A device and method for detecting isotopic abundance and ratio based on molecular emission spectrum

Abstract

The application relates to the technical field of isotope detection, in particular to an isotope abundance and ratio detection device and method based on molecular emission spectrum. The device comprises a computer and a long-pulse laser unit, an optical path transmission unit, an LED illumination focusing unit, a three-dimensional displacement table and a spectrometer connected with the computer. The existing viewpoint considers that long-pulse laser is not conducive to micro-area excitation and high-resolution spectrum acquisition due to its wide pulse width, and is less applied in isotope subtle spectral line difference identification. The application breaks through the molecular emission cascade mechanism, enhances the signal intensity, realizes the possibility of micro-area high-resolution isotope molecular detection, generates plasma by in-situ laser ablation, induces molecular emission spectrum, realizes rapid, accurate and real-time in-situ detection of the isotope abundance and ratio in the sample. The device has few optical elements, simple structure and convenient optical path adjustment, and is conducive to miniaturization and on-site application promotion.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of isotope detection, and particularly relates to an isotope abundance and ratio detection device and method based on molecular emission spectrum, which can realize in-situ, rapid and automatic detection of isotope abundance and ratio. BACKGROUND

[0002] Isotope abundance and ratio detection technology has important application value in many fields such as nuclear energy development, geological exploration, environmental monitoring and life science. Among them, different isotopes have slight differences in physical and chemical properties, which makes them have unique advantages in tracing analysis, age determination and nuclear reaction process monitoring. For example, in the nuclear fuel cycle system, accurate grasp of the isotope abundance of radioactive elements such as uranium or plutonium is the key to ensure the safety and efficiency of the reactor; in the analysis of geological samples, the ratio of different lead or strontium isotopes can be used to determine the mineral formation age and the cause of the environment; and in medical diagnosis and pharmacokinetic research, the abundance change of stable isotope markers can be used to monitor the metabolic pathway and drug absorption. Therefore, developing an analysis technology that can quickly, accurately and non-destructively detect the isotope abundance and ratio of materials has very important scientific significance and practical value for improving material tracking ability, strengthening process control, ensuring system safety and expanding the application field of isotopes.

[0003] In the current isotope detection, atomic absorption spectrum is a more commonly used technology, which is mainly used to distinguish the energy level structure changes caused by the nuclear mass difference of isotopes. Atomic absorption spectrum can accurately capture the absorption peak shift caused by the nuclear mass difference of isotopes by analyzing the linear spectrum generated by the electronic energy level transition of gaseous atoms or ions. The absorption peak shift of uranium-235 and uranium-238 is about 0.004 nm. This method has high resolution and sensitivity, and is suitable for detecting light element isotopes such as carbon-13 and carbon-12. However, this method also has significant limitations, including extremely narrow spectral lines, weak signal background, significant influence of stokes broadening, significant matrix interference and poor measurement repeatability. In particular, since the absorption spectral line width is usually greater than the spectral line shift between isotopes, the detector is required to have an ultra-high resolution capability of picometer (pm) level, which has high technical threshold and cost pressure in experimental implementation.

[0004] The current mainstream concept believes that molecular emission spectrum is difficult to distinguish the isotope shift caused by the nuclear mass difference due to its blurred band structure, serious energy level overlap, low signal-to-noise ratio in complex background and limited spectral resolution. Therefore, atomic absorption spectrum or mass spectrometry and other high-resolution analysis methods are more commonly used as a means of detecting isotope abundance and ratio.

[0005] However, mass spectrometry relies on high-precision mass analysis instruments to obtain the corresponding abundance information by separating and detecting each isotopic ion in the sample. Although mass spectrometry has high sensitivity and resolution, there are still many limitations in practical application. On the one hand, mass spectrometry usually requires complex sample pretreatment steps and cannot achieve in-situ detection, making it difficult to meet the demand for rapid and non-destructive measurement in industrial production. On the other hand, the traditional mass spectrometry process takes a long time and cannot be monitored in real time, making it difficult to provide timely feedback on dynamic processes. In addition, in the analysis of samples involving radioactive substances such as uranium, mass spectrometry often requires manual sampling operations, which not only is inefficient but also poses a high risk of radiation exposure to the operator, posing irreversible harm to the operator's health.

[0006] Therefore, developing a device and method capable of realizing in-situ, rapid, and automated detection of isotopic ratio and abundance has important application value for improving the efficiency and safety level of industrial production.

[0007] In addition, the traditional laser ablation atomic absorption spectroscopy has significant technical bottlenecks in hydrogen / deuterium isotope analysis. On the one hand, in the laser-induced plume (Laser-Induced Plume) formed under atmospheric pressure, the spectral line Stark broadening phenomenon is extremely obvious. On the other hand, the laser-induced plasma (Laser-Induced Plasma, LIP) of water samples usually has extremely high electron density, which significantly exacerbates the degree of spectral line Stark broadening. In particular, the H a and D a emission spectral line Stark broadening coefficient itself is at the highest level, resulting in further broadening of the spectral line and making spectral analysis more difficult. Although delaying the signal acquisition time can inhibit the broadening to some extent, the detection signal-to-noise ratio is significantly reduced due to the rapid decay of the emission intensity over time, so the traditional laser ablation atomic absorption spectroscopy cannot meet the requirements of high-precision water D / H isotope abundance measurement. In addition, the isotopic shift in the atomic absorption spectral line of hydrogen is extremely small, and the shift between H a and D a is only about 18 pm, which is close to the resolution limit of most conventional spectrometers, making it a challenging task to accurately distinguish between H and D abundance.

[0008] The above information disclosed in the background technology is only used to increase the understanding of the background technology of the present application, and should not be regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art. SUMMARY

[0009] Although the current mainstream concept considers that the molecular emission spectrum is not used as the mainstream technical means for detecting isotopic abundance and ratio due to its band structure blur, serious energy level overlap, low signal-to-noise ratio in a complex background and limited spectral line resolution, and more atomic absorption spectroscopy or mass spectrometry which needs extremely high resolution detection is adopted. However, the application firstly proposes to apply long-pulse laser-induced molecular emission spectrum to the field of isotopic quantitative detection, breaks through the traditional technical cognition of 'weak molecular spectrum signal, strong background interference and difficult to extract with high resolution', and constructs an excitation-collection integrated detection platform with high synergy and integration capability.

[0010] The application significantly improves the spectral line intensity through the cascade amplification mechanism of molecular emission, prolongs the plasma lifetime and stabilizes the emission window by using a high-pressure inert gas environment, realizes background suppression and baseline correction by combining the delay gate acquisition strategy and the AsLS+SNIP composite algorithm, so that the weak isotopic shift signal can be clearly identified in a complex environment. Especially for OH / OD and CN and other heteronuclear diatomic molecules, the vibration-rotation energy level structure is highly sensitive to the reduced mass, and the molecular band head displacement can be more than 10 times that of the atomic spectral line. The application can realize the separation of isotopic molecular band heads with a precision of 0.015 nm through the spectrometer system, and realize the in-situ automatic detection of D / H, 13C / 12C and other isotopic ratios in water samples or organic samples without derivatization treatment.

[0011] Therefore, the application not only challenges the traditional view that'molecular spectrum cannot be used for high-precision isotopic analysis', but also realizes the synergistic breakthrough of signal enhancement, background weakening and significant improvement of analysis precision through multiple innovations in light source control, signal acquisition, spectral processing and system structure, fully embodying the originality and practical value of the technical solution.

[0012] In summary, in order to solve the problems existing in the prior art, the application overcomes the technical bias and provides an isotopic abundance and ratio high-precision detection device and method based on long-pulse laser ablation molecular emission spectrum. Compared with the short-pulse laser commonly used in the prior art, the application uses a long-pulse laser which is not commonly used in the field, realizes in-situ, rapid and automatic detection of isotopic abundance and ratio by ablation of molecular emission spectrum. Compared with the existing device, the application has lower cost, stronger repeatability, higher signal-to-noise ratio and better data processing capability, and has the potential to be popularized to practical environmental monitoring and online detection applications.

[0013] The technical scheme of the application is as follows:

[0014] A kind of isotope abundance and ratio detection device based on molecular emission spectrum, including single long pulse laser unit, for emitting laser pulse with pulse width ≥100ns, frequency 1~10HZ, energy 0~120mJ, to excite the sample to be measured to generate plasma.

[0015] Optical path transmission unit, for receiving long pulse laser and being reflected and focused to the surface of sample to be measured by mirror group, first beam splitter, dichroic mirror and microscope objective, while introducing plasma emission light into detection light path.LED illumination focusing unit, including LED white light illumination, reflector and monitoring camera, for providing auxiliary white light illumination under microscope objective and observing focal plane in real time.

[0016] Three-dimensional displacement table, electrically connected with computer, for positioning detection point in X / Y plane and realizing automatic or manual focusing in Z direction.

[0017] Sealed sample cabin unit, including sealed gas cabin main body, optical window, gas inlet and outlet and pressure control system, for maintaining high-pressure inert gas environment in the region of sample to be measured.

