A polarization LIBS-LIF system for trace element detection

Abstract

This application belongs to the field of spectroscopic detection technology and relates to a polarized LIBS-LIF system for trace element detection. The system includes: a laser emitting unit, a first optical path structure, an optical parametric oscillator, a second optical path structure, a displacement platform, a polarization acquisition module, and an analysis and control module. The laser emitting unit emits a first laser beam into the first optical path structure. The first optical path structure converts the received first laser beam into circularly polarized light and directs it into the sample on the displacement platform. The optical parametric oscillator emits a second laser beam into the second optical path structure. The second optical path structure focuses the second laser beam and directs the circularly polarized light to the same position on the sample to excite the analyte in the plasma. The polarization acquisition module acquires the plasma spectral signal, converts it into an electrical signal, and transmits it to the analysis and control module. This application can improve plasma excitation efficiency, reduce the detection limit, and improve the stability of detection results.

Description

Technical Field

[0001] This application belongs to the field of spectroscopic detection technology, and more specifically, relates to a polarization LIBS-LIF system for trace element detection. Background Technology

[0002] Laser-induced breakdown spectroscopy (LIBS) uses an ultrashort pulse laser to focus on the sample surface, ablating it to generate high-temperature plasma. The emission spectrum of this plasma is then analyzed to determine the elemental composition and content of the sample. Laser-induced fluorescence-assisted laser-induced breakdown spectroscopy (LIBS-LIF) builds upon LIBS by using a second laser (resonance laser) to further excite specific elements in the plasma. Lower-level atoms absorb energy and are excited to higher energy levels, transitioning downwards to produce fluorescence, thus enhancing the spectrum. LIBS-LIF technology has broad application prospects in environmental monitoring, biomedicine, and food testing.

[0003] Despite the advantages of LIBS-LIF technology, such as eliminating spectral interference, rapid detection, and high sensitivity, it still faces some challenges in practical applications. These include poor spectral signal stability and insufficient sensitivity for detecting trace elements in complex matrices. Traditional LIBS-LIF systems use linearly polarized laser light for excitation, affecting the excitation efficiency and characteristics of the plasma. Laser-induced plasma is a highly complex transient process, susceptible to significant fluctuations due to external factors, including uneven plasma particle number density distribution, temperature, and morphological changes. This results in poor spectral stability, posing a challenge to the accurate quantification of trace elements in samples by LIBS-LIF. Furthermore, conventional linearly polarized light, due to its fixed electric field direction, cannot continuously accelerate electrons when interacting with matter. The lower electron kinetic energy leads to insufficient plasma density and a relatively small number of ground-state particles, limiting the number of particles excited by the resonant laser and thus restricting further enhancement of spectral intensity, making the detection of low-concentration trace elements even more difficult. In addition, for some heavy metals that the human body cannot metabolize, such as lead, even extremely low doses of exposure can accumulate in the body, causing irreversible health damage. Therefore, a device for detecting trace elements is needed to solve the above problems. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this application is to provide a polarization LIBS-LIF system for trace element detection. This system aims to solve the problems of existing LIBS-LIF systems being susceptible to large fluctuations due to external factors during laser-induced plasma detection, and the poor spectral stability caused by uneven plasma particle number density distribution, temperature changes, and morphological changes, which affect the accurate quantitative detection of trace elements.

[0005] To achieve the above objectives, this application provides a polarized LIBS-LI F system for trace element detection. The system includes: a laser emitting unit, a first optical path structure, an optical parametric oscillator, a second optical path structure, a displacement platform, a polarization acquisition module, and an analysis and control module. The laser emitting unit emits a first laser beam into the first optical path structure. The first optical path structure converts the received first laser beam from linearly polarized light to circularly polarized light and directs the circularly polarized light onto a sample on the displacement platform to excite plasma. The optical parametric oscillator emits a second laser beam into the second optical path structure. The second optical path structure focuses the second laser beam and directs it to the same position on the sample where the circularly polarized light was incident, thereby exciting the analyte in the plasma. The polarization acquisition module acquires the plasma spectral signal of the excited analyte and converts the plasma spectral signal into an electrical signal, which is then transmitted to the analysis and control module for analysis.

