Fiber grating and LIBS based specific element concentration measuring device and measuring method

Abstract

This invention belongs to the field of spectroscopic technology for sample composition and content analysis, specifically relating to a device and method for measuring the concentration of specific elements based on fiber Bragg gratings and LIBS. A solid-state Q-switched laser emits pulsed light that interacts with the substance through an optical path. The resulting plasma is transmitted to corresponding single-mode fibers, circulators, and corresponding gratings, then returns to the circulator and is fed into the corresponding detector. A timing controller controls the light intensity collected by the detector for integration calculation, and the result is returned to a computer. The wavelengths selected by the first and second fiber Bragg gratings correspond to the internal standard element and the analyte element in the sample, respectively. Using the ratio of the corresponding light intensities and the mathematical relationship established with the standard sample, the concentration of the analyte element in the unknown sample can be calculated. This invention eliminates the need for a complex spectrometer structure, resulting in a simple device structure, high resolution for single-element concentration measurement, and allows for control of the fiber Bragg grating wavelength within 100 pm using a temperature-controlled water bath, or the measurement of different element concentrations by replacing the fiber Bragg grating with different wavelengths.

Description

Technical Field

[0001] This invention belongs to the field of spectroscopic technology for sample composition and content analysis, specifically relating to a device and method for measuring the concentration of specific elements based on fiber optic gratings and LIBS. Background Technology

[0002] Laser-induced breakdown spectroscopy (LIBS) uses pulsed lasers (typically tens to hundreds of millijoules) to excite plasma on the sample surface, then uses spectroscopic analysis equipment to extract spectral information of atoms, ions, and molecules from the plasma for qualitative and quantitative analysis. Its advantages include no need for complex sample pretreatment, strong telemetry capabilities, high sensitivity for multi-element detection, and the ability to analyze heavy, light, and even trace elements. With advancements in spectrometers, detectors, and data processing technologies, the sensitivity, accuracy, and repeatability of LIBS have improved. Currently, there has been considerable research and application of LIBS in alloys, rocks, fossil fuels, environmental protection, and food safety.

[0003] When using laser-induced breakdown spectroscopy (LIBS) to measure sample concentration, the spectrometer's resolution, detector performance, and system response speed all significantly impact the quantitative analysis capability of LIBS elements. High spectral resolution improves the identification and measurement of elemental spectral lines, contributing to a higher spectral signal-to-noise ratio and thus enhancing the accuracy of target element analysis. High-sensitivity and high-dynamic-range detectors can identify and measure spectral lines with significant intensity differences, further improving the quantitative analysis capabilities of LIBS. To fully capture the transient signals emitted by LIBS plasma, the spectrometer requires a fast response time and high-speed data acquisition capabilities. Furthermore, environmental temperature and humidity affect the spectrometer. Because spectrometers contain complex optical and electronic components, temperature changes can alter parameters such as wavelength calibration, detector dark current, and noise levels. High humidity can cause fogging of components like optical windows, spectroscopes, and lenses, reducing signal transmission efficiency. Appropriately controlling the humidity of the experimental environment helps ensure stable spectrometer operation and experimental accuracy. With increased usage time, spectrometers may experience optical component aging, detector performance degradation, and decreased system stability. Optical components such as lenses, spectroscopes, and optical windows can age, corrode, or deform due to prolonged exposure to strong light, dust, and environmental chemicals, thus affecting the spectrometer's performance. Therefore, to ensure the accuracy and repeatability of LIBS experiments, regular maintenance and calibration of the spectrometer, maintaining a stable experimental environment, and timely replacement of aging and damaged optical components and detectors are crucial.

[0004] Therefore, in existing LIBS methods for measuring sample concentration, the overlap of emission lines from individual elements in the spectrum can lead to peak broadening and peak aliasing, making quantitative measurement of elemental concentration difficult. Environmental factors such as light, dust, and gases can interfere with the propagation and detection of the LIBS signal, resulting in inaccurate elemental measurements. Furthermore, changes in spectrometer components (e.g., gratings, detectors) over time and with use can cause problems such as increased peak width, decreased signal-to-noise ratio, or wavelength drift. These issues degrade the LIBS signal quality, thus affecting the accuracy and precision of LIBS quantitative analysis. Therefore, the resolution of elemental spectra, the stability of the spectrometer, and the experimental environment have a significant impact on the accuracy of LIBS measurements of sample concentration.

