optical emission spectroscopy on laser-produced plasmas in the field of the nuclear industry or in the aeronautical or space industry. [Background technology]

[0004] Elemental analysis of metal samples can be essential in applications such as characterizing equipment exposed to radioactive sources or characterizing the aging capabilities of equipment used in particularly harsh environments, such as aircraft or spacecraft.

[0005] More specifically, it may be necessary to be able to map these elements in the sample being analyzed, where mapping means identifying the elements that make up the sample being analyzed and, optionally, the distribution of the various elements and the chemical bonds between them.

[0006] Such analyses can be particularly useful in studying metal embrittlement by hydrogen, or fuel cladding aging in the presence of oxygen, or fuel cladding embrittlement caused by the formation of hydride compounds, which promote crack propagation.

[0007] There are a variety of known methods for mapping the elements present in a sample.

[0008] One of these methods is elemental analysis by optical emission spectroscopy on laser-produced plasma, a technique performed in natural air, also referred to by the English acronym "LIBS," which stands for "laser induced breakdown spectroscopy."

[0009] The method is particularly applicable to the in situ examination and characterization of samples of analyte moieties.

[0010] A method and apparatus for elemental analysis by optical emission spectroscopy on laser-produced plasma in the presence of argon is described in US Pat. No. 5,649,999.

[0011] Conventionally, analytical devices have - a base intended to support the sample under consideration; a module for generating a laser beam intended to impinge on the sample under consideration in a direction perpendicular to its base and to generate a plasma that generates light emission; - means for collecting luminescence; - means for injecting a gas jet into the sample under study, comprising a needle for injecting a gas jet; The device has a frame to which the

[0012] The laser beam generated by the generating module is shaped by the shaping module and then applied to the sample under study through optical focusing means comprising a focusing lens, the focusing lens having its axis perpendicular to the surface and positioned facing the plasma.

[0013] A plasma is then generated when the laser beam strikes the sample under study, which produces an optical emission that is analyzed to map the elements that make up the sample under study.

[0014] Collection of the plasma's emitted light is performed by a collection means.

[0015] For this purpose, the collecting means comprises an optical fiber whose free end is positioned as close as possible to the plasma.

[0016] The emitted light is collected and analyzed by a determination means connected to an optical fiber.

[0017] By means of gas (argon or helium) injection, a plasma sheath is possible, i.e., by means of which the properties of the gas are brought into the laser-plasma interaction.

[0018] This measure also limits the build-up of the focusing lens of the optical means for focusing the laser beam by dust generated by the plasma.

[0019] However, although the gas jet limits deposits on the focusing lens, it has been found to produce deposits on the ends of optical fibers intended to capture the emission of optical radiation from the plasma.

[0020] As a result, the optical fiber must either be periodically cleaned or be moved away from the plasma and the dust generated by the plasma to limit its deposition, which in the latter case results in a degradation of the quality of the emitted light capture.

[0021] Moreover, according to the conventional embodiment of the above-mentioned device, the means for injecting gas has a flow rate of 5 L min -1 The gas jet is configured to be injected at a flow rate greater than 1000 psi using a needle having an inner diameter of approximately 2 mm.

[0022] This configuration results in high gas consumption costs in particular. [Prior art documents] [Patent documents]

[0023] [Patent Document 1] European Patent No. 0,654,663 Summary of the Invention [Problem to be solved by the invention]

[0024] In particular, it is an object of the present invention to overcome the drawbacks of the prior art.

[0025] More particularly, the invention aims to provide an apparatus for the elemental analysis of a sample under consideration, of the type described above, which limits or even eliminates the drawbacks caused by the injection of a gas jet into the plasma.

[0026] The present invention also aims to limit or even eliminate deposition of optical fiber particles due to dust coming from the plasma.

[0027] The present invention also aims to provide such an analytical device with reduced gas consumption. [Means for solving the problem]

[0028] This object, and others mentioned below, are achieved by the invention, which is directed to an apparatus for the elemental analysis of a sample under consideration, said apparatus comprising: a base intended to support the sample under consideration; a system for generating a laser beam intended to impinge on the sample to generate a plasma that generates light emission, the system being configured to focus the laser beam into a focusing zone; - a means for collecting luminescence comprising an optical fiber having a free end extending along a first optical axis directed towards the focusing zone, the luminescence being intended to be collected via the free end; - means for injecting a gas jet at the sample under study, comprising a needle for injecting a gas jet, the needle having an end extending along an injection axis directed towards the focusing zone; Equipped with According to an orthogonal projection onto a plane inscribed by the base, i.e., the so-called base plane, the part of the injection axis located on the injection needle side relative to the focusing zone forms an angle of less than 90 degrees with the part of the first optical axis located on the optical fiber side relative to the focusing zone; The device is characterized in that it comprises means for moving the sample, configured to move the focusing zone on the surface of the sample according to a movement vector Sd that, according to an orthogonal projection onto a plane inscribed by the surface of the sample, forms an angle of less than or equal to 90 degrees with the ejection vector Sp of the gas jet along the ejection axis.