[0018] Spectrometer, including collimating mirror, focusing lens, plane grating, grating driver, wavelength display meter and ICCD (enhanced charge-coupled device camera), EMCCD (electron multiplying CCD), supporting adjustable parameters such as external trigger, delay, gate width and gain, for molecular spectral light splitting and detection.

[0019] Computer, connected with long pulse laser unit, optical path transmission unit, LED illumination focusing unit, three-dimensional displacement table and spectrometer, for controlling emission timing and parameters of long pulse laser; driving LED illumination and three-dimensional displacement table to realize focusing and sample point switching; adjusting central wavelength of spectrometer and ICCD gate parameter and triggering spectrum acquisition; carrying out baseline correction, background removal and multi-peak fitting on acquired molecular spectrum, and calculating isotope abundance and ratio of sample to be measured.

[0020] Further, the long pulse laser unit includes:

[0021] Pump cavity, for providing laser medium pumping energy and realizing population inversion.

[0022] Acousto-optic Q-switching cavity, containing transducer, power supply, acousto-optic medium, sound absorbing material and cooling system, for realizing Q-switching instantaneous release of laser by acousto-optic diffraction.

[0023] Laser controller and supporting software, for adjusting pump source driving, Q-switch triggering and laser output parameters, and communicating with computer.

[0024] Further, the mirror group comprises 6 mirrors, the long pulse laser unit emits laser light, which passes through the lifting light path composed of two mirrors to reach the two mirrors limited by the cage structure, the cage structure keeps horizontal; then passes through the lifting light path composed of two mirrors to the beam splitter, one beam of light irradiates on the PIN tube, and one beam of light transmits through the dichroic mirror and is focused on the surface of the sample to be measured by the microscope objective.

[0025] Further, the first beam splitter is placed behind the last mirror, the first beam splitter uses the reflection and transmission characteristics of the optical film to divide the incident light into two parts, when the light beam passes through the first beam splitter, part of the light is reflected, and the other part of the light transmits through the first beam splitter, the transmitted light irradiates on the PIN tube, and the reflected light is incident to the dichroic mirror.

[0026] The dichroic mirror is arranged below the first beam splitter, and the dichroic mirror can separate the excitation laser light from the plasma emission light.

[0027] The mirror is detachably arranged below the dichroic mirror, and the mirror is used for reflecting the light source emitted by the LED light source to realize imaging and focusing; in the case of not focusing, the operator can remove the mirror, and the laser light passing through the dichroic mirror can directly reach the microscope objective; the long pulse laser light reaching the microscope objective is focused, the sample to be measured is excited to generate plasma, and after the mirror is installed, the LED illumination focusing unit can generate imaging effect, and the molecular signal light generated by the plasma can be collected and coupled into the optical fiber for light splitting detection.

[0028] Further, the spectrometer comprises a PIN tube trigger circuit, the PIN tube receives the laser pulse transmitted by the first beam splitter and outputs a trigger signal to realize ICCD external trigger acquisition, the delay is set to 2-50 μs, and the gate width is set to 20-150 μs.

[0029] Further, the pressure control system of the sealed sample cabin unit comprises a pressure sensor, an adjusting valve and a safety alarm device, which are used for real-time monitoring and keeping the inert gas pressure in the preset range of 101 kPa±1 kPa.

[0030] Further, the computer-callable molecular spectrum fitting software loads the rotational-vibrational constant and the spectrum line list, automatically completes the multi-spectrum peak fitting and outputs the isotopic abundance and ratio.

[0031] An isotopic abundance and ratio detection method based on molecular emission spectrum, the method comprises an excitation method and a detection method.

[0032] The excitation method comprises:

[0033] The sample to be measured is placed in the sealed gas cabin filled with high-pressure inert gas;

[0034] The mobile displacement table is used for focusing;

[0035] The long pulse laser is turned on, focused on the sample surface through the optical path to generate plasma, and the plasma emits molecular spectrum after several microseconds;

[0036] The detection method comprises:

[0037] The molecular spectrum signal emitted by the plasma is reflected into the optical fiber through the dichroic mirror;

[0038] The optical fiber couples the signal light into the spectrometer, and under the triggering of the PIN tube, the spectrometer starts to work to collect the signal spectrum;

[0039] The collected data is subjected to baseline correction and background removal;

[0040] The processed data is subjected to molecular spectrum fitting to analyze the isotopic abundance and ratio of the sample to be tested.

[0041] Specifically, the method comprises the following steps:

[0042] (1) Sample placement: placing the sample particles enriched with isotopes in the sealed sample chamber unit, and adjusting the inert pressure to 101 kPa ± 1 kPa;

[0043] (2) Microscopic focusing: turn on the LED white light illumination, drive the three-dimensional displacement table to make the sample surface coincide with the focal plane of the microscopic objective lens;

[0044] (3) Plasma excitation: trigger the long pulse laser unit according to the set frequency and energy, focus on the sample surface through the optical path transmission unit, and generate plasma;

[0045] (4) Spectrum collection: the plasma starts to emit molecular spectrum 2-15 μs after excitation, the signal is reflected and coupled into the optical fiber through the dichroic mirror, and the wavelength in the spectrometer is adjusted and collected by the ICCD according to the gate width of 30-150 μs under the triggering of the PIN tube;

[0046] (5) Data processing: Asymmetric Least Squares (AsLS) and Statistically-Sensitive Nonlinear Iterative Peak (SNIP) algorithm are applied to the original spectrum to correct baseline and remove background, and then the displacement of the isotopic molecular band head is analyzed by multi-peak fitting. Specifically, the characteristic peaks of the molecules in the molecular emission spectrum in the application, atomic peaks, continuous background radiation (from the bremsstrahlung or recombination radiation of the plasma) and instrument noise. The baseline drift (caused by plasma temperature fluctuations, instrument response instability, etc.) will mask weak molecular peaks and affect the accurate identification of peak position and peak intensity. The core idea of AsLS algorithm is to dynamically adjust the smoothing degree by least squares fitting combined with adaptive regularization: strong smoothing is used in the baseline area (no peak or weak peak) to fit the baseline; weak smoothing is used in the characteristic peak area (signal mutation) to retain the details of the peak (such as peak position, half-width, intensity). The core role of AsLS algorithm is to adaptively fit the baseline and remove the drift, and retain the original form of the molecular characteristic peak. After removing the baseline, there is still structured background (such as continuous radiation of matrix elements, wide peak interference of molecular clusters), which may overlap with the target molecular peak, resulting in peak identification and integration error. The core idea of SNIP algorithm is that the algorithm will calculate the local minimum value of the spectrum in different windows multiple times, and the signal higher than the local minimum value is regarded as "part of the peak", and the signal lower than or equal to the local minimum value is regarded as "background", and finally the true peak is retained and the smooth background is deducted. SNIP algorithm is an efficient background deduction method, especially suitable for spectral processing in complex background.

[0047] (6) Isotope calculation: the molecular spectrum fitting software (Pgopher molecular spectrum software) is called, the molecular constant and the spectrum line list are loaded, and the isotope abundance and ratio of the sample to be measured are automatically fitted and output.

[0048] Further, the AsLS and SNIP algorithms can be used alone or in combination, and the residual baseline can be further removed by continuous wavelet transform and interpolation method.

[0049] Further, the central wavelength of the spectrometer is in the range of 190-800 nm, which is scanned by a stepping motor and a sine arm driving grating, and the wavelength repeatability is ±0.005 nm.

[0050] The application has the following beneficial effects:

[0051] 1. Existing viewpoints suggest that long-pulse lasers, due to their wide pulse width, are unfavorable for micro-area excitation and high-resolution spectral acquisition, thus limiting their application in identifying subtle spectral differences in isotopes. This invention, however, innovatively enhances signal intensity through a molecular emission cascade mechanism, enabling high-resolution micro-area isotope molecular detection. By generating plasma through in-situ laser ablation and inducing molecular emission spectra, rapid, accurate, and real-time in-situ detection of isotope abundance and ratios in samples is achieved. This detection scheme combines the deep excitation effect of long-pulse lasers on local sample regions with the characteristic emission behavior of molecular spectra in the later stages of the reaction, significantly enhancing the intensity and stability of the molecular spectral signal. This provides a feasible and widely applicable technical path for efficient isotope detection in industrial applications.

[0052] 2. This invention achieves isotope detection through molecular emission spectroscopy, utilizing the large displacement and high-intensity characteristic spectral lines resulting from intermolecular vibrational and rotational transitions. Compared to atomic absorption spectroscopy, the signal is enhanced by more than 30 times, and the isotope shift is significantly increased to more than ten times that of atomic spectroscopy. Detection targets such as OH and OD groups are naturally formed during laser ablation, and their spectral lines directly reflect the D / H ratio in the sample, eliminating the need for any derivatization pretreatment steps, significantly simplifying the experimental procedure and improving data reliability.