[0005] A fiber grating (FBG) is a diffraction grating formed by periodically modulating the refractive index of an optical fiber core using a specific method. It is a passive filtering device. The main fabrication method of FBG utilizes the photosensitivity of the optical fiber material. A coherent field pattern of the incident light is written into the fiber core using ultraviolet light exposure, creating a periodic change in refractive index along the fiber core axis, thus forming a permanent spatial phase grating. Essentially, it acts as a narrow-band (transmission or reflection) filter or mirror within the fiber core. When a broadband beam of light passes through the FBG, wavelengths that satisfy the FBG Bragg condition are reflected, while the remaining wavelengths continue to propagate through the FBG. Because FBG fibers have advantages such as small size, low splice loss, full compatibility with optical fibers, and the ability to embed smart materials, and because their resonant wavelengths are sensitive to changes in external environments such as temperature, strain, refractive index, and concentration, they are widely used in the fabrication of fiber lasers, fiber optic communication, and sensing. In existing technologies, when using fiber Bragg grating sensors to directly detect the elemental concentration of solid samples, the inherent diffraction grating principle makes them sensitive to reflectivity during the detection process. Changes in the surface reflectivity of the solid material being measured can lead to shifts in the sensor's output signal and a decrease in accuracy. Furthermore, the operational stability of fiber Bragg grating sensors is significantly affected by temperature variations. When the temperature changes, the sensor's sensitivity and accuracy may fluctuate or drift, thus affecting the accuracy of the measurement results. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a device and method for measuring the concentration of specific elements based on fiber Bragg grating laser-induced breakdown spectroscopy, thereby solving the problems of poor elemental spectral resolution and environmental interference in traditional element concentration measurements, and achieving accurate, stable, and efficient concentration measurement.

[0007] This invention is achieved through the following technical solution:

[0008] A specific element concentration measurement device based on fiber Bragg gratings and LIBS, the measurement device comprising:

[0009] Solid-state Q-switched lasers are used to emit laser beams;

[0010] A timing controller, connected to the solid-state Q-switched laser, is used to control the operating timing of the solid-state Q-switched laser;

[0011] A plane mirror, a first focusing lens, and a sample are arranged sequentially along the optical path of the laser beam. The plane mirror reflects the laser beam emitted by the solid-state Q-switched laser onto the first focusing lens. After being focused by the first focusing lens, the laser beam emitted by the solid-state Q-switched laser interacts with the sample to generate plasma. The light waves generated by the plasma include reference light and probe light.

[0012] The reference detection unit includes a second focusing lens, a first single-mode fiber, a first circulator, a first fiber grating, and a first photodetector. The reference light is focused by the second focusing lens onto the end face of the first single-mode fiber located at the focal point, then passes through the first circulator into the first fiber grating, and returns to the first circulator after passing through the first fiber grating, entering the first photodetector.

[0013] The measurement and detection unit includes a third focusing lens, a second single-mode fiber, a second circulator, a second fiber grating, and a second photodetector. The detection light is focused by the third focusing lens onto the end face of the second single-mode fiber located at the focal point, then passes through the second circulator into the second fiber grating, returns to the second circulator after passing through the second fiber grating, and enters the second photodetector.

[0014] The first photodetector is connected to the timing controller and the computer via a first detector control circuit; the second photodetector is connected to the timing controller and the computer via a second detector control circuit.

[0015] The computer integrates the light intensity signals collected by the first and second photodetectors controlled by the timing controller, and saves the calculation results to the computer. The relative concentration of the element to be measured in the sample is obtained by using the ratio of the light intensity of the reference element to the light intensity of the element to be measured.

[0016] Furthermore, the first fiber grating is entirely located in the first constant temperature water bath or semiconductor cooler (TEC), and the second fiber grating is entirely located in the second constant temperature water bath or semiconductor cooler (TEC).

[0017] Furthermore, the plane of the sample is positioned at the focal point of the first focusing lens; the end face of the first single-mode fiber is positioned at the focal point of the second focusing lens, and the end face of the second single-mode fiber is positioned at the focal point of the third focusing lens;

[0018] The size of the first focusing lens is such that the entire laser beam of the solid-state Q-switched laser can pass through it.

