A dual-beam LAAS isotopic ratio high-precision rapid measuring device and method

Abstract

The application discloses a kind of double-beam LAAS isotopic ratio high-precision fast measuring device and method, the device includes: second light splitting piece is used to first tunable laser light, after splitting, a small part enters first photoelectric detector, most enters first polarized beam splitter prism;Third light splitting piece is used to second tunable laser light after passing through second reflector, after splitting, a small part enters second photoelectric detector, most enters first polarized beam splitter prism;First photoelectric detector and second photoelectric detector are used to measure the intensity of first tunable laser light and second tunable laser light entering it respectively;Third photoelectric detector and fourth photoelectric detector are used to measure the intensity of first tunable laser light and second tunable laser light entering it respectively.The application greatly improves isotopic ratio measurement precision, and without laser wavelength scanning, without calibration, it can realize fast direct measurement to isotopic ratio.

Description

Technical Field

[0001] This invention relates to the field of isotope detection technology, and in particular to a dual-beam LAAS isotope ratio high-precision and rapid measurement device and method. Background Technology

[0002] Precise measurement of isotope ratios has wide applications in nuclear material testing, geological research, marine science, and environmental science. Particularly in nuclear fuel production, nuclear safeguards, environmental monitoring, and nuclear forensic investigations, precise measurement of isotope ratios is a crucial analytical method. Laser ablation absorption spectroscopy (LAAS), which combines laser ablation plasma with absorption spectroscopy, utilizes a tunable laser to detect the absorption transitions of ground-state atoms and ions during the cooling phase of plasma formed by pulsed laser ablation. This allows for high-resolution, high-sensitivity spectroscopic analysis, making it highly suitable for isotope-resolved spectral measurements. LAAS measurements require no sample pretreatment, are easy to operate, and offer fast analysis speeds. They are readily available for online, remote, and real-time measurements, making them an important tool for measuring radioactive isotope ratios in applications such as the nuclear fuel cycle. In 1999, the University of Florida (UF) first proposed a method for measuring isotope ratios using LAAS technology, measuring ratios from basalt grains with an Rb content of 77±5 ppm. 85 Rb / 87 The Rb value is 2.8 ± 0.3%, and the relative standard deviation (RSD) is less than 5%, providing a simple analytical tool for geological research and age analysis. In 2002, the Institute for Spectrochemistry and Applied Spectroscopy (ISAS) in Germany proposed a dual-beam LAAS technique for direct detection of isotope ratios. They tuned the wavelengths of two independent tunable lasers to the resonance absorption peaks of the target isotopes, and inferred the target isotope ratio in the material by measuring the ratio of the absorption intensities of the two laser beams. Using this method, ISAS can directly detect isotope ratios in geological research. 235 U / 238 The measurement accuracy of the U ratio is better than 5%. This work shows that the dual-beam fixed-wavelength method can avoid the time-consuming laser wavelength scanning process, simultaneously detect two isotope signals under the same plasma conditions, and that there is a correlation between the absorption signals of the isotopes. Therefore, it greatly improves the measurement efficiency and reduces the influence of laser-plasma variations on the measurement results. However, in their work, the two laser beams are intersected at a small angle, and the plasma regions acted by the two lasers are not completely consistent. Therefore, the RSD of multiple measurements exceeded 17%, and the isotope discrimination effect was not considered.

[0003] my country is vigorously developing its nuclear power industry and researching new methods for nuclear waste disposal. There is a huge demand for highly sensitive and precise online rapid measurement technology for radioactive element isotope ratios in areas such as uranium ore exploration and mining, nuclear fuel production, safe operation of nuclear power plants, and spent nuclear fuel disposal. Developing high-precision, high-sensitivity LAAS isotope ratio online detection technology with domestically developed core components is of great significance to my country's nuclear power, nuclear energy applications, and nuclear waste disposal; however, there is currently almost no related work in China.