[0053] 3. This invention employs a single long-pulse laser to simultaneously perform excitation and detection, ensuring high system coordination and timing consistency, thereby improving experimental reproducibility and integration. Its pulse width is highly matched to the timescale of molecular bond breaking and reaction formation, which is beneficial for the continuous generation of excited-state molecules and the formation of an emission cascade mechanism. Furthermore, the equipment is low-cost, highly versatile, and applicable to the vast majority of experimental platforms.

[0054] 4. In this invention, excitation and detection occur simultaneously from the same source, significantly simplifying the optical path system, reducing sources of error, ensuring experimental repeatability and operational efficiency, and improving data reliability. The entire device has a simple structure, requires a significantly reduced number of optical components, and is easy to adjust, which is conducive to equipment miniaturization and field application.

[0055] 5. The timing control strategy in this invention is based on real-time laser emission signal feedback. Through the beam splitting-PIN detection-electrical signal synchronization-spectrometer delayed start mechanism, it automatically completes the precise alignment of the acquisition time window with the plasma emission process, which greatly improves data accuracy and repeatability.

[0056] 6. In this invention, the microscope objective not only undertakes the task of focusing, but also integrates multiple functions such as image imaging, sample micro-area capture, autofocus and signal enhancement. Combined with LED and CMOS camera, it realizes real-time control, image feedback and precise data acquisition during the experiment.

[0057] 7、The three-dimensional displacement platform of the present application can realize active focusing control in the vertical direction, and can automatically adjust the sample height in cooperation with the laser displacement feedback system, so that the focal point is always consistent during the surface scanning process, and signal deviation is avoided. The microscope objective has high numerical aperture and achromatic characteristics, which can realize high-precision laser focusing, and can also complete complex operations such as sample image imaging and micro-area spectrum acquisition, and is a core optical element for realizing spatial resolution precision spectrum measurement. Through the triple cooperation system of the microscope objective+LED+camera, focusing adjustment can be performed through automatic imaging, which not only improves the signal strength, but also significantly shortens the focusing time and improves the experimental efficiency.

[0058] 8、The present application supports automatic export and batch processing of spectral data, so that users can freely perform baseline fitting, background subtraction, spectral line enhancement and other operations according to specific analysis requirements, greatly improving data accuracy and research depth. The embedded time sequence control mechanism avoids human setting errors and improves system operation consistency. The laser emission process triggers the PIN detector through a light splitting path, and the signal synchronously starts the spectrometer delay acquisition, ensuring accurate alignment of data acquisition during the plasma emission stage, effectively enhancing the signal-to-noise ratio and suppressing background interference

[0059] 9、The whole detection process of the present application only needs 3 minutes from placing the sample to be tested to outputting the result, which is significantly better than the time-consuming of more than 10 minutes of the existing device. In terms of accuracy and performance, the present application fills 101kPa of argon or helium, prolongs the plasma lifetime to 50-100us, enhances the molecular emission intensity by 3 times, and the signal-to-noise ratio reaches 200:1, which is much higher than the 80:1 of other commonly used measurement systems. The long pulse laser has a pulse width of ≥100ns, which provides sufficient energy to ablate the sample, while avoiding the transient instability of the femtosecond laser. Delaying 2-5us to collect molecular spectra effectively avoids atomic line interference, and combined with the spectrometer, the isotopic abundance detection limit is as low as 0.1%, which is better than the 0.5-1% of the existing commonly used measurement system. The repeatability error of the present application is less than 2%, which meets the industrial high-precision requirements.

[0060] In summary: the present application is significantly better than the existing device in terms of system integration, experimental reliability, spectral signal quality and operation automation, has lower cost, stronger repeatability, higher signal-to-noise ratio and better data processing capability, and has the potential to be popularized to practical environmental monitoring and online detection applications. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 is a schematic diagram of the difference between the long pulse laser and the short pulse laser of the present application.

[0062] Figure 2 is a schematic diagram of the whole structure of the device of the present application.

[0063] Figure 3 is a schematic diagram of the whole structure of the device of the present application.Figure 2 Structure diagram of the middle reflecting mirror group.

[0064] Figure 4 Structure diagram of the three-dimensional displacement stage in the present application.

[0065] Figure 5 Structure diagram of the sealed sample chamber unit in the present application.

[0066] Figure 6 Figure 2 Structure diagram of the spectrometer in the present application.

[0067] Figure 7 Timing control diagram of the device in the present application.

[0068] Figure 8 Flow chart of the method in the present application.

[0069] Figure 9 H / D isotope molecular spectrum experimental result diagram.

[0070] Figure 10 H / D isotope molecular spectrum absolute abundance and ratio molecular spectrum fitting result diagram.

[0071] Figure 11 d 3 Πg→a 3 Πμ(1-0)CC isotope molecular spectrum experimental result diagram.

[0072] Figure 12 OH molecular spectrum experimental result diagram in inert gas environment.

[0073] Figure 13 OH molecular spectrum experimental result diagram in air environment.

[0074] Figure 14 B 2 Σ+→X 2 Σ+(0-1)CN isotope molecular spectrum experimental result diagram.

[0075] ​In the figure, 1, long pulse laser; 2, mirror group; 21, mirror I; 22, mirror II; 23, mirror III; 24, mirror IV; 25, mirror V; 26, mirror VI; 3, first beam splitter; 4, dichroic mirror; 5, microscope objective; 6, LED white light illumination; 7, reflector; 8, camera; 9, three-dimensional displacement table; 91, X-axis drive unit; 92, Y-axis drive unit; 93, Z-axis drive unit; 94, sample table; 10, spectrometer; 101, plane grating; 102, grating driver; 103, focusing lens; 104, wavelength display meter; 105, ICCD; 106, spectral mirror; 107, EMCCD; 108, collimating mirror; 109, slit; 11, PIN tube; 12, sealed sample cabin unit; 121, sealed gas cabin body; 122, optical window; 123, gas inlet and outlet; 13, sample to be measured; 14, inert gas tank; 15, computer. DETAILED DESCRIPTION

[0076] To make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application but not all the embodiments. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0077] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents the preferred embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work under the premise that the scope of protection of the present application.

[0078] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0079] In the description of the application, it needs to be explained that the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship when the product of the application is usually placed, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application. In addition, the terms "first", "second", "third" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance. In the description of the application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0080] In the description of the application, it also needs to be explained that, unless otherwise explicitly specified and limited, the terms "provided", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0081] In the present application, unless otherwise explicitly specified and limited, "on" or "under" of the first feature to the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, "on", "above" and "above" of the first feature to the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. "Below", "below" and "below" of the first feature to the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0082] The embodiments of the application are described in detail below, and examples of the embodiments are shown in the drawings, wherein the same or similar reference numerals represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the application, and cannot be understood as a limitation on the application.

[0083] Example 1: Isotope abundance and ratio detection device and method based on molecular emission spectrum

[0084] As Figures 2-8As shown, the present application provides a kind of molecular emission spectrum based on isotope abundance and ratio detection device and method, working principle is based on long pulse laser ablation sample, generates plasma emission molecular spectrum, and can accurately distinguish the isotope displacement of molecular emission band head in combination with the resolution of 0.015nm spectrometer 10.It is completed by the cooperation of multiple units of device, including: long pulse laser 1, optical transmission unit, LED illumination focusing unit, three-dimensional displacement table 9, sealed sample cabin unit 12, spectrometer 10 and computer 15.

[0085] Long pulse laser 1 is used to emit long pulse width low frequency 1064nm laser, first utilize the pump light emitted by semiconductor laser diode (LD) to pump from the side of YAG crystal.Then, acoustic-optic Q-switching is carried out, at the beginning, the incident laser beam diffracts in the acoustic-optic crystal, and the laser cannot oscillate, and a large number of inversion particle numbers are accumulated in the laser medium under the excitation of pump light.When accumulated to a certain extent, the accumulated inversion particle numbers are converted into laser energy through stimulated radiation process in a very short time, forming high-intensity short pulse output.With the release of output laser pulse, the inversion particle number rapidly decreases, and the laser pulse gradually attenuates until the oscillation stops, waiting for the next pump and Q-switching cycle.The adjustable laser frequency is 1-10HZ, and the laser energy is 0-120mJ.

[0086] Optical transmission unit is used for transmitting long pulse laser, long pulse is incident to the first beam splitter 3 through the mirror group, and the reflected long pulse laser transmits through the dichroic mirror 4, and the transmitted laser is focused to the surface of the sample to be measured 13 by the microscope objective 5.

[0087] LED illumination focusing unit and three-dimensional displacement table 9, LED light source emits LED light through reflector 7, and the reflected LED light shines on the surface of the sample to be measured 13, and the projected light source reaches the camera 8 to observe the focusing condition, and the focusing process is realized by moving the displacement table to focus the laser.

[0088] Spectrometer 10, according to the detection of different isotopes, the motor drives the grating to rotate to the required detection center wavelength, and the operator can determine the center wavelength after rotating the grating through wavelength display meter 104 whether it is consistent with the required center wavelength of the experiment, and the spectrometer is matched with Andor original factory's ICCD 105 and EMCCD 107, here the operator selects to use ICCD 105 and EMCCD 107 by rotating the mirror inside the spectrometer, and selects ICCD 105 with ultrafast time resolution when detecting isotopes.Long pulse transmits through the first beam splitter 3 and reaches the PIN tube 11, and the PIN tube 11 is connected with the spectrometer 10, and the PIN tube 11 triggers the spectrometer 10 to collect molecular spectrum when there is laser.