[0006] Compared with the prior art, the LIBS-LIF detection system provided in this application can achieve polarization excitation and polarization resolution in trace element detection, thereby improving excitation efficiency and detection result stability by changing the polarization state of the excitation laser.

[0007] Furthermore, the first optical path structure includes a laser wavelength reflector, a polarizing optical element, and a first laser focusing lens, wherein: the laser wavelength reflector forms an acute angle with the first laser beam, which is used to reflect the first laser beam and then perpendicularly enter the polarizing optical element; the polarizing optical element and the first laser focusing lens are coaxial and parallel, which is used to convert the received first laser beam into circularly polarized light and then perpendicularly enter the sample.

[0008] Furthermore, the second optical path structure includes a second laser focusing lens, which is perpendicular to the propagation direction of the second laser beam, and is used to focus the second laser beam and direct it into the same position as the circularly polarized light that strikes the sample.

[0009] Furthermore, the polarization acquisition module includes a third optical path structure, a spectrometer, and an ICCD. The third optical path structure includes a first focusing lens, a polarizer, and a second focusing lens arranged coaxially and parallel to each other. The first focusing lens is used to focus the plasma spectral signal and transmit it to the polarizer. The polarizer is used to suppress background noise in the plasma spectral signal and then transmit the plasma spectral signal to the second focusing lens. The second focusing lens is used to focus the plasma spectral signal and then transmit it sequentially to the spectrometer and ICCD via optical fiber.

[0010] Furthermore, the analysis and control module includes a timing controller, which is connected to the laser emitting unit and the optical parametric oscillator respectively, and is used to control the laser pulse emission delay between the first laser beam and the second laser beam; the timing controller is also connected to the ICCD and is used to control the acquisition delay of the ICCD.

[0011] Furthermore, the analysis and control module also includes a computer, which is connected to both the optical parametric oscillator and the ICCD. The computer is used to control the output wavelength of the optical parametric oscillator and to analyze the plasma spectral signals acquired by the ICCD and display the spectral images.

[0012] Furthermore, the laser pulse emission delay between the first laser beam and the second laser beam is at least 10 μs.

[0013] Furthermore, the wavelength range of the optical parametric oscillator is 251.51nm-251.71nm.

[0014] Furthermore, the wavelength of the optical parametric oscillator is 251.61 nm.

[0015] Furthermore, the polarizer can be rotated to a specific angle to remove the spectral background of the element to be measured.

[0016] In summary, compared with the prior art, the technical solutions conceived in this application have the following main technical advantages:

[0017] 1. The polarization LIBS-LIF system for trace element detection provided in this application improves plasma excitation efficiency and enhances the stability of detection results by changing the laser polarization state; it uses a polarization acquisition module to suppress background signals in the plasma excitation spectrum signal, further improving the signal-to-background ratio of the detection signal, achieving high-sensitivity detection of trace element characteristic spectral lines, and further improving the accuracy of the LIBS-LIF system in quantitative analysis.

[0018] 2. The polarization LIBS-LIF system for trace element detection provided in this application achieves the effect of changing the polarization state of the laser using only one mirror, one polarization optical element and two focusing mirrors in its first optical path structure. No other complex optical path system is required. The overall polarization LIBS-LIF system has a simple and compact structure, which is easy to adjust and maintain. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the polarization LIBS-LIF system provided in the embodiments of this application;

[0020] Figure 2 This is a comparison of the characteristic spectral peaks of silicon (SiI) at 288.16 nm in microalloyed steel detected by the conventional detection system provided in this application under linear polarization and by the polarization LIBS-LIF system of this application under circular polarization.

[0021] Figure 3 This is a comparison chart of the fluctuation performance of the conventional detection system provided in this application under linear polarization and the polarization LIBS-LIF system of this application under circular polarization, measured one hundred times respectively.