[0004] In summary, although current LAAS technology has enabled the detection of radioactive isotope ratios in the laboratory, it lacks a rapid method for determining isotope ratios and its accuracy and sensitivity are insufficient for applications such as nuclear forensics. Furthermore, in laser resonance ionization experiments on elements such as uranium, it has been found that different linewidth lasers significantly affect the resonance excitation efficiency and detection sensitivity of atoms due to factors such as atomic spectral line broadening and the varying hyperfine structure splitting characteristics of different isotopes. Isotopes with different hyperfine structures exhibit significant differences in absorption efficiency to detection lasers with the same linewidth; this effect is called isotope discrimination. However, when simultaneously measuring isotope ratios with dual-beam lasers, commercially available lasers typically have uniform linewidths, leading to substantial differences in the absorption characteristics of different isotopes, which is a significant factor affecting the uncertainty of isotope analysis. No research reports have yet documented this isotope discrimination effect caused by laser linewidth in LAAS experiments.

[0005] A similar experimental approach to this invention is the dual-beam LAAS direct isotope ratio detection technique proposed by the Institute for Spectrochemistry and Applied Spectroscopy (ISAS) in Germany. They tuned the wavelengths of two independent tunable semiconductor lasers to the resonance absorption peaks of the target isotopes, and then determined the target isotope ratio in the material by measuring the ratio of the absorption intensities of the two laser beams. Using this method, ISAS... 235 U / 238 The measurement accuracy of the U ratio is better than 5%. The experimental scheme proposed by ISAS improves the efficiency of isotope ratio measurement and reduces the influence of laser plasma changes on the measurement results. However, in their scheme, from a technical perspective, the two probe lasers are combined at a small angle, and the plasma regions acted by the two lasers are not completely consistent. Therefore, the error of multiple measurements exceeds 17%. From a physical mechanism perspective, this study does not consider the isotope discrimination effect, which also limits the measurement accuracy. Furthermore, the scheme uses a semiconductor laser as the probe light source, which has a limited wavelength tuning range and can usually only measure isotopes of 1 to 2 elements, thus limiting the scope of technical application. Summary of the Invention

[0006] To address the shortcomings of existing dual-laser absorption spectroscopy (LAAS) methods for measuring isotope ratios, such as differences in the interaction regions of the two probe lasers with spatially inhomogeneous plasmas, inconsistent states, lack of consideration for isotope discrimination effects, low measurement efficiency due to the need for scanning laser wavelengths, and limited range of measurable elements, this invention provides a high-precision and rapid method for measuring LAAS isotope ratios using dual-pulse beams with different linewidths. By combining the polarized beams of two lasers and passing them through the same spatiotemporal region to detect the isotope ratio, this method improves efficiency and reduces or eliminates laser-induced isotope discrimination effects.

[0007] This invention discloses a dual-beam LAAS isotope ratio high-precision and rapid measurement device, which includes: a nanosecond pump laser, used to simultaneously pump a first tunable laser and a second tunable laser through a first beam splitter and a first reflector to generate two tunable laser beams, referred to as the first tunable laser and the second tunable laser respectively.

[0008] The first half-wave plate and the second half-wave plate are used to make the polarization states of the first tunable laser and the second tunable laser perpendicular to each other.

[0009] The second beam splitter is used to split the first tunable laser beam. After splitting, a small portion enters the first photodetector, and the majority enters the first polarization beam splitter.

[0010] The third beam splitter is used to split the second tunable laser after it has passed through the second reflector. After splitting, a small part of the laser enters the second photodetector and the majority of the laser enters the first polarization beam splitter.

[0011] The first photodetector and the second photodetector are used to measure the original intensity of the first tunable laser and the second tunable laser entering them by proportional conversion, respectively.

[0012] The first polarization beam splitter is used to combine the first tunable laser and the second tunable laser entering it into a collinear laser beam.

[0013] The second polarization beam splitter is used to separate the collinear laser beams that have passed through the plasma plume region above the surface of the sample to be tested, so as to obtain the first tunable laser and the second tunable laser beam after separation.

[0014] The third and fourth photodetectors are used to measure the residual intensity of the first and second tunable lasers entering them, respectively.