[0089] The sealed sample chamber unit 12 is used to place the sample 13 to be tested and to fill in high-pressure inert gas to generate an inert gas environment.

[0090] The computer 15 is connected with the long pulse laser 1, the spectrometer 10 and the displacement table, and is used to adjust the parameters of the laser, to realize manual and automatic sample focusing, and to set the acquisition parameters of the spectrometer 10.

[0091] In this embodiment, the long pulse width low repetition rate laser is combined with the high-pressure inert gas sample environment and the high-resolution spectrometer 10, so that the excitation and detection analysis of the molecular spectrum are closely cooperated. The long pulse laser can fully ablate the sample and improve the signal of the molecular spectrum. The high-pressure inert gas environment enhances the lifetime and temperature of the plasma, reduces the air interference, improves the stability of the molecular signal, and the spectrometer 10 with a resolution of 0.015 nm can accurately distinguish the isotopic shift of the molecular emission band head.

[0092] Specifically, an isotopic abundance and ratio detection device based on molecular emission spectrum comprises:

[0093] The single long pulse laser 1 is used to emit laser pulses with a pulse width of ≥100 ns, a frequency of 1-10 Hz and an energy of 0-120 mJ, so as to excite the sample 13 to be tested to generate plasma.

[0094] The long pulse laser 1 comprises a pumping area, a Q-switching area, a controller area and a software area. The pumping area provides pumping energy to pump the ground state particles in the laser medium to the upper energy level, forms particle number inversion, and amplifies the initial laser by stimulated emission. The high pulse width low energy laser is narrowed in pulse width by the Q-switching unit to generate high energy laser with a pulse width of 50 mJ or more. The control area can provide power supply for the laser, can select the Q-switching mode of the laser, and is connected with the computer 15, so that some parameters of the laser can be controlled by using software.

[0095] The long pulse laser 1 refers to a laser system with an output pulse duration in the range of tens of nanoseconds to several microseconds (10 -8 s-10 -6 s). Figure 1 Compared with the short pulse, as shown in the figure, the long pulse laser has lower peak power, longer pulse width and wider plasma cooling window, which is beneficial to the generation of atomic isomers and the emission of stable molecular spectrum, and is suitable for ICCD 105 gating with a wide gate width (μs level) to suppress the initial continuous spectrum and improve the signal-to-noise ratio of the molecular spectrum.

[0096] The embodiment adopts a single long pulse laser to simultaneously complete excitation and detection, ensures high coordination and consistent timing of the system, and improves experimental reproducibility and integration. A second laser and a signal generator do not need to be added to achieve the effect of detection as in other existing devices.

[0097] The optical path transmission unit is used for receiving long pulse laser and reflecting and focusing the laser to the surface of the sample 13 to be detected through the multi-faceted mirror group 2, the first beam splitter 3, the dichroic mirror 4 and the microscope objective 5, and introducing the plasma emission light into the detection light path.

[0098] Specifically, the optical path transmission unit comprises the mirror group 2, the dichroic mirror 4, the microscope objective 5, the first beam splitter 3 and the PIN tube 11.

[0099] The optical path of the existing device for isotope measurement is relatively complex, and about 20 optical lenses are used, and even some use a double-axis optical path, which makes the requirements for the coordinated work of the system very harsh, and the system needs to be adjusted for a short time to achieve the measurement requirement. It cannot meet the requirement of long-time repeated work, and the optical path in the existing device is only an optical path, which can only realize the function of the ship body laser or signal light. The optical path of the present application is very simple, and only has 9 optical lenses, and the optical path of the present application can realize the control of the spectrometer 10 and the focusing unit, and realize the coordinated work of light, machine and electricity.

[0100] The mirror group 2 comprises six mirrors. The laser emitted by the laser is transmitted through the lifting optical path composed of two mirrors to the two mirrors limited by the cage structure, and the cage structure is kept horizontal. Then the laser is incident to the first beam splitter 3 through the lifting optical path composed of two mirrors. The mirror group 2 mainly realizes the transmission of the laser.

[0101] Specifically, as shown in Figure 3 The mirror group 2 comprises mirror I 21, mirror II 22, mirror III 23, mirror IV 24, mirror V 25 and mirror VI 26. The laser enters through the mirror I 21, then enters the mirror II 22, and then changes the optical path through the mirror III 23, and then enters the mirror VI 26 through the mirror IV 24 and the mirror V 25, and then is emitted from the mirror VI 26 to enter the first beam splitter 3.

[0102] The first beam splitter 3 is placed behind the mirror 26, and the first beam splitter 3 separates the incident light into two parts by using the reflection and transmission characteristics of the optical film, when the light beam passes through the beam splitter, one part of the light is reflected, and the other part of the light transmits through the beam splitter. The long pulse laser light reaching the first beam splitter 3 is divided into two beams, one of which irradiates the PIN tube 11, at this time, the PIN tube 11 is triggered to output an electrical signal to trigger the spectrometer 10, and the other beam is incident on the dichroic mirror 4.

[0103] The dichroic mirror 4 is arranged below the first beam splitter 3, and the dichroic mirror 4 can separate the laser light used to excite the plasma from the plasma emission light, the dichroic mirror 4 has high transmittance to 1064nm laser light, ensuring that the laser light can pass through and focus on the surface of the sample 13 to be measured efficiently, and the plasma emission spectrum signal usually contains multiple wavelengths (such as ultraviolet to visible light range), and the dichroic mirror 4 can reflect these lights.

[0104] The laser light passing through the dichroic mirror 4 can optionally pass through the mirror 7, because the mirror 7 can be freely removed and inserted, the main function of the mirror 7 is to reflect and transmit the light emitted by the LED light source to realize imaging and focusing. In the case of not focusing, the operator can remove the mirror 7, and the laser light passing through the dichroic mirror 4 can directly reach the microscope objective 5.

[0105] The long pulse laser light reaching the microscope objective 5 is focused, and the sample 13 to be measured is excited to generate plasma, which can be combined with the LED illumination focusing unit to produce imaging effect, and the molecular signal light generated by the plasma can be collected and coupled into the optical fiber for spectroscopic detection.

[0106] The PIN tube 11 is placed behind the first beam splitter 3, and receives the laser light emitted by the long pulse laser 1, and the photoelectric conversion outputs an electrical signal to trigger the high-precision spectrometer 10.

[0107] The present application adopts a coaxial reverse collection mechanism, and excitation and signal collection share the same light path, so that the structure is simplified and the light energy utilization is high.

[0108] The LED illumination focusing unit is used to generate white light to assist the microscope in focusing, and includes the LED white light illumination 6, the detachable mirror 7 and the monitoring camera 8, which are used to provide auxiliary white light illumination under the microscope objective 5 and observe the focal plane in real time.

[0109] Specifically, the LED illumination focusing unit includes: the mirror 7, the LED white light illumination 6 and the monitoring camera 8.

[0110] The white light generated by the LED white light illumination 6 is focused by the microscope objective 5 through the reflector 7. The sample 13 to be tested is moved up and down by the three-dimensional displacement stage 9, and the surface of the sample 13 to be tested is placed on the focal plane of the microscope objective 5. The focusing effect and situation can be observed by the monitoring camera 8. When the clearest picture appears, it means that the focusing is successful.

[0111] like Figure 4 As shown, a three-dimensional displacement stage 9 is used to select different sample points by moving the stage in three dimensions. It is electrically connected to a computer 15 and is used to locate the detection point in the X / Y plane and achieve automatic or manual focusing in the Z direction. It includes an X-axis drive unit 91, a Y-axis drive unit 92 mounted on the X-axis drive unit 91, and a Z-axis drive unit 93 mounted on the Y-axis drive unit 92. It also includes a sample stage 94, which is mounted on the Z-axis drive unit 93.

[0112] like Figure 5 As shown, the sealed sample chamber unit 12 is used to fill with high-pressure inert gas at 101 kPa and to place samples; it includes a sealed chamber body 121, an optical window 122, a gas inlet and outlet 123, and a pressure control system for maintaining a high-pressure inert gas environment in the sample area. Helium and argon are preferred inert gases.

[0113] The sealed gas chamber body 121 is a sealed container made of a material with good optical transmittance and mechanical strength (such as fused silica) to contain high-pressure inert gas. The inert gas pressure is within a preset range of 101 kPa ± 1 kPa.