[0022] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0023] 1-Laser emitting unit, 2-Optical parametric oscillator, 3-Optical path structure, 4-Displacement platform, 5-Polarization acquisition module, 6-Spectrometer, 7-ICCD, 8-Timing controller, 9-Computer, 10-Laser wavelength reflector, 11-Polarization optical element, 12-First laser focusing lens, 13-Second laser focusing lens, 14-First focusing lens, 15-Polarizer, 16-Second focusing lens, 17-Fiber optic cable. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0025] This application provides a polarization LIBS-LIF system for trace element detection. The system includes a laser emitting unit 1, a first optical path structure, an optical parametric oscillator 2, a second optical path structure, a displacement platform 4, a polarization acquisition module 5, and an analysis and control module. The laser emitting unit 1 emits a first laser beam into the first optical path structure. The first optical path structure converts the received first laser beam from linearly polarized light to circularly polarized light, and directs the circularly polarized light into the sample on the displacement platform 4 to excite plasma. The optical parametric oscillator 2 emits a second laser beam into the second optical path structure. The second optical path structure focuses the second laser beam and directs the circularly polarized light to the same position on the sample to excite the analyte in the plasma. The polarization acquisition module acquires the plasma spectral signal of the excited analyte and converts the plasma spectral signal into an electrical signal, which is then transmitted to the analysis and control module.

[0026] Specifically, the aforementioned laser emitting unit 1 is an Nd:YAG laser, used to generate high-energy, stable, and repeatable laser pulses to ablate the sample and generate plasma on the sample surface. The displacement platform 4 is used to place the sample to be analyzed and can move the sample at a uniform speed in any direction. The polarization acquisition module 5 is used to acquire the spectrum and convert the optical signal into an electrical signal. The analysis and control module is used to control the coordinated operation of the laser and the polarization acquisition module, process and analyze the electrical signal, plot the corresponding spectrum, and display the results.

[0027] More specifically, the first laser beam generated by the Nd:YAG laser is converted from linearly polarized light to circularly polarized light after passing through the first optical path structure; the second laser beam generated by the optical parametric oscillator 2 is injected into the same point on the sample surface as the circularly polarized light after passing through the second optical path structure, and the transmission directions of the two laser beams are perpendicular to each other.

[0028] The aforementioned first optical path structure includes a laser wavelength reflector 10, a polarizing optical element 11, and a first laser focusing lens 12, wherein: the laser wavelength reflector 10 forms an acute angle with the first laser beam, which is used to reflect the first laser beam and then perpendicularly enter the polarizing optical element 11; the polarizing optical element 11 and the first laser focusing lens 12 are coaxial and parallel, which is used to convert the received first laser beam into circularly polarized light and then perpendicularly enter the sample.

[0029] Specifically, the laser wavelength reflector 10 has an angle of 45 degrees with the first laser beam and also has an angle of 45 degrees with the polarization optical element 11. The polarization optical element 11 is a quarter-wave plate with a working wavelength of 532nm. The fast axis of the quarter-wave plate is rotated on the horizontal plane to an angle of 45 degrees with the polarization direction of the first laser beam. When the linearly polarized light reflected by the laser wavelength reflector 10 passes through the quarter-wave plate, the polarization component undergoes a phase delay, and the linear polarization state can be converted into a circular polarization state.

[0030] The aforementioned second optical path structure includes a second laser focusing lens 13, which is perpendicular to the propagation direction of the second laser beam and is used to focus the second laser beam and direct it into the same position as the circularly polarized light that strikes the sample.

[0031] The aforementioned polarization acquisition module includes a third optical path structure, a spectrometer 6, and an ICCD 7. The third optical path structure includes a first focusing lens 14, a polarizer 15, and a second focusing lens 16 arranged coaxially and parallel to each other. The first focusing lens 14 is used to focus the plasma spectral signal and transmit it to the polarizer 15. The polarizer 15 is used to suppress background noise in the plasma spectral signal and then transmit the plasma spectral signal to the second focusing lens 16. The second focusing lens 16 focuses the plasma spectral signal and then transmits it sequentially to the spectrometer 16 and the ICCD 7 via the optical fiber 17.