[0029] Due to the design of the device according to the invention, the means for injecting a gas jet make it possible to limit or even remove deposits on the optical fiber in addition to limiting deposits on the focusing means.

[0030] This is because the relative positioning of the injection needle with respect to the optical fiber and its free end allows the gas jet to sweep debris from the plasma in a direction opposite to that of the free end of the optical fiber relative to the plasma.

[0031] This configuration therefore makes it possible to limit deposits on the focusing means and the free ends of the optical fibers, while benefiting from the advantages of a gas jet such as a plasma sheath.

[0032] Advantageously, when orthogonally projected onto the base plane inscribed by the base, the portion of the injection axis located on the injection needle side relative to the focusing zone forms an angle between 30 and 90 degrees with the portion of the first optical axis located on the optical fiber side relative to the focusing zone.

[0033] This makes the advantages provided by the present invention even more pronounced.

[0034] According to a preferred design, when orthogonally projected onto the base plane inscribed by the base, the portion of the injection axis located on the injection needle side relative to the focusing zone forms a 45 degree angle with the portion of the first optical axis located on the optical fiber side relative to the focusing zone.

[0035] By this preferred embodiment, the advantages of the angle formed by the injection axis with the first optical axis are optimized and the disadvantages are minimized.

[0036] According to a preferred feature, in the plane inscribed by the ejection axis, the so-called inclined plane, which is perpendicular to the base plane, the ejection axis forms an acute angle of less than 30 degrees with the base plane.

[0037] Thus, the tilt of the injection needle contributes to improving the benefits of the present invention.

[0038] According to a preferred solution, the open end of the injection needle is positioned at a distance from the focusing zone, according to an orthogonal projection onto the base plane, that is greater than the distance of the free end of the optical fiber relative to the focusing zone.

[0039] The gas jet thus makes it possible to surround the plasma, improve the sheath and better dispel dust that can be directed towards the end of the optical fiber.

[0040] According to an advantageous embodiment, the means for injecting the gas jet has a flow rate of 1 L min -1 Flow rate less than 0.5 L min -1 and the injection needle has at its end an internal diameter of less than 1 mm, preferably equal to 0.5 mm.

[0041] In this way, gas savings are achieved compared to prior art techniques.

[0042] Additionally, it has been found that this configuration allows for a better impact of the gas jet on the plasma due to the higher velocity of the gas jet, resulting in better rejection of plasma-derived dust and reduced fouling of the optical fiber and focusing means.

[0043] This brings the end of the optical fiber closer to the plasma, improving the quality of the analysis.

[0044] The present invention also relates to a method for elemental analysis of a sample under consideration, said method comprising the steps of: - a step of injecting a gas jet onto a sample under study and a step of focusing a laser beam on said sample under study in a focusing zone in order to generate a plasma on the surface of said sample, said steps being carried out simultaneously, the gas jet being injected along an injection axis directed towards the focusing zone, and the emitted light being intended to be collected via a free end; analyzing a spectrum of the optical emission emitted by the plasma using an optical fiber having a free end extending along a first optical axis directed toward the focal zone; determining the elemental composition of the sample from this analysis of the spectrum; Including, During the step of injecting the gas jet, a portion of the injection axis located on the injection needle side relative to the focusing zone forms an angle of less than 90 degrees with a portion of the first optical axis located on the optical fiber side relative to the focusing zone, according to an orthogonal projection onto a plane inscribed on the surface of the sample; The method is characterized in that it comprises a step of changing the position of the sample under consideration according to a movement vector that, according to its orthogonal projection onto a plane inscribed by the surface of the sample, forms an angle of less than 90 degrees, preferably 0 degrees, with respect to the injection vector of the gas jet along the injection axis.

[0045] This method makes it possible to produce the same advantageous effects as the previously described device.

[0046] The step of repositioning the sample may be performed after the initial focusing of the laser beam and the initial injection of the gas jet, or as the focusing of the laser beam and the injection of the gas jet progresses.

[0047] This step allows the analysis of the sample surface to be carried out on a part of this surface that is not subject to dust accumulation after the ejection of dust by the gas jet.