[0015] Furthermore, the first half-wave plate is disposed between the first tunable laser and the second beam splitter;

[0016] The second beam splitter is disposed between the first half-wave plate and the first polarizing beam splitter prism, and between the first half-wave plate and the first photodetector.

[0017] Furthermore, the second half-wave plate is disposed between the second tunable laser and the second mirror;

[0018] The third beam splitter is disposed between the second reflector and the first polarizing beam splitter prism, and between the second reflector and the second photodetector.

[0019] Furthermore, it also includes a data processing device;

[0020] The data processing device is used to obtain the ratio of the two isotopes of the target element in the sample to be tested based on the difference between the original intensity and the residual intensity of the first tunable laser measured by the third photodetector and the first photodetector, and the difference between the original intensity and the residual intensity of the second tunable laser measured by the fourth photodetector and the second photodetector.

[0021] Furthermore, the first tunable laser and the second tunable laser can use gratings with different scribe lines to obtain laser outputs with different linewidths; wherein the linewidth of the output laser is matched with the spectral linewidth of the two isotopes of the target element in the sample to be tested.

[0022] This invention also discloses a high-precision and rapid method for measuring the isotope ratio of a dual-beam LAAS, applicable to the aforementioned high-precision and rapid measurement device for the dual-beam LAAS isotope ratio, comprising:

[0023] The laser emitted by the nanosecond pump laser is split by the first beam splitter and reflected by the first mirror, and then simultaneously pumps the first tunable laser and the second tunable laser to generate two tunable laser beams, which are referred to as the first tunable laser and the second tunable laser, respectively.

[0024] The first half-wave plate and the second half-wave plate are used to make the polarization states of the first tunable laser and the second tunable laser perpendicular to each other; then, after the first tunable laser passes through the second beam splitter, a small portion enters the first photodetector to measure the intensity of the first tunable laser, and the majority enters the first polarizing beam splitter prism; after the second tunable laser passes through the second mirror and the third beam splitter in sequence, a small portion enters the second photodetector to measure the intensity of the second tunable laser, and the majority enters the first polarizing beam splitter prism;

[0025] The first polarization beam splitter combines the first and second tunable lasers entering it into a collinear laser beam. The collinear laser beam passes through the plasma plume region above the surface of the sample under test. The two wavelengths of the laser resonate and are absorbed by two isotopes in the sample under test in the plasma plume, respectively. After passing through the second polarization beam splitter, the collinear laser beam is separated into the first and second tunable lasers, which then act on the third and fourth photodetectors respectively to measure the pulse intensity.

[0026] The ratio of the two isotopes of the target element in the sample to be tested is obtained by comparing the intensity difference between the first tunable laser measured by the third photodetector and the first photodetector, and the intensity difference between the second tunable laser measured by the fourth photodetector and the second photodetector.

[0027] Furthermore, the linewidths of the first tunable laser and the second tunable laser are controlled by grating lines in the second tunable laser and the first tunable laser, respectively.

[0028] Furthermore, the surface of the sample under test is ablated by an ablation laser output from a short-pulse laser to generate a plasma plume.

[0029] Furthermore, the linewidths of the first tunable laser and the second tunable laser are different, and they match the spectral linewidths of the two isotopes of the target element in the sample to be tested.

[0030] Because of the adoption of the above technical solution, the present invention has the following advantages:

[0031] 1. Due to the rapid expansion and evolution of the plasma plume formed by pulsed laser ablation over time, its spatiotemporal distribution is highly non-uniform, significantly impacting isotope ratio measurements. Existing international dual-beam LAAS detection experiments employ continuous laser detection, with two laser beams incident at a small angle into the plasma plume region. Consequently, the plasma regions and states affected by the two laser beams are not entirely identical, leading to RSDs exceeding 17% in multiple measurements, which is insufficient for practical applications. In this invention, the project team combines two polarized laser beams and passes them through identical spatiotemporal regions to detect isotope ratios. This allows for the acquisition of absorption intensity at the same time and in the same space, greatly improving the accuracy and efficiency of isotope ratio measurements.