[0114] High-pressure inert gases effectively suppress the rapid expansion and cooling of plasma, extending its lifetime and providing more time for molecular species formation and emission, thus facilitating the capture of more complete molecular emission spectra. Secondly, the chemical stability of inert gases ensures that they will not chemically react with the sample or plasma in a high-temperature plasma environment, avoiding potential interference and improving measurement accuracy. Furthermore, high-pressure inert gases can increase plasma density and temperature, enhance emission intensity, and improve the signal-to-noise ratio, thereby increasing measurement sensitivity and precision. For example, in some experiments, using a high-pressure argon environment can extend the plasma lifetime to tens of microseconds, significantly improving the detection efficiency of molecular spectra. Using high-pressure inert gases as the environmental medium for molecular spectroscopy experiments not only optimizes plasma characteristics and enhances molecular emission signals but also improves measurement accuracy and sensitivity.

[0115] The gas inlet and outlet 123 is used to inject and discharge gas into the sealed gas chamber body 121. The inlet is connected to a high-pressure gas cylinder, and the outlet is connected to a vacuum pump.

[0116] The pressure control system unit includes pressure sensors, valves, and pressure regulators, which are used to precisely control the air pressure inside the air chamber. When the air pressure is too high, an alarm can be set to prevent accidents.

[0117] The optical window 122 is made of a material with good optical transmittance and resistance to laser damage (such as fused silica) and is used for the entry of the laser beam and the output of the spectral signal.

[0118] like Figure 6 As shown, the spectrometer 10 includes a collimating lens 108, a focusing lens 103, a planar grating 101, a grating driver 102 (which can pull the grating to rotate), and an Andor ICCD 105. It supports adjustable parameters such as external triggering, delay, gate width, and gain, and is used for molecular spectroscopy and detection.

[0119] In this embodiment, the spectrometer 10 is a Model 209 monochromator, including: an optical system, an instrument base, a grating, a wavelength driver, an ICCD105 detector, and an EMCCD107 detector. The data acquisition section uses an ICCD105 device, which has high sensitivity, strong background suppression capability, and optical signal amplification function. It can accurately capture weak emission spectral lines and is suitable for high dynamic range detection under complex background conditions.

[0120] The optical system includes: entrance and exit slits 109, collimating lens 108, focusing lens 103, and a micrometer (located inside the spectrometer; during grating rotation, the focusing lens is driven to perform micrometer-level linear translation to dynamically compensate for focus shift caused by grating wavefront error. This compensation mechanism ensures that the selected center wavelength is always accurately focused on the ICCD detection surface, effectively ensuring that the spectrometer maintains its nominal spectral resolution performance throughout the entire scanning band). The collimating lens 108 is placed at the entrance slit 109. The height and width of the entrance slit 109 can be adjusted to adjust the light flux entering the spectrometer 10, while also filtering out most of the background light to avoid interference. The collimating lens 108 collimates the molecular spectral signal light generated by the sample passing through the slit 109. The focusing lens 103 focuses the monochromatic light separated by the grating onto the camera 8 for detection. The micrometer is used to precisely adjust the position of the focusing lens 103 to achieve precise focus adjustment.

[0121] The instrument base is a cast aluminum base with a flattened top to accommodate the mirror, grating, and precision lead wire assembly. A separate casting is mounted on the base to support the grating assembly and camera accessories.

[0122] The grating is a 1200 line / mm Snap-In plane grating 101, the surface area of the grating is 110mm*110mm, the line area is 102mm*102mm, the resolution of the grating can reach 0.015nm, and the dispersion power is 0.62nm / mm.

[0123] The ICCD 105 detector includes an image intensifier, a CCD sensor, a gating system, and a refrigeration system. The photocathode converts incident photons into electrons, the MCP amplifies the electrons, the phosphor screen converts the electrons back into visible light, the enhanced light signal is received by the CCD sensor, the CCD is used to receive the light signal output by the image intensifier and convert it into an electrical signal for reading and processing. The gating system has a low jitter and short insertion delay circuit, which can accurately control the gating time and delay of the image intensifier, ensure synchronization with external hardware, connect the PIN tube 11 with the gating system, and control the collection of the spectrum when the plasma occurs molecular spectrum, and filter out most of the background and noise.

[0124] The computer 15 is electrically connected with the long pulse laser 1, the optical path transmission unit, the LED illumination focusing unit, the three-dimensional displacement stage 9, and the spectrometer 10, and is used for: controlling the emission timing and parameters of the long pulse laser 1; driving the LED illumination and the three-dimensional displacement stage 9 to realize focusing and sample point switching; adjusting the center wavelength of the spectrometer 10 and the gating parameters of the ICCD 105 and triggering spectrum acquisition; performing baseline correction, background removal and multi-peak fitting on the collected molecular spectrum, and calculating the isotopic abundance and ratio of the sample 13 to be measured.

[0125] The laser emitted by the long pulse laser 1 and the white light emitted by the LED illumination focusing unit are both focused on the surface of the sample 13 to be measured.

[0126] Specifically, the computer 15 unit is connected with the controller of the long pulse laser 1, and the output frequency of the laser can be adjusted as needed (1-10HZ), the power supply current of the laser (1-190A) and the power supply pulse width (230μs-300μs) are adjusted, so that the energy adjustment range of the laser is 0-120mJ.

[0127] The computer 15 unit is connected with the LED illumination focusing unit and the circuit displacement stage control unit, and the sample surface can be observed through the camera 8. The clearer the sample surface is, the better the focusing effect is. According to the picture of the camera 8, the three-dimensional displacement stage 9 can be controlled through the computer 15 to realize focusing in the Z-axis direction and sample point selection in the X, Y plane.

[0128] Optionally, the long pulse laser 1 emits 1064nm laser.

[0129] The dichroic mirror 4 transmits 1064nm laser and reflects other wavelength signal light, the optical axis of the dichroic mirror 4 and the optical axis of the beam splitter are at an angle of 45° with the propagation path of the laser beam.

[0130] The wavelength range of the spectrometer 10 can be selected as 185nm to 1.3μm, the wavelength range of the focal plane is 31nm, the wavelength repeatability is ±0.05nm, and the wavelength repeatability is ±0.005nm.

[0131] The control module of the system is connected with the computer 15 and the three-dimensional displacement table 9, and the operator can select a suitable detection point by matching the LED illumination focusing unit and the microscope objective 5 in the software, and manually focus by moving the displacement table up and down in the software. The circuit board is connected with the LED light source, the monitoring camera 8 and the laser displacement device, and the other end is connected with the computer 15, so that the operator can turn on and off the LED light source and the monitoring camera 8 in the software to realize visual focusing at any time. When performing isotopic detection on the whole surface, the operator can manually focus at the starting point, record the Z-axis height of the starting point, and then pre-scan to automatically move the displacement table to scan the whole surface of the laser displacement device. They will feed back the Z-axis height of each point to the circuit board, so that when performing real surface detection, the displacement table will read the Z-axis height of each point stored in the circuit board to automatically move up and down for automatic focusing. All the functions of the control are integrated into a software.

[0132] The timing control module of the system is as shown in Figure 7 The long pulse laser 1 emits light for excitation, and the light passing through the first beam splitter 3 reaches the PIN tube 11, which converts the optical signal into an electrical signal to trigger the spectrometer 10. Because the sample is excited to evaporate and cool down to produce plasma after 1μs, and the plasma emits molecular spectrum after 2μs, we set the integration delay of the spectrometer 10 to 3μs and the integration time to 50μs. In this way, the spectrometer 10 starts to open after receiving the electrical signal, and starts to collect when the plasma emits molecular spectrum, and continues until the plasma annihilates, which reduces the background spectrum and signal noise, and enhances the molecular spectrum signal.

[0133] Example 2: High-precision detection of hydrogen / deuterium isotopic abundance and ratio based on molecular emission spectrum

[0134] Traditional laser ablation atomic absorption spectroscopy has significant technical bottlenecks in hydrogen / deuterium isotope analysis. On the one hand, the phenomenon of spectral line Stark broadening is extremely obvious in the laser-induced plume formed under atmospheric pressure; on the other hand, the laser-induced plasma (LIP) of water samples usually has extremely high electron density, thereby significantly exacerbating the degree of spectral line Stark broadening. In particular, the Stark broadening coefficient of the H a and D a emission lines is already at the highest level, resulting in further broadening of the lines and making spectral analysis more difficult. Although delaying the signal acquisition time can inhibit broadening to some extent, the detection signal-to-noise ratio is significantly reduced due to the rapid decay of the emission intensity over time, so traditional laser ablation atomic absorption spectroscopy cannot meet the requirements of high-precision D / H isotope abundance measurement in water. In addition, the isotopic shift in the atomic absorption spectrum of hydrogen is extremely small, with a shift of only about 18 pm between H a and D a , which has approached the resolution limit of most conventional spectrometers 10, making it a challenging task to accurately distinguish between H and D abundance.