[0048] Advantageously, during the step of injecting the gas jet, the gas jet has a flow rate of 1 L min -1 Flow rate less than 0.5 L min -1 flow rate of 21 m s -1 Higher speeds, preferably 42 m s -1 is ejected at a velocity equal to

[0049] This allows gas savings to be achieved along with improved protection given to the optical fiber and the focusing means against the risk of deposits, and also makes it possible to bring the optical fiber closer to the plasma being generated, improving the quality of the analysis performed.

[0050] Other characteristics and advantages of the invention will appear on reading the following description of various preferred embodiments of the invention, given by way of illustrative and non-limiting example, and will also become apparent from the accompanying drawings, in which: [Brief explanation of the drawings]

[0051] [Figure 1] 1 is a schematic diagram of an apparatus for elemental analysis of a sample under study by optical emission spectroscopy on a laser-produced plasma according to the present invention; [Figure 2] 1 is a schematic diagram of an orthogonal projection onto a base plane of the relative positioning of the injection needle of the gas jet and the optical fiber of the device relative to the plasma intended to be generated by the device; [Figure 3] FIG. 10 is a schematic diagram of a beveled surface showing the inclination of the needle relative to the base plane. [Figure 4]FIG. 10 is a schematic diagram showing the changing of the position of the sample during analysis to move the focal area. DETAILED DESCRIPTION OF THE INVENTION

[0052] Referring to FIG. 1, an apparatus for elemental analysis of a sample 2 under consideration according to the present invention is shown.

[0053] The device comprises a base 1 intended to support a sample 2 to be studied.

[0054] This base 1 has, inter alia, an upper surface 10 on which the sample 2 rests.

[0055] The sample 2 is more particularly mounted in a sample holder which allows the sample 2 to have a planar surface to be considered which extends parallel to the upper surface 10 of the base 1.

[0056] As a preliminary observation, Figure 2 shows a schematic orthogonal projection of the components of the device described in more detail below, and more particularly the orientation of these components, onto a plane inscribed by the base 1, the so-called base plane B. More precisely, with reference to Figure 3, the upper surface 10 of the base 1 is inscribed in the base plane B.

[0057] The apparatus also comprises a system 3 for generating a laser beam 31 intended to impinge on the sample 2 and generate a plasma P which generates an optical emission 30 .

[0058] This generation system 3 comprises a module for generating a laser beam 31 and, notably, a module for focusing the laser beam 31 .

[0059] The generating system 3 is configured to focus the laser beam 31 into a focusing zone 310 .

[0060] More specifically, the generating system 3 is configured to emit a laser beam perpendicular to the top surface 10 of the base 1. The laser beam 31 is therefore emitted perpendicular to the planar surface of the sample 2 under consideration.

[0061] The focal zone 310 essentially corresponds to the origin of the generation of the plasma P.

[0062] As previously mentioned, the laser beam 31 generates a plasma P that produces an emission 30. This emission 30 corresponds to optical radiation.

[0063] The device also comprises means 4 for collecting the emitted light 30, as shown in FIG.

[0064] 1 to 3, the collecting means 4 comprises an optical fiber 41 having a free end 410 extending along a first optical axis 411 oriented towards the focusing zone 310 .

[0065] The emitted light 30 is therefore collected via the free end 410 as close as possible to the plasma P.

[0066] The closer the free end 410 of the optical fiber 41 is to the plasma P, the better the collection of the emitted light 30 will be, to the benefit of the quality of the analysis.

[0067] On the other hand, the closer the free end 410 of the optical fiber 41 is to the plasma P, the higher the risk of deposits at this free end 410 due to dust generated by the plasma P.

[0068] With reference to Figures 1 to 3, the device comprises means 5 for injecting a gas jet onto the sample 2 under consideration.

[0069] These injection means 5 comprise a needle 51 for injecting a gas jet.

[0070] The injection needle 51 has an end 510 extending along an injection axis 511 pointing towards the focus zone 310 .

[0071] This injection needle 51 makes it possible to inject a gas jet into the plasma P, improving the quality of the analysis as previously described.

[0072] This gas jet thus generates a sheath of plasma P.

[0073] The gas jet has the particularity of not only limiting the deposits on the focusing lens of the generating system 3 but also on the free end 410 of the optical fiber 41 .

[0074] In fact, as shown in Figure 2, when orthogonally projected onto the base plane B, the portion of the injection axis 511 located on the injection needle 51 side relative to the focal zone 310 forms an angle A1 of less than 90 degrees with the portion of the first optical axis 411 located on the optical fiber 41 side relative to the focal zone 310.