[0032] 2. Due to the potential for different isotopes to possess different hyperfine structures, and the influence of spectral line broadening mechanisms in plasmas, isotope discrimination may occur when probe lasers of the same linewidth interact with isotopes. Currently, there are no reported experimental studies on this in LAAS research. In this invention, the project team will develop lasers with different linewidths based on the energy level structure characteristics of different target isotopes. By selecting two probe lasers with different linewidths for dual-pulse LAAS isotope ratio measurement, the isotope discrimination effect can be significantly reduced or eliminated, enabling direct and high-precision dual-beam LAAS measurement of the radioactive isotope ratio in plasma.

[0033] 3. This scheme uses two solid-state tunable lasers as the detection light source, which has a wider tuning range than commonly used semiconductor lasers. Therefore, a single device can be used to accurately measure the isotope ratio of multiple elements, greatly improving the application range of this method.

[0034] 4. This invention can effectively overcome the isotope discrimination effect of isotopes with ultrafine structures in laser absorption and the inconsistency of plasma measurement regions in traditional dual-beam measurement methods, thereby greatly improving the accuracy of isotope ratio measurement; this method can achieve rapid and direct measurement of isotope ratio without laser wavelength scanning or calibration; the solid-state narrow linewidth tunable laser used is suitable for various isotope analyses. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in the embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0036] Figure 1 This is a schematic diagram of a device for high-precision and rapid measurement of uranium isotope ratio using dual-beam LAAS, according to an embodiment of the present invention.

[0037] Figure 2 As described in the embodiments of the present invention 235 U and 238 A schematic diagram of the 714nm transition line of U;

[0038] Figure 3 Rapid Measurement of Dual-Beam LAAS Isotope Ratios in Embodiments of the Invention 235 U / 238 Schematic diagram of U;

[0039] Figure 4 Uranium isotopes as described in this embodiment of the invention 235 U / 238A schematic diagram illustrating the implementation of high-precision, rapid measurement of the U-ratio.

[0040] Icon labels:

[0041] 1-Nanosecond pumped laser, 2-First beam splitter, 3-First reflector, 4-First tunable laser, 5-Second tunable laser, 6-First half-wave plate, 7-Second half-wave plate, 8-First photodetector, 9-Second beam splitter, 10-First polarizing beam splitter prism, 11-Third beam splitter, 12-Second reflector, 13-Second photodetector, 14-Ablation laser, 15-Plasma plume region, 16-Sample under test, 17-Second polarizing beam splitter prism, 18-Fourth photodetector, 19-Third photodetector, 20-First frequency doubling crystal, 21-Second frequency doubling crystal, 22-First narrow-linewidth tunable Ti:sapphire solid-state laser, 23-Second narrow-linewidth tunable Ti:sapphire solid-state laser. Detailed Implementation

[0042] The present invention will be further described in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art should fall within the protection scope of the present invention.

[0043] See Figure 1 This invention provides an embodiment of a dual-beam LAAS isotope ratio high-precision rapid measurement device, comprising: a nanosecond pump laser 1, a first beam splitter 2, a second beam splitter 9, a third beam splitter 11, a first tunable laser 4, a second tunable laser 5, a first half-wave plate 6, a second half-wave plate 7, a first photodetector 8, a second photodetector 13, a third photodetector 19, a fourth photodetector 18, a first polarizing beam splitter prism 10, a second polarizing beam splitter prism 17, a sample to be measured 16, a first reflector 3, and a second reflector 12;

[0044] The nanosecond pump laser 1 is used to simultaneously pump the first tunable laser 4 and the second tunable laser 5 through the first beam splitter 2 and the first reflector 3, respectively, to generate two tunable laser beams, which are referred to as the first tunable laser and the second tunable laser, respectively.

[0045] The first half-wave plate 6 and the second half-wave plate 7 are used to make the polarization states of the first tunable laser and the second tunable laser perpendicular to each other.