[0135] In contrast, molecular spectroscopy exhibits significant advantages in isotope detection. The present embodiment uses a molecular spectroscopy method, which fully utilizes the multiple transition characteristics involving electronic state, vibrational state and rotational state triple energy level structure. The vibrational and rotational energy levels are highly sensitive to the "reduced mass" parameter , and the mass difference between H and D will change significantly, thereby causing significant isotopic spectral shifts. Taking the OH / OD molecule as an example, the isotopic shift in the vibrational-rotational transition can reach several nanometers, which is much larger than the shift of atomic lines, greatly improving the spectral resolution of D / H differences. Furthermore, the rotational lines of the OH / OD molecule are extremely weakly affected by the Stark broadening effect in the plasma environment (the experimentally measured FWHM is only 0.015 nm), the lines are extremely narrow and clear, effectively enhancing the resolution and quantitative accuracy of the molecular spectroscopy signal. In addition, molecular spectra exhibit complex "band structure", consisting of multiple rotational branches, and although the lines are partially overlapped, they provide rich high-dimensional information for multivariate statistical analysis (such as partial least squares regression, PLSR). OH and OD are hydroxyl radicals naturally generated during laser ablation of water samples, and their molecular emission spectra directly reflect the D / H isotope composition in the sample, without any chemical derivatization treatment, enabling in-situ, non-destructive direct detection of the original sample.

[0136] The pulse width of the long pulse laser matches the time scale of molecular bond dissociation and formation, so that the H and D atoms released from the sample can fully react with the O atoms in water to generate OH / OD molecules with high yield. The atomic spectral line density of long pulse laser ablation is low in the near ultraviolet band, and the degree of overlap is small, which is beneficial to the extraction of molecular spectra in the later stage; at the same time, the decay process of the plasma formed is relatively slow, and its temperature can be stably maintained at 7000K, and the electron density can be as high as 101 7 cm - 3, which promotes the generation of excited state molecules and prolongs their emission lifetime. In addition, the plasma induced by long pulse laser has weak shock wave and vertical expansion geometry, which effectively inhibits the entry of external oxygen and improves the reactant transport efficiency; the residual energy of the laser pulse tail further induces secondary evaporation, providing a continuous source of reactants for the generation of OH / OD molecules, thereby forming a cascade amplification effect of molecular emission.

[0137] To enhance the molecular signal intensity and improve the experimental repeatability and detection accuracy, the inert gas argon is selected as the carrier gas in this embodiment. First, the chemical inertness of argon ensures that it does not react with the matrix or the molecules to be detected, and can effectively isolate the active components (such as oxygen, nitrogen, water vapor) in the air, thereby avoiding the induction of non-target reactions (such as oxidation, nitridation or hydration) in the high-temperature environment formed by laser ablation, ensuring the purity and non-interference of OH and OD signals. Second, in the high-temperature plasma, argon excites the emission state of free radicals and molecules in the plasma through Penning ionization and energy transfer processes, enhancing the OH / OD emission intensity. Excited argon atoms (Ar*) are formed under electron collision, which can further transfer energy to OH / OD, making it transition to the radiation state with a higher probability without additional energy loss. In addition, the characteristics of high heat capacity and low thermal conductivity of argon make the plasma cooling rate moderate, reducing the occurrence rate of OH / OD recombination or hydrogen-oxygen exchange, and inhibiting isotopic fractionation; at the same time, the gas flow structure of argon promotes the uniform diffusion of laser ablation particles, improves the spatial uniformity, and improves the signal stability and repeatability.

[0138] During the experiment, the hydroxyl radical (OH) generated by laser ablation in humid argon gas transitions to produce the strongest molecular emission signal, and this spectral band contains 6 main branches (Q 11 , R 11 , P 11 , Q 22 , R 22 , P 22 ) and 6 satellite branches ( 1 Q 12 , 0 P 12 , 0 R 12 , 0 P21 , R Q 21 , s R 21 The Q branch has the highest Hund-London factor and the strongest emission. Therefore, this invention selects the Q branch in the wavelength range of 306–310 nm. 00 Branches were used as targets for molecular spectral acquisition. Experimental results showed that when the argon flow rate was increased to 10 L / min, the signal intensity of the rotational structure in the blank spectrum was significantly reduced, decreasing to <0.1% of the water sample signal, thus significantly suppressing background interference. For OH molecule emission, the acquisition delay time was set to >2 μs to eliminate strong background fluctuations in the early plasma. Observations showed that the net molecular emission intensity increased with time before 8 μs, then rapidly decayed, and the background and noise tended to stabilize after 12 μs. The signal approached the background value at 30 μs, and the SBR and SNR reached their maximum at 8 μs. Therefore, subsequent experiments fixed the acquisition conditions at a delay of 8 μs and a gate width of 50 μs.

[0139] Specifically, plasma is generated by exciting the sample 13 with a single long-pulse laser. The nanoscale isotope shift characteristics of molecular spectra such as OH / OD are utilized, combined with interference suppression in a high-pressure inert gas environment, to achieve in-situ detection of isotope abundance ratios. Specific steps may include:

[0140] A1. Fill a sealed environment with a high-pressure inert gas at a predetermined pressure and place the sample to be tested 13.

[0141] Specifically, the sample to be tested 13 is placed in a sealed sample chamber unit 12, which includes a sealed gas chamber body 121, a gas inlet and outlet 123, a pressure control system, and an optical window 122. Argon gas (high-pressure inert gas) at 101 kPa is introduced into the chamber, and the pressure control system maintains stable gas pressure, suppresses non-target chemical reactions, and stabilizes the plasma temperature. The high heat capacity of the inert gas is used to delay plasma cooling and promote the efficient generation of OH / OD molecules.

[0142] Argon is a chemically inert gas that can isolate air and enhance molecular spectral signals through Penning ionization.

[0143] A2. Emit a long-pulse high-energy laser with an energy greater than a predetermined value, and reflect the long-pulse high-energy laser to focus the high-energy laser onto the surface of the sample 13 to excite the sample 13 to plasma; the long-pulse high-energy laser is a laser pulse with a predetermined duration.

[0144] Start the 1064nm long pulse laser 1 and adjust the output frequency to 1Hz, pulse width to 104ns, and energy to 80mJ (achieved by adjusting the supply current from 1 to 190A and the supply pulse width from 230 to 300μs).

[0145] The laser is transmitted to the first beam splitter 3 through the mirror group 2, and is divided into two beams: one triggers the PIN tube 11 of the spectrometer 10, and the other is transmitted through the dichroic mirror 4 and focused to the sample surface by the microscope objective 5 to form a spot with a diameter of ≤50μm, which excites the generation of plasma.

[0146] A3, after the surface of the sample 13 to be tested is excited by the plasma, the corresponding molecular spectrum signal is acquired and analyzed by molecular spectrum spectrometric detection, so as to realize the detection of the abundance ratio of isotopes.

[0147] When the plasma is cooled to 5000-8000K, the emitted molecular spectrum (such as the 306-310nm waveband of OH / OD) first passes through the fused quartz optical window 122 and then is reflected by the dichroic mirror 4 into the spectrometer 10.

[0148] The Model 209 monochromator (1200 lines / mm grating, resolution 0.015nm) and the ICCD 105 detector are used to set the delay to 8μs and the gate width to 50μs, and the spectral signal is collected under the triggering of the PIN tube 11.

[0149] The collected data are sequentially subjected to asymmetric least squares (AsLS) baseline correction, statistical sensitive nonlinear iterative peak (SNIP) background removal, loading of HITRAN database molecular constants (such as rotational / vibrational constants) for Voigt line fitting, and calculation of the isotopic abundance ratio by partial least squares regression (PLSR). The data analysis here is actually two kinds: one is molecular spectrum fitting, which involves the processes of AsLS baseline correction and SNIP background removal, loading of HITRAN database molecular constants (such as rotational / vibrational constants) for Voigt line fitting. The second is to measure the molecular emission spectrum of different standard samples, to pre-process the spectral data (background removal, smoothing), to use the pre-processed spectral data to establish a PLSR model, to use cross-validation (such as leave-one-out or k-fold) to determine the optimal principal component number, and to use the optimized model established by the model to predict the abundance ratio of unknown samples.

[0150] Objective: In the spectrum y i Fit a smooth baseline z i Make the residuals more sensitive to negative deviations. Optimize the objective:

[0151]

[0152] Where the weights

[0153]

[0154] · λ: smoothing parameter, the greater the baseline is smoother (typical value 102 ~10 9 ).

[0155] • p: Asymmetric penalty parameter, range (0, 1), typically p ~ 10 -2 to 10 -1 .

[0156] • Number of iterations: typically 10-20, until weights converge.

[0157] AsLS baseline correction

[0158] Goal: iteratively "sharpen" background, preserving narrow peaks, by local minimum iteration. Core of the algorithm (pseudo-code):

[0159] 1. Set original spectrum y 2. For iteration step k = 1 to K:

[0160]

[0161] where window half-width m varies with k, and can be set as

[0162] 3. Final background estimate Subtract to get signal s i = y i - b i .

[0163] • K: Total number of iterations, commonly 20-100.

[0164] • Window growth strategy: can be linear or square root, affecting the degree of background smoothing.

[0165] SNIP background removal

[0166] Voigt function is the convolution of Gaussian and Lorentzian, used to describe both Doppler broadening and optical broadening.

[0167]

[0168] where

[0169]

[0170] A: Peak intensity (area or peak height)

[0171] x0: Peak center position.