[0075] More specifically, the angle A1 is between 30 and 90 degrees.

[0076] More precisely, the angle A1 is 45 degrees.

[0077] 3, a plane called the inclined plane is shown, which indicates the inclination of the injection needle 51 relative to the base plane B. This inclined plane is also represented in FIG. 2 by the section line III-III, which coincides with the injection axis 511.

[0078] As a result, the ejection axis 511 is inscribed in this inclined surface, which extends perpendicular to the base plane B.

[0079] This inclined surface causes the ejection axis 511 to form an acute angle A3 with the base plane B of less than 30 degrees.

[0080] Referring to FIG. 2, the injection needle 51 is substantially retracted relative to the free end 410 of the optical fiber 41 .

[0081] In fact, when projected orthogonally onto the base plane B, the open end 512 of the injection needle 51 is positioned at a distance from the focal zone 310 that is greater than the distance of the end 410 of the optical fiber 41 from the focal zone 310.

[0082] 2 by circles R1 and R2 centered on the focal zone 310. The free end 410 of the optical fiber 41 is positioned on the circle R1 having a diameter d1, and the open end 512 of the injection needle 51 is positioned on the circle R2 having a diameter d2.

[0083] According to this principle, the diameter d2 of the circle R2 is strictly greater than the diameter d1 of the circle R1.

[0084] In order to minimize gas consumption and improve the quality of the gas jet injection, the gas jet injection means 5 is then set to a value of 1 L min -1 The injection needle 51 is configured to inject a gas jet at a flow rate of less than 1 mm, and has an inner diameter at its end 510 of less than 1 mm.

[0085] More specifically, the injection means 5 has a flow rate of 0.5 L·min -1 and the injection needle 51 has an internal diameter at its end 510 equal to 0.5 mm.

[0086] In this way, the gas jet is injected at a particularly high speed and low flow rate, which minimizes gas consumption and optimizes the effect produced by the gas on the plasma P compared to what is proposed in the prior art.

[0087] This is because the fiber optic cable is better sheathed and protected from fouling.

[0088] In this way, the optical fiber can be brought closer to the plasma P, and the resolution and quality of the analysis can also be improved.

[0089] The above-described device makes it possible to carry out a method for elemental analysis of a sample under study, which comprises simultaneously injecting a sample gas jet under study and focusing a laser beam 30 in a focal zone 310 on the sample under study 2.

[0090] The focusing step makes it possible to generate a plasma P on the surface of this sample 2, with a gas jet being ejected along an ejection axis 511 pointing towards the focusing zone 310. This ejection axis 511 corresponds to the orientation of the ejection needle 51.

[0091] The method also includes a step of analyzing the spectrum of the emission corresponding to the optical radiation emitted by the plasma P. This analysis step is performed by capturing this emission by an optical fiber 411 having a free end 410 extending along a first optical axis 411 directed towards the focal zone 310.

[0092] Finally, the analytical method includes determining a spectrum of the elemental composition of the sample from the analysis.

[0093] The method presents the parameters of the aforementioned device during the step of injecting the gas jet, in particular the parameters relating to the first optical axis 411 and the angle that the injection axis 511 makes with respect to the base plane B.

[0094] Additionally, during the step of injecting the gas jet, the gas jet is 1 L min -1 Flow rate less than 0.5 L min -1 and at a velocity greater than 21 meters per second, preferably equal to 42 meters per second.

[0095] As illustrated by FIG. 4, the method also includes a step of changing the position of the sample 2 under consideration.

[0096] This variation step is performed to move the focus zone 310 on the surface of the sample 2 .

[0097] According to an orthogonal projection onto a plane inscribed by the surface of the sample, the change in position of the sample 2 under study is carried out according to a movement vector Sd that forms an angle of less than 90 degrees with respect to the injection vector Sp of the gas jet along the injection axis 511.

[0098] As shown, the movement of the sample 2 according to the movement vector Sd allows the position of the focus zone 310 to be changed according to a movement D to bring the focus zone 310 to a new position 310'.

[0099] In other words, the sample 2 is moved laterally or forward during analysis according to the ejection vector Sp of the gas jet in order to retract the focal zone 310 to a portion of the sample that is not covered by the plasma dust displaced by the gas jet.

[0100] This step is also carried out by the device described above, which comprises means for moving the sample, and which is adapted to carry out this modification step.