[0032] The aforementioned analysis and control module includes a timing controller 8, which is connected to both the laser emitting unit 1 and the optical parametric oscillator 2, and is used to control the laser pulse emission delay between the first laser beam and the second laser beam. The timing controller 8 is also connected to the ICCD7, and is used to control the acquisition delay of the ICCD7. The analysis and control module also includes a computer 9, which is connected to both the optical parametric oscillator 2 and the ICCD7, and is used to control the output wavelength of the optical parametric oscillator 2, as well as to analyze the plasma spectral signals acquired by the ICCD7 and display the spectral images.

[0033] When using the polarized LIBS-LIF system for trace element detection provided in this embodiment for actual detection, the Nd:YAG laser 1 is first controlled to generate a first laser beam. The first laser beam is focused onto the surface of the sample to be tested by the laser wavelength reflector 10, the polarization optical element 11, and the first laser focusing lens 12 in sequence, thereby exciting and generating plasma. After a certain delay time, the optical parametric oscillator 2 is controlled to generate a second laser beam. The second laser beam is focused onto the same position on the surface of the sample to be tested by the first laser beam through the second laser focusing lens 13, thereby selectively exciting the atoms of the element to be tested in the plasma. After excitation, the plasma spectrum is incident parallel to the polarizer 15 through the first focusing lens 14. By rotating the polarizer 15, the angle with the best effect of removing the background of the target element spectrum is selected. After reducing the background signal interference, the plasma spectrum enters the second focusing lens 16 for focusing and is transmitted through the optical fiber 17 to the spectrometer 6 and ICCD 7 for spectral acquisition and electrical signal conversion in sequence. The electrical signal is then transmitted to the computer 9 for processing and analysis. The computer 9 performs qualitative analysis on the sample based on the measured spectral wavelength and quantitative analysis based on the emitted light intensity to determine the content of trace elements.

[0034] To demonstrate the optimal detection results achievable by the polarized LIBS-LIF system for trace element detection provided in the above embodiments, silicon in microalloyed steel was detected and analyzed in detail using both a conventional detection system and the polarized LIBS-LIF system provided in this embodiment.

[0035] When using the polarization LIBS-LIF system provided in this embodiment for detection and analysis, the operating parameters of the Nd:YAG laser, optical parametric oscillator 2, ICCD 7, and timing controller 8 need to be adjusted first to obtain the best spectral results. The specific operating parameters are as follows: the wavelength of the Nd:YAG laser is 532 nm, the laser single-pulse energy is 50 mJ, and the frequency is 10 Hz; the wavelength of the optical parametric oscillator 2 is 251.61 nm, the laser single-pulse energy is 1 mJ, and the frequency is 10 Hz; the time interval between two laser pulses is set to 10 μs for the timing controller 8; the acquisition gate width of the ICCD 7 is 10 ns, the delay is 10 μs, and 100 spectra are acquired.

[0036] Then the required plasma spectrum was detected and acquired, such as... Figure 2 The figure shows a comparison of the spectral intensities of a traditional detection system using a linearly polarized laser beam for excitation detection and the system provided in this application using a circularly polarized laser beam for excitation detection. This illustrates that circularly polarized excitation has the effects of spectral enhancement, lower detection limit, and improved detection sensitivity. The horizontal axis represents the wavelength of the spectrum, and the vertical axis represents the intensity.

[0037] Figure 3 This is a comparison graph showing the fluctuation of the traditional detection system under linear polarization and the polarization LIBS-LIF system of this application under circular polarization, measured one hundred times respectively. The horizontal axis represents the number of measurements, and the vertical axis represents the spectral intensity of each measurement. This shows that the spectrum obtained under circular polarization has smaller fluctuations and is more stable.