[0046] The second beam splitter 9 is used to split the first tunable laser beam. After splitting, a small portion enters the first photodetector 8, and the majority enters the first polarization beam splitter prism 10.

[0047] The third beam splitter 11 is used to split the second tunable laser after passing through the second reflector 12. After splitting, a small part enters the second photodetector 13, and most of it enters the first polarization beam splitter 10.

[0048] The first photodetector 8 and the second photodetector 13 are used to measure the intensity of the first tunable laser and the second tunable laser entering them, respectively.

[0049] The first polarization beam splitter 10 is used to combine the first tunable laser and the second tunable laser entering it into a collinear laser beam.

[0050] The second polarization beam splitter prism 17 is used to separate the collinear laser beams that pass through the plasma plume region 15 in the region above the surface of the sample to be tested 16, so as to obtain the first tunable laser and the second tunable laser beam after separation.

[0051] The third photodetector 19 and the fourth photodetector 18 are used to measure the intensity of the first tunable laser and the second tunable laser entering them, respectively.

[0052] In this embodiment, the first half-wave plate 6 is disposed between the first tunable laser 4 and the second beam splitter 9;

[0053] The second beam splitter 9 is disposed between the first half-wave plate 6 and the first polarizing beam splitter prism 10, and between the first half-wave plate 6 and the first photodetector 8.

[0054] In this embodiment, the second half-wave plate 7 is disposed between the second tunable laser 5 and the second reflector 12;

[0055] The third beam splitter 11 is disposed between the second reflector 12 and the first polarizing beam splitter 10, and between the second reflector 12 and the second photodetector 13.

[0056] In this embodiment, a data processing device is also included;

[0057] The data processing device is used to obtain the ratio of the two isotopes of the target element in the sample 16 to be tested based on the difference in intensity of the first tunable laser measured by the third photodetector 19 and the first photodetector 8, and the difference in intensity of the second tunable laser measured by the fourth photodetector 18 and the second photodetector 13.

[0058] In this embodiment, the first tunable laser 4 and the second tunable laser 5 are both used to obtain laser outputs with different linewidths using gratings with different scribe lines; wherein, the linewidth of the output laser matches the spectral linewidth of the two isotopes of the target element in the sample 16 to be tested.

[0059] This invention also provides an embodiment of a high-precision rapid measurement method for dual-beam LAAS isotope ratios, applicable to the above-described embodiment of the high-precision rapid measurement device for dual-beam LAAS isotope ratios, comprising:

[0060] The laser emitted by the nanosecond pump laser 1 is split by the first beam splitter 2 and reflected by the first mirror 3, and then simultaneously pumps the first tunable laser 4 and the second tunable laser 5 to generate two tunable laser beams, which are referred to as the first tunable laser and the second tunable laser, respectively.

[0061] The first half-wave plate 6 and the second half-wave plate 7 are used to make the polarization states of the first tunable laser and the second tunable laser perpendicular to each other; then, after the first tunable laser passes through the second beam splitter 9, a small portion enters the first photodetector 8 to measure the intensity of the first tunable laser, and the majority enters the first polarizing beam splitter prism 10; after the second tunable laser passes through the second reflector 12 and the third beam splitter 11 in sequence, a small portion enters the second photodetector 13 to measure the intensity of the second tunable laser, and the majority enters the first polarizing beam splitter prism 10.

[0062] The first polarization beam splitter 10 combines the first tunable laser and the second tunable laser entering it into a collinear laser beam. The collinear laser beam passes through the plasma plume region 15 above the surface of the sample 16 to be tested. The two wavelengths of laser light resonate and are absorbed by two isotopes in the sample 16 to be tested in the plasma plume. After passing through the second polarization beam splitter again, the collinear laser beam is separated into the first tunable laser and the second tunable laser, which act on the third photodetector 19 and the fourth photodetector 18 respectively to measure the pulse intensity.