Claims

1. a base (1) for supporting a sample (2) to be studied; a system (3) for generating a laser beam (31) for generating a plasma (P) that impinges on the sample (2) and generates an optical emission (30), the system (3) being configured to focus the laser beam (31) in a focusing zone (310); a means (4) for collecting the luminescence (30), comprising an optical fiber (41) having a free end (410) extending along a first optical axis (411) directed towards the focusing zone (310), the luminescence (30) being intended to be collected via the free end (410); means (5) for injecting said gas jet into said sample (2) under study, said means (5) comprising a needle (51) for injecting a gas jet, said needle (51) having an end (510) extending along an injection axis (511) directed towards said focusing zone (310); An apparatus for elemental analysis of a sample under consideration, comprising: According to an orthogonal projection onto a plane inscribed by the base (1), i.e., the base plane (B), the part of the injection axis (511) located on the injection needle (51) side relative to the focusing zone (310) forms an angle (A1) of 90 degrees or less with the part of the first optical axis (411) located on the optical fiber (41) side relative to the focusing zone (310). The features are:

1. The apparatus according to claim 1, further comprising means for moving the sample, the means being configured to move the focusing zone (310) on the surface of the sample (2) according to a movement vector (Sd) which, according to an orthogonal projection onto a plane inscribed by the surface of the sample, forms an angle of less than or equal to 90 degrees with an ejection vector (Sp) of the gas jet along the ejection axis (511).

2. 10. The device according to claim 1, characterized in that, according to an orthogonal projection onto the base plane (B) inscribed by the base (1), the part of the injection axis (511) lying on the side of the injection needle (51) with respect to the focusing zone (310) forms an angle (A1) between 30 and 90 degrees with the part of the first optical axis (411) lying on the side of the optical fiber (41) with respect to the focusing zone (310).

3. 10. The device according to claim 1, characterized in that, according to an orthogonal projection onto the base plane (B) inscribed by the base (1), the part of the injection axis (511) located on the side of the injection needle (51) relative to the focusing zone (310) forms an angle (A1) of 45 degrees with the part of the first optical axis (411) located on the side of the optical fiber (41) relative to the focusing zone (310).

4. 10. A device according to any one of the preceding claims, characterized in that in the plane in which the injection axis (511) is inscribed, i.e. the inclined plane, which is perpendicular to the base plane (B), the injection axis (511) forms an acute angle (A3) of less than or equal to 30 degrees with the base plane (B).

5. 10. A device according to any one of the preceding claims, characterized in that, according to an orthogonal projection onto the base plane (B), the open end (512) of the injection needle (51) is positioned at a distance from the focusing zone (310) that is greater than the distance of the free end (410) of the optical fiber (41) relative to the focusing zone (310).

6. The means (5) for injecting the gas jet has a flow rate of 1 L min －１ Flow rate less than 0.5 L min －１ 10. A device according to any one of the preceding claims, characterized in that the injection needle (51) is configured to inject the gas jet with a flow rate of 0.5 mm, and in that the injection needle (51) has at its end (510) an internal diameter of less than 1 mm, preferably equal to 0.5 mm.

7. 1. A method for elemental analysis of a sample under study, comprising: - injecting a gas jet onto the sample (2) under study and focusing a laser beam (31) on the sample (2) under study in a focusing zone (310) in order to generate a plasma (P) on the surface of this sample, these steps being performed simultaneously, the gas jet being injected along an injection axis (511) directed towards the focusing zone (310); analyzing the spectrum of the optical emission emitted by the plasma using an optical fiber (41) having a free end (410) extending along a first optical axis (411) directed towards the focusing zone (310), the optical emission (30) being intended to be collected via the free end (410); determining the elemental composition of the sample from this analysis of the spectrum; A method comprising: During the step of injecting the gas jet, according to an orthogonal projection onto a plane inscribed by the surface of the sample, a portion of the injection axis (511) located on the injection needle (51) side relative to the focusing zone (310) forms an angle (A1) of less than 90 degrees with a portion of the first optical axis (411) located on the optical fiber (41) side relative to the focusing zone (310), The method is characterized in that it comprises a step of changing the position of the sample (2) under consideration according to a movement vector (Sd) which, according to its orthogonal projection onto a plane inscribed by the surface of the sample (2), forms an angle of less than or equal to 90 degrees, preferably 0 degrees, with respect to the injection vector (Sp) of the gas jet along the injection axis (511).

8. During the step of injecting the gas jet, the gas jet is 1 L min －１ Flow rate less than 0.5 L min －１ flow rate of 21 m s －１ a speed higher than 42 m·s －１ 8. The method of claim 7, wherein the gas is injected at a velocity equal to

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