[0038] The test results are shown in Table 1. Compared with the traditional test system that uses a linearly polarized laser beam for excitation and detection, the intensity of the characteristic spectral line of Si with a wavelength of 288.16 nm obtained by using a circularly polarized laser beam for excitation and detection provided in this application is increased by 1.2 times, the relative standard deviation (RSD) is reduced by 6.28%, and the signal-to-noise ratio (SNR) is increased by 1.14 times.

[0039] Table 1

[0040]

[0041] Compared with the prior art, the LIBS-LIF detection system provided in this application can achieve polarization excitation and polarization resolution in trace element detection, thereby improving excitation efficiency and detection result stability by changing the polarization state of the excitation laser.

[0042] It should be understood that expressions such as "comprising" and "may include" as used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "comprising" and / or "having" may be interpreted as indicating a specific characteristic, number, operation, constituent element, component, or combination thereof, but should not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0043] It should be understood that the terms “center,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “inner,” “outer,” “clockwise,” “counterclockwise,” “axial,” “radial,” and “circumferential” indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0045] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0046] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A polarized LIBS-LIF system for trace element detection, characterized in that, The system comprises a laser emitting unit (1), a first optical path structure, an optical parametric oscillator (2), a second optical path structure, a displacement platform (4), a polarization acquisition module (5) and an analysis control module; the first optical path structure comprises a laser wavelength reflecting mirror (10), a polarized optical element (11) and a first laser focusing lens (12); the laser wavelength reflecting mirror (10) is at an acute angle with the first laser beam emitted by the laser emitting unit (1), so that the first laser beam is reflected and vertically enters the polarized optical element (11); the polarized optical element (11) and the first laser focusing lens (12) are coaxial and parallel, for focusing the first laser beam after converting it into circularly polarized light and vertically entering the sample to excite the plasma; the second optical path structure comprises a second laser focusing lens (13) which is perpendicular to the propagation direction of the second laser beam emitted by the optical parametric oscillator (2), for focusing the second laser beam and obliquely entering the same position as the circularly polarized light to excite the element to be measured in the plasma; the polarization acquisition module (5) comprises a third optical path structure, a spectrometer (6) and an ICCD (7), the third optical path structure comprises coaxial and parallel first focusing lens (14), polarizer (15) and second focusing lens (16), the first focusing lens (14) is used for focusing and transmitting the plasma spectrum signal to the polarizer (15), the polarizer (15) is used for suppressing the background noise in the plasma spectrum signal, and the plasma spectrum signal is transmitted to the second focusing lens (16) for focusing, and then transmitted to the spectrometer (6) and the ICCD (7) in sequence through the optical fiber (17) for photoelectric conversion, and the obtained electrical signal is transmitted to the analysis control module for analysis.

2. A polarized LIBS-LIF system for trace element detection as claimed in claim 1, wherein, The analysis control module comprises a time sequence controller (8) connected with the laser emitting unit (1) and the optical parametric oscillator (2) respectively, for controlling the laser pulse emission delay between the first laser beam and the second laser beam; the time sequence controller (8) is also connected with the ICCD (7), for controlling the acquisition delay of the ICCD (7).

3. A polarized LIBS-LIF system for trace element detection as claimed in claim 2, wherein, The analysis control module further comprises a computer (9) connected with the optical parametric oscillator (2) and the ICCD (7) respectively, for controlling the output wavelength of the optical parametric oscillator (2), and for analyzing the plasma spectrum signal acquired by the ICCD (7) and displaying the spectrum image.

4. A polarized LIBS-LIF system for trace element detection as claimed in claim 2, wherein, the laser pulse emission delay between the first and second laser beams is at least 10 The wavelength range of the optical parametric oscillator (2) is 251.51nm-251.71nm. .

5. A polarized LIBS-LIF system for trace element detection as claimed in claim 1, wherein, The wavelength of the optical parametric oscillator (2) is 251.61nm.

6. A polarized LIBS-LIF system for trace element detection as claimed in claim 5, wherein, The polarizer (15) can be rotated to a specific angle to remove the spectral background of the element to be measured.

7. A polarized LIBS-LIF system for trace element detection as claimed in claim 1, wherein, ​

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