[0063] The ratio of the two isotopes of the target element in the sample 16 to be tested is obtained based on the difference in intensity of the first tunable laser measured by the third photodetector 19 and the first photodetector 8, and the difference in intensity of the second tunable laser measured by the fourth photodetector 18 and the second photodetector 13.

[0064] Specifically, the ratio of the intensity difference of the first tunable laser measured by the third photodetector 19 and the first photodetector 8 to the intensity difference of the second tunable laser measured by the fourth photodetector 18 and the second photodetector 13 is the ratio of the two isotopes in the sample 16 to be tested. When the first and second tunable lasers pass through the plasma plume region 15 above the sample 16 to be tested, portions of them are absorbed by the two isotopes of the target element in the sample 16, respectively.

[0065] In this embodiment, the linewidths of the first tunable laser and the second tunable laser are controlled by grating lines in the first tunable laser 4 and the second tunable laser 5, respectively.

[0066] In this embodiment, the surface of the sample 16 to be tested is ablated by the ablation laser 14 output by the short pulse laser to generate a plasma plume.

[0067] In this embodiment, the linewidths of the first tunable laser and the second tunable laser are different, and they match the spectral linewidths of the two isotopes of the target element in the sample 16 to be tested.

[0068] For ease of understanding, this invention provides a method when the isotope of the target element in the sample to be tested is... 235 U and 238 An example of high-precision measurement of U.

[0069] Figure 2 yes 235 U and 238 The 714 nm transition line shape of U [Spectrochimica Acta Part B 169(2020)105828]. For example... Figure 2 As shown, due to the difference between angular momentum and nuclear spin, 238 U and 235 U exhibits various hyperfine structures. Isotopes with different hyperfine structures show significant differences in absorption efficiency for probe lasers of the same linewidth. This effect, known as isotope discrimination, is a crucial factor influencing the uncertainty of isotope analysis. Therefore, it is essential to study the absorption ratio of isotopes for probe lasers of different linewidths in order to select a probe laser with an appropriate linewidth to reduce or eliminate the influence of isotope discrimination.

[0070] like Figure 3 As shown, two tunable nanosecond pulse lasers λ1 and λ2 are used to simultaneously detect... 238 U and 235 According to Lambert-Beer's law, the absorption intensity of U is related to the absorption cross-section of the isotope being measured and the path length of the probe laser through the sample. If two laser beams pass through the same spatial region simultaneously, i.e., the interaction volume is exactly the same, then the ratio of the absorption intensities of the two isotopes is only related to the density of the isotopes in that region. Furthermore, based on the difference in light intensity contrast before and after the plasma plume incident with probe lasers of different linewidths in the figure, it can be seen that the difference in light intensity before and after the incident with a narrow-linewidth probe laser is more significant, which is more beneficial for isotope ratio measurement. Therefore, this embodiment fully utilizes the high polarization contrast characteristic of solid-state lasers, combining two narrow-linewidth tunable pulse lasers λ1 and λ2 and passing them through the plasma in the same region before measurement. 235 U and 238The absorption spectrum of U can be directly obtained by inversion of the intensity ratio. 235 U / 238 U ratio.

[0071] Figure 4 It is an isotope of uranium. 235 U / 238 A schematic diagram illustrating the implementation of high-precision, rapid measurement of the U-ratio. Figure 4 exist Figure 1 Based on this, a first frequency doubling crystal 20 and a second frequency doubling crystal 21 were added, and the first tunable laser 4 and the second tunable laser 5 were replaced with a first narrow linewidth tunable Ti:sapphire solid-state laser 22 and a second narrow linewidth tunable solid-state laser 23, respectively.

[0072] The laser generated by the nanosecond laser 1 is simultaneously pumped by the first narrow-linewidth tunable Ti:sapphire solid-state laser 22 and the second narrow-linewidth tunable Ti:sapphire solid-state laser 23 through the first beam splitter 2 and the first reflector 3 to obtain two extremely narrow-linewidth lasers (the first tunable laser and the second tunable laser) as probe lasers, with the laser wavelength precisely tuned to 788nm.