[0019] Furthermore, the applicable wavelengths of the first single-mode fiber, the first circulator, the first fiber grating, and the first photodetector in the reference detection unit are determined by the wavelength of the light excited by the reference element.

[0020] The applicable wavelengths of the second single-mode fiber, the second circulator, the second fiber grating, and the second photodetector in the measurement and detection unit are determined by the wavelength of the light generated by the excitation of the reference element.

[0021] Furthermore, the first single-mode optical fiber is connected to the first circulator, the first circulator is connected to the first fiber grating and the first photodetector, and the first photodetector is connected to the timing controller and the computer through the first detector control circuit;

[0022] The second single-mode fiber is connected to the second circulator, and the second circulator, the second fiber grating, and the second photodetector are connected; the second photodetector is connected to the timing controller and the computer through the second detector control circuit.

[0023] Furthermore, the frequency and timing of the pulsed beam emitted by the solid-state Q-switched laser, the start and end integration times of the light intensity signal received by the first photodetector, and the start and end times of the light intensity signal received by the second photodetector are all controlled by the timing controller.

[0024] A method for measuring the concentration of a specific element based on fiber Bragg gratings and LIBS, the method comprising:

[0025] A solid-state Q-switched laser emits a laser beam under the control of a timing controller. The laser beam is focused onto the surface of the sample under test by a first focusing lens. The high-energy pulsed laser beam interacts with the sample to generate plasma. The plasma generates reference light and probe light.

[0026] The reference light is coupled to the first single-mode fiber through the second focusing lens, transmitted to the first optical circulator through the first single-mode fiber, and then enters the first fiber grating through the first circulator. After being reflected and filtered by the first fiber grating, it returns to the first circulator and then enters the first photodetector through the first circulator.

[0027] The probe light is coupled to the second single-mode fiber through the third focusing lens, transmitted to the second optical circulator through the second single-mode fiber, and then enters the second fiber grating through the second circulator. After being reflected and filtered by the second fiber grating, it returns to the second circulator and then enters the second photodetector through the second circulator.

[0028] The computer integrates the light intensity signals collected by the first and second photodetectors controlled by the timing controller, and saves the calculation results to the computer. The relative concentration of the element to be measured in the sample is obtained by using the ratio of the light intensity of the reference element to the light intensity of the element to be measured.

[0029] Furthermore, the LIBS spectra received by the first and second photodetectors are displayed in real time on a computer, and the type of the element to be measured is determined by searching the NIST database.

[0030] Furthermore, the first fiber grating is entirely located in the first constant temperature water bath or semiconductor cooler, and the second fiber grating is entirely located in the second constant temperature water bath or semiconductor cooler.

[0031] By changing the temperature values ​​of the first constant temperature water bath, the second constant temperature water bath, or the semiconductor cooler TEC, or by changing the wavelength values ​​of the first fiber grating and the second fiber grating, the concentration values ​​of different elements to be measured can be calculated.

[0032] Furthermore, in the qualitative analysis of a single LIBS spectrum, the characteristic spectral intensity corresponding to the analyte is expressed as:

[0033]

[0034] Among them, I ij The integral represents the spectral line intensity; i and j represent the upper and lower energy levels of the transition line, respectively; n s Indicates the number of atoms or ion number density of the element to be measured; A ij G is represented as the transition probability; i Indicates statistical weight; U s (T) represents the partition function; E i The excited state energy is represented by T, the plasma temperature by k, and the Boltzmann constant by k. F is an experimental constant. The intensity of the spectral line corresponding to the element being measured is proportional to the element content.

[0035] Beneficial technical effects of the present invention:

[0036] (1) The measuring device provided by the present invention does not require a complex spectrometer. It only requires two photodetectors to measure the light intensity corresponding to the reference wavelength element and the light intensity corresponding to the element to be measured, respectively, to realize the measurement of the concentration of the element to be measured.