[0172] σ: Gaussian width parameter (related to half-height width ).

[0173] - γ: Lorentzian width parameter (half-width, H L = 2γ).

[0174] {A, x0, s, g} are optimized simultaneously during fitting, commonly using the non-linear least squares (Levenberg-Marquardt) algorithm.

[0175] Voigt profile fitting model expression: X ∈ R n×p (spectrum matrix) and Y ∈ R n×q (concentration / abundance matrix) are decomposed as:

[0176]

[0177]

[0178] W: weight matrix, each column is the weight vector of the h-th component.

[0179] P, Q: load matrix, corresponding to X and Y respectively.

[0180] T, M: score matrix.

[0181] H: number of principal components (latent variables).

[0182] Cross-validation indicators: RMSECV, R 2 Used to select the optimal H.

[0183] PLSR

[0184] A4, auto-focusing and sample positioning

[0185] Turn on the LED illumination focusing unit, its built-in white light source is reflected by the reflector 7, and then focused on the surface of the sample 13 to be measured through the microscope objective 5, forming an illumination spot. The computer 15 drives the three-dimensional displacement table 9 to move the sample table 94 in the X / Y plane to select the detection area, and synchronously adjusts the Z-axis height.

[0186] Real-time image acquisition of the surface of the sample 13 to be measured by the camera 8, when the image texture clarity reaches the threshold value (such as the peak value of the gray gradient), it is determined that the focusing is completed, and the accuracy is ±5μm; the system automatically records the three-dimensional coordinates of the current detection point, which is used for path planning of subsequent multi-point detection.

[0187] A5, system calibration

[0188] The heavy water standard sample with known D / H ratio (such as D / H = 0.0156) is placed in a sealed sample chamber as a calibration sample; the energy of the long pulse laser 1 is adjusted to 80 mJ, the output frequency is 1 Hz, and the laser energy is calibrated by a power meter; the center wavelength of the spectrometer 10 is set to 310 nm (OH molecular characteristic peak band), the delay of the ICCD 105 detector is 8 μs, the gate width is 50 μs, and the standard sample spectrum is collected.

[0189] An energy scanning experiment is performed, the power supply current (1-190 A) is adjusted to make the signal-to-noise ratio of the OH / OD spectrum line ≥200:1, and the light path transmission efficiency is simultaneously optimized; a partial least squares regression (PLSR) model is established based on the standard sample spectrum, the detection limit is verified to be ≤0.1%, the repeatability error is <2%, and the industrial detection accuracy is ensured. The results are shown in Figure 9 and Figure 10 .

[0190] Example 3: High-precision detection of CC isotope abundance and ratio based on molecular emission spectrum

[0191] 1. First, the CC isotope-enriched benzoic acid sample to be tested is placed in a sealed sample chamber, and the sealed chamber is closed. The inert gas is argon. Compared with air or nitrogen, the plasma generated by laser ablation in argon has a longer high-temperature retention time. This is because argon, as an inert gas, has low thermal conductivity, which can effectively slow down the energy dissipation. At the same time, nitrogen is prone to molecular dissociation at high temperatures, consuming a large amount of energy in the process and further dissipating energy through its complex intramolecular freedom channel. In addition, nitrogen atoms have certain chemical activity in the excited state, which also leads to further energy loss. Argon does not participate in chemical reactions, which is conducive to maintaining a higher energy state in the plasma. In this environment, the formation of C2 does not depend on the reaction with atmospheric components, making argon a more ideal background gas that can provide sufficient energy in the gas phase of the ablation plume to fully dissociate the material and obtain a longer time to reach thermodynamic equilibrium. Overall, an argon atmosphere is more conducive to complete atomization of the ablation plume, thereby improving the analysis accuracy and plasma stability. The gas inlet of the sealed sample chamber is connected to the argon cylinder, the argon cylinder valve is opened, and the gas chamber pressure gauge is observed. When the argon pressure in the sealed sample chamber is 101 kPa, the gas inlet of the sealed sample chamber is automatically closed to ensure that the argon inside the chamber is always at 101 kPa.

[0192] 2. Rotate the mirror on the corner of the spectrometer 10 to the right, select the ICCD 105 camera 8, open the ICCD 105 software using the computer 15, then wait for the temperature to drop to -20°C, connect the 209 spectrometer 10, select the wavelength as the abscissa, the grating line number is selected as 1200, set the center wavelength of the detection as 475 nm, and the center wavelength to be observed should be the same as the current dial reading. The trigger mode of the ICCD 105 is selected as external trigger, the exposure time of the ICCD 105 is 100 μs. The delay of the ICCD 105 is 5.5 μs, the gate width is 70 μs, the gain is 4000, and the path and format of data saving are set.

[0193] 3. Place the sealed sample chamber on the sample table 94, use the computer 15 to control the three-dimensional displacement table 9 to move in the X and Y planes, select an appropriate sample point, then turn on the LED illumination light source, insert the mirror 7, and observe the sample surface through the camera 8. Move the Z axis of the displacement table until the clearest image of the sample surface appears in the camera 8, indicating that the focusing has been completed. Then turn off the LED light source and remove the mirror 7.

[0194] 4. Turn on the long pulse laser 1, adjust the frequency of the long pulse laser 1 to 10 Hz, and the pulse width to 104 ns. Place the power meter probe at the long pulse laser port position, adjust the laser power supply current to adjust the energy of the long pulse laser, until the energy of the long pulse laser is 100 mJ. Turn off the lights in the laboratory, turn on the ICCD 105 of the spectrometer 10, then adjust the frequency of the laser to 1 Hz, and start emitting the long pulse laser.

[0195] 5. The long pulse laser first passes through the mirror group 2 to the first beam splitter 3. At this time, the laser will be divided into two beams. One beam transmits through the first beam splitter 3 and is incident on the PIN tube 11, which outputs an electrical signal to the spectrometer 10, so that the triggering and detection can be realized to work together, without triggering the spectrometer 10 to start collecting the spectrum. The other beam is reflected by the first beam splitter 3 to the dichroic mirror 4. The long pulse laser transmits through the dichroic mirror 4 to the microscope objective 5, which focuses the long pulse laser onto the surface of the sample to be measured 13, thereby increasing the instantaneous peak power density of the long pulse laser to break down the sample to be measured 13.

[0196] 6. When the sample to be measured 13 is broken down, it will be instantaneously gasified to form high-energy plasma. During the cooling process of the plasma, it will first continuously radiate full-spectrum signals, then emit atomic spectrum after 1 μs, and then combine atoms to form molecules after 2 μs, thereby radiating molecular spectrum outward. Because the masses of molecular isotopomers are different, the molecular emission band head will be displaced. The band head displacement is about 0.1 nm, and the resolution of the spectrometer 10 is 0.015 nm.

[0197] 7、Plasma emitted molecular spectrum will be reflected by the dichroic mirror 4 to the coupling mirror, the signal spectrum will be coupled into the optical fiber, then the signal light in the optical fiber will be incident to the collimating mirror 108 inside the spectrometer 10 through the slit 109, the collimated parallel light will reach the grating of the ruled line 1200, the grating will separate the composite light into the monochromatic light with the center wavelength of 475nm, the monochromatic light will be focused to the surface of the ICCD 105 through the focusing lens 103.

[0198] 8、The ICCD 105 is in working state under the triggering of the PIN tube 11, the molecular light signal after the light splitting will be detected, and the collected signal light condition can be observed in the camera 8.

[0199] 9、The collected molecular spectrum data is exported for data processing, first, the baseline correction and background removal of the data are performed, the asymmetric least squares AsLS and SNIP are adopted to select and remove the slowly changing background.

[0200] 10、Then, the polynomial fitting and automatic background correction are performed, the continuous wavelet transform combined with interpolation can efficiently remove the residual baseline.

[0201] 11、The processed data is imported into the Pgopher software, the wavelength is selected as the horizontal coordinate unit, and the data is ensured to be displayed in two-dimensional graphics to display the total information of the data

[0202] 12、The molecular constants including the rotational constant and the vibrational constant are loaded, and the line list containing the spectral line data of the molecule is loaded.

[0203] 13、The fitting setting window is opened, the rotational constant and the vibrational constant parameters to be fitted are selected, and the initial guess value and the fitting range are set.

[0204] 14、The automatic molecular spectrum fitting is adopted, the fitting result is observed, and the residual and the intensity residual are checked.

[0205] 15、The energy level state information and the spectral transition information are viewed, and the isotopic abundance and ratio are calculated by the software. The result is shown as Figure 11 .

[0206] Example 4: High-precision detection of OH isotopic abundance and ratio based on molecular emission spectrum

[0207] 1、Use ordinary water ice as 16 the reference sample of OH molecular isotopes, heavy water ice is used for studying 16 OD molecular isotopic spectrum, 18 O-enriched ice is used for measuring 18 OH molecular isotopes.

[0208] 2、Seal the sample cabin 14 and fill it with argon.

[0209] 3. The central wavelength of the spectrometer 10 is set to 310 nm, the delay of the ICCD 105 is 8 μs, and the gate width is 50 μs.