[0073] The first frequency doubling crystal 20 and the second frequency doubling crystal 21 double the tunable laser wavelength to the resonant wavelength of uranium element at 394 nm.

[0074] The first half-wave plate 6 and the second half-wave plate 7 adjust the polarization state of the two probe laser beams to make them perpendicular to each other.

[0075] The second beam splitter 9 and the third beam splitter 11 respectively split the two probe laser beams to facilitate pulse intensity measurement;

[0076] The first polarizing beam splitter 10 combines two probe laser beams with perpendicular polarization directions.

[0077] The second polarization beam splitter prism 17 splits the combined laser beam after passing through the plasma plume region 15.

[0078] The optical path propagation of the present invention is as follows: a 527nm nanosecond pump laser is split by a first beam splitter 2 and reflected by a first reflector 3, and then simultaneously pumps a first narrow-linewidth tunable Ti:sapphire solid-state laser 22 and a second narrow-linewidth tunable Ti:sapphire solid-state laser 23 to generate two narrow-linewidth lasers (a first tunable laser and a second tunable laser). These lasers, together with a first frequency doubling crystal 20 and a second frequency doubling crystal 21, generate narrow-linewidth probe lasers tuned to 390nm. The two narrow-linewidth lasers use gratings with different scribe lines to obtain laser outputs with different linewidths. By optimizing the number of grating scribe lines, the linewidth of the laser is matched with the spectral linewidth of the two isotopes. Then, the first half-wave plate 6 and the second half-wave plate 7 are used to make the polarization states of the two laser beams perpendicular to each other. After the two probe laser beams are split by the second beam splitter 9 and the third beam splitter 11, a small portion of the two beams enters the first photodetector 8 and the second photodetector 13 to measure the incident light intensity. The remaining part of the second tunable laser is reflected by the second mirror 12 and then combined with the remaining part of the first tunable laser through the first polarization beam splitter prism 10 to form a collinear laser beam. The beam passes through the plasma plume region 15 a few millimeters above the sample surface. The two wavelengths of the laser beam resonate and are absorbed by the two isotopes in the plasma plume region. After passing through a second polarization beam splitter prism 17, the two probe laser beams are separated and act on the third photodetector 19 and the fourth photodetector 18 to measure the output pulse intensity.

[0079] By using probe lasers with different linewidths, and based on the different absorption characteristics of the target isotopes to probe lasers with different linewidths, two probe lasers with appropriate linewidths were selected to perform dual-pulse LAAS isotope ratio measurements, thereby reducing or eliminating the isotope discrimination effect.

[0080] By selecting a solid-state tunable laser and making full use of its high polarization contrast, it is possible to achieve long-distance spatial beam combining and transmission of two pulsed lasers, thus avoiding measurement errors caused by the two probe lasers not acting on completely identical plasma regions.

[0081] After the light intensity measured by the photodetector is collected by the data acquisition card or oscilloscope, the calibrated outgoing and incident light intensities are differentially processed to obtain the absorption intensity of the two isotopes. The isotope ratio can be directly obtained by inverting the light intensity ratio.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A dual-beam LAAS isotopic ratio high-precision rapid measurement device, characterized in that, The method comprises the following steps: A nanosecond pump laser is used to pump a first tunable laser and a second tunable laser with laser generated by the nanosecond pump laser through a first beam splitter and a first mirror respectively, so as to generate two tunable lasers, which are recorded as a first tunable laser and a second tunable laser respectively; A first half-wave plate and a second half-wave plate are used to make the polarization states of the first tunable laser and the second tunable laser perpendicular to each other; A second beam splitter is used to split the first tunable laser, and a small part of the first tunable laser enters a first photodetector, and most of the first tunable laser enters a first polarization beam splitter prism; A third beam splitter is used to split the second tunable laser after the second tunable laser passes through a second mirror, and a small part of the second tunable laser enters a second photodetector, and most of the second tunable laser enters the first polarization beam splitter prism; The first photodetector and the second photodetector are used to measure the intensities of the first tunable laser and the second tunable laser entering the first photodetector and the second photodetector respectively; The first polarization beam splitter prism is used to combine the first tunable laser and the second tunable laser entering the first polarization beam splitter prism into a collinear laser beam; The second polarization beam splitter prism is used to separate the collinear laser beam after the collinear laser beam passes through a region above a sample surface and a plasmonic plume region, so as to obtain a combined beam of the first tunable laser and the second tunable laser after separation; The third photodetector and the fourth photodetector are used to measure the remaining intensities of the first tunable laser and the second tunable laser entering the third photodetector and the fourth photodetector respectively; The method further comprises a data processing device; The data processing device is used to obtain a ratio of two isotopes of a target element in the sample according to a difference between the remaining intensity of the first tunable laser measured by the third photodetector and the original intensity of the first tunable laser measured by the first photodetector, and a difference between the remaining intensity of the second tunable laser measured by the fourth photodetector and the original intensity of the second tunable laser measured by the second photodetector; The first tunable laser and the second tunable laser can obtain laser outputs with different line widths by using gratings with different ruling lines; wherein the line widths of the outputs are matched with spectral line widths and energy level hyperfine structures of the two isotopes of the target element in the sample.

2. The apparatus of claim 1, wherein, The first half-wave plate is arranged between the first tunable laser and the second beam splitter; The second beam splitter is arranged between the first half-wave plate and the first polarization beam splitter prism, and arranged between the first half-wave plate and the first photodetector.

3. The apparatus of claim 1, wherein, The second half-wave plate is arranged between the second tunable laser and the second mirror; The third beam splitter is arranged between the second mirror and the first polarization beam splitter prism, and arranged between the second mirror and the second photodetector.

4. A method for high-precision and rapid measurement of isotope ratio by dual-beam LAAS, suitable for the high-precision and rapid measurement device for isotope ratio by dual-beam LAAS according to any one of claims 1-3, characterized in that, The method comprises the following steps: A nanosecond pump laser is used to pump a first tunable laser and a second tunable laser with laser generated by the nanosecond pump laser through a first beam splitter and a first mirror respectively, so as to generate two tunable lasers, which are recorded as a first tunable laser and a second tunable laser respectively; The polarization states of the first tunable laser and the second tunable laser are perpendicular to each other by using the first half-wave plate and the second half-wave plate; then a small part of the first tunable laser enters the first photodetector after passing through the second beam splitter, so as to measure the intensity of the first tunable laser, and most of the first tunable laser enters the first polarization beam splitter prism; a small part of the second tunable laser enters the second photodetector after passing through the second mirror and the third beam splitter in turn, so as to measure the intensity of the second tunable laser, and most of the second tunable laser enters the first polarization beam splitter prism; The first polarization beam splitter prism combines the first tunable laser and the second tunable laser entering it into a collinear laser beam; the collinear laser beam passes through the plume region above the surface of the sample to be measured, and after the two wavelengths of laser are resonantly absorbed by two isotopes in the sample to be measured in the plume, the remaining laser is separated into the first tunable laser and the second tunable laser by the second polarization beam splitter prism again, and acts on the third photodetector and the fourth photodetector respectively to measure the pulse intensity; According to the difference between the original intensity and the remaining intensity of the first tunable laser measured by the third photodetector and the first photodetector, and the difference between the original intensity and the remaining intensity of the second tunable laser measured by the fourth photodetector and the second photodetector, the ratio of the two isotopes of the target element in the sample to be measured is obtained.

5. The method of claim 4, wherein, The line widths of the first tunable laser and the second tunable laser are controlled by selecting different grating lines in the first tunable laser and the second tunable laser.

6. The method of claim 4, wherein, The sample to be measured is ablated by the ablation laser output by the short pulse laser to generate a plume.

7. The method of claim 4, wherein, The line widths of the first tunable laser and the second tunable laser are different, and match the spectral line width of the two isotopes of the target element in the sample to be measured. The line widths of the first tunable laser and the second tunable laser are different, and match the spectral line width of the two isotopes of the target element in the sample to be measured.

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