[0210] 4. The energy of the long pulse laser 1 is set to 80 mJ.

[0211] Other operations are the same as in Example 3. The results are shown in Table 12. Among them, Figure 13 is a control in an air atmosphere, and Figure 12 and Figure 13 According to the results of the above, the present application prolongs the plasma lifetime to 50-100 μs by filling 101 kPa of argon or helium, increases the molecular emission intensity by 3 times, and reaches a signal-to-noise ratio of 200:1, which is much higher than 80:1 of other commonly used measurement systems. The 104 ns pulse width of the long pulse laser 1 provides sufficient energy to ablate the sample, while avoiding the plasma transient instability caused by the femtosecond laser. The delay of 2-5 μs for collecting the molecular spectrum effectively avoids the interference of atomic lines, and in combination with the spectrometer 10, the isotopic abundance detection limit is as low as 0.1%, which is better than 0.5-1% of the existing commonly used measurement systems. The repeatability error of the present application is less than 2%, which meets the industrial high-precision requirements.

[0212] Example 5: High-precision detection of CN isotopic abundance and ratio based on molecular emission spectrum

[0213] 1. The N-isotope enriched benzamide particle sample is used as 14 N, 15 N reference sample, and the decanoic acid powder is used as 12 C, 13 C reference sample.

[0214] 2. The inert gas for sealing the sample chamber 14 is helium, which is light and chemically inert, suitable for quickly removing the ambient gas, reducing the collision interference between molecules, and has high thermal conductivity of helium, which can accelerate the cooling of the plasma and promote the recombination of molecules.

[0215] 3. The central wavelength of the spectrometer 10 is set to 420 nm, the delay of the ICCD 105 is 40 μs, and the gate width is 100 μs.

[0216] 4. The energy of the long pulse laser 1 is set to 32 mJ.

[0217] Other operations are the same as in Example 3. The results are shown in Table 12. Among them, Figure 14 .

[0218] The above-described embodiments of the present application do not constitute a limitation on the protection scope of the present application. Any modification, equivalent replacement, and improvement made within the spirit and principles of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A device for detecting isotopic abundance and ratio based on molecular emission spectroscopy, characterized in that, include: A single long-pulse laser (1) is used to emit laser pulses with a pulse width ≥100ns, a frequency of 1~10HZ, and an energy of 0~120mJ to excite the sample to be tested (13) to generate plasma; The optical path transmission unit is used to receive long pulse laser and reflect and focus the laser onto the surface of the sample to be tested (13) through the reflector group (2), the first beam splitter (3), the dichroic mirror (4) and the microscope objective (5), while introducing the plasma emission light into the detection optical path. The LED illumination focusing unit includes LED white light illumination (6), a reflector (7) and a monitoring camera (8) for providing auxiliary white light illumination under the microscope objective (5) and observing the focal plane in real time; A three-dimensional displacement stage (9) is connected to a computer (15) for locating detection points in the X / Y plane and achieving automatic or manual focusing in the Z direction; The sealed sample chamber unit (12) includes a sealed gas chamber body (121), an optical window (122), a gas inlet and outlet (123) and a pressure control system, which are used to maintain an inert gas environment of 101 kPa ± 1 kPa in the area of ​​the sample to be tested (13); The spectrometer (10) includes a collimating lens (108), a focusing lens (103), a planar grating (101), a grating driver (102), and an ICCD (105), and supports adjustable parameters such as external triggering, delay, gate width, and gain for molecular spectroscopy and detection. Computer (15) is connected to long pulse laser (1), optical path transmission unit, LED illumination focusing unit, three-dimensional displacement stage (9), and spectrometer (10) to control the emission timing and parameters of long pulse laser (1); drive LED illumination focusing unit and three-dimensional displacement stage (9) to achieve focusing and sample point switching; adjust the center wavelength of spectrometer (10) and ICCD (105) gate parameters and trigger spectral acquisition; perform baseline correction, background removal and multi-peak fitting on the acquired molecular spectrum, and calculate the isotope abundance and ratio of the sample (13) to be tested; the spectrometer (10) includes a PIN tube trigger circuit, the PIN tube receives the laser pulse transmitted by the first beam splitter (3) and outputs a trigger signal to realize ICCD (105) external trigger acquisition, the delay is set to 2-50μs, and the gate width is set to 20-150μs.

2. The isotope abundance and ratio detection device based on molecular emission spectroscopy according to claim 1, characterized in that, The long-pulse laser (1) includes: Pump cavity, used to provide pump energy for the laser medium and achieve population inversion; An acousto-optic Q-switching cavity includes a transducer, power supply, acousto-optic medium, sound-absorbing material, and cooling system. It achieves instantaneous laser release through Q-switching via acousto-optic diffraction. The laser controller and its supporting software are used to adjust the pump source drive, Q switch trigger and laser output parameters, and communicate with the computer (15).

3. The isotope abundance and ratio detection device based on molecular emission spectroscopy according to claim 1, characterized in that: The mirror group (2) includes 6 mirrors. The long pulse laser (1) emits laser light, which passes through the lifting optical path composed of two mirrors to reach the two mirrors constrained by the cage structure. The cage structure remains horizontal. Then, it passes through the lifting optical path composed of two mirrors and enters the first beam splitter (3). One beam of light shines on the PIN tube, and the other beam of light passes through the dichroic mirror (4) and is focused onto the surface of the sample to be tested (13) through the microscope objective (5).

4. The isotope abundance and ratio detection device based on molecular emission spectroscopy according to claim 3, characterized in that: The first beam splitter (3) is placed behind the last reflector. The first beam splitter (3) uses the reflection and transmission characteristics of the optical thin film to split the incident light into two parts. When the beam passes through the first beam splitter (3), part of the light is reflected and the other part of the light passes through the first beam splitter (3). The transmitted light shines on the PIN tube and the reflected light is incident on the dichroic mirror (4). The dichroic mirror (4) is positioned below the first beam splitter (3), and the dichroic mirror (4) separates the excitation laser from the plasma emission light; The reflector (7) is detachably installed below the dichroic mirror (4). The reflector (7) is used to reflect the light source emitted by the LED light source to achieve imaging and focusing. In the absence of focus, the operator removes the reflector (7), and the laser light passing through the dichroic mirror (4) directly reaches the microscope objective (5). The long pulse laser light reaching the microscope objective (5) will be focused to excite the sample (13) to generate plasma. After the reflector (7) is installed, it is combined with the LED illumination focusing unit to generate imaging effect. The molecular signal light generated by the plasma is collected and coupled into the optical fiber for spectroscopic detection.

5. The isotope abundance and ratio detection device based on molecular emission spectroscopy according to claim 1, characterized in that: The pressure control system of the sealed sample chamber unit (12) includes a pressure sensor, a regulating valve and a safety alarm device, which are used to monitor and maintain the inert gas pressure within a preset range of 101 kPa ± 1 kPa in real time.

6. The isotope abundance and ratio detection device based on molecular emission spectroscopy according to claim 1, characterized in that: The computer (15) calls the molecular spectroscopy fitting software, loads the rotation-vibration constant and spectral line list, automatically completes the multi-peak fitting and outputs the isotope abundance and ratio.

7. A method for detecting isotopic abundance and ratio based on molecular emission spectroscopy, characterized in that, The isotope abundance and ratio detection device based on molecular emission spectroscopy as described in any one of claims 1-6 includes the following steps: (1) Placement of the sample to be tested (13): Place the isotopically enriched sample (13) particles into the sealed sample chamber unit (12) and adjust the inert pressure to 101kPa±1kPa. (2) Microscopic focusing: Turn on LED white light illumination (6) and drive the three-dimensional displacement stage (9) to make the surface of the sample (13) coincide with the focal plane of the microscope objective (5); (3) Plasma excitation: The long pulse laser (1) is triggered according to the set working frequency and energy, and focused onto the surface of the sample (13) to be tested through the optical path transmission unit to generate plasma; (4) Spectral acquisition: Rotate the grating to adjust the center wavelength of the spectrometer (10). The plasma emits molecular spectra 2-15μs after excitation. The signal is reflected by the dichroic mirror (4) and coupled into the optical fiber. Under the trigger of the PIN tube, the ICCD (105) acquires the signal at a gate width of 30-150μs. (5) Data processing: Apply AsLS and SNIP algorithms to the original spectra for baseline correction and background removal, and then analyze the molecular spectra of isotopes through multi-peak fitting. (6) Isotope calculation: Call the molecular spectroscopy fitting software, load the list of molecular constants and spectral lines, automatically fit and output the isotope abundance and ratio of the sample to be tested (13).

8. The isotope abundance and ratio detection method according to claim 7, characterized in that, The AsLS and SNIP algorithms are used individually or in combination, and residual baselines are removed by continuous wavelet transform and interpolation.

9. The isotope abundance and ratio detection method according to claim 7, characterized in that, The spectrometer (10) has a center wavelength in the range of 190~800nm, which is driven by a stepper motor and a sine arm to scan the grating. The wavelength repeatability is ±0.005nm.

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