[0037] (2) The measuring device provided by the present invention has a simple structure, is less affected by the surrounding environment, has high resolution for single element concentration measurement, and can also control the fiber grating wavelength within 100 pm by changing the temperature of the constant temperature water bath (or semiconductor cooler TEC), or replace the fiber grating with different wavelengths to measure the concentration of different elements in the sample to be tested.

[0038] (3) The measurement device provided by the present invention has a lower cost than the laser-induced breakdown spectroscopy measurement system composed of commonly used spectrometers. Furthermore, by using a standard sample with a known concentration as a reference for calibration, possible signal offsets can be corrected. This can transform actual measurements into relative measurements, reduce the influence of surface reflectivity changes, and enable the measurement device provided by the present invention to be used for the detection of solid samples without producing output signal offset problems, thus achieving high detection accuracy.

[0039] (4) The measurement method provided by the present invention, through fiber optic grating combined with LIBS technology, can achieve a more compact, stable and efficient spectral measurement solution in the field of element concentration determination. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure of a specific element concentration measurement device based on fiber Bragg gratings and LIBS in an embodiment of the present invention.

[0041] Figure 2 This is a flowchart of a method for measuring the concentration of specific elements based on fiber Bragg gratings and LIBS.

[0042] Reference numerals: 1: Solid-state Q-switched laser; 2: Timing controller; 3: First detector control circuit; 4: Second detector control circuit B; 5: First photodetector; 6: Second photodetector; 7: First circulator; 8: Second circulator; 9: First fiber grating; 10: Second fiber grating; 11: First constant temperature water bath; 12: Second constant temperature water bath; 13: Plane mirror; 14: First focusing lens; 15: Second focusing lens; 16: Third focusing lens; 17: First single-mode fiber; 18: Second single-mode fiber; 19: Sample stage; 20: Sample; 21: Computer. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0044] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0045] like Figure 1 As shown, the present invention provides a specific element concentration measurement device based on fiber Bragg gratings and LIBS, the measurement device comprising:

[0046] A solid-state Q-switched laser for emitting a laser beam; specifically, the solid-state Q-switched laser is an electro-optic active Q-switched laser.

[0047] A timing controller (specifically, a DG535 model) is connected to the solid-state Q-switched laser and is used to control the operating timing of the solid-state Q-switched laser.

[0048] A planar reflector, a first focusing lens, and a sample (set on a sample stage) are sequentially arranged along the optical path of the laser beam. The planar reflector reflects the laser beam emitted by the solid-state Q-switched laser onto the first focusing lens. The laser beam emitted by the solid-state Q-switched laser, after being focused by the first focusing lens, interacts with the sample to generate plasma. The light waves generated by the plasma include reference light and probe light. Under the action of high-energy laser, the sample surface absorbs photon energy, melts, evaporates, and sputters a small number of sample particles. The sample particles rapidly expand along the normal direction of the sample surface, forming a high-temperature plasma region. In this embodiment, the focal length can be adjusted by adjusting the position of the first focusing lens to achieve the measurement of elemental concentrations of samples at different distances. Due to the collision of particles in the high-temperature system, atomic ions are distributed to different energy levels. Particles at high energy levels are prone to transitions and emit strong spectral lines. The light emitted by the generated plasma is coupled to the first single-mode fiber and the second single-mode fiber through the second and third focusing lenses, respectively.

[0049] The reference detection unit includes a second focusing lens, a first single-mode fiber, a first circulator, a first fiber grating, and a first photodetector. The reference light is focused by the second focusing lens onto the end face of the first single-mode fiber at the focal point, then passes through the first circulator into the first fiber grating. After passing through the first fiber grating, the light returns to the first circulator and enters the first photodetector. The focal length is adjusted by adjusting the position of the first focusing lens to measure the elemental concentration of samples at different distances. Due to the collision of particles in the high-temperature system, atomic ions are distributed to different energy levels. Particles at higher energy levels are prone to transitions and emit strong spectral lines.

[0050] The measurement and detection unit includes a third focusing lens, a second single-mode fiber, a second circulator, a second fiber grating, and a second photodetector. The detection light is focused by the third focusing lens onto the end face of the second single-mode fiber located at the focal point, then passes through the second circulator into the second fiber grating, returns to the second circulator after passing through the second fiber grating, and enters the second photodetector.

[0051] The light intensity collected by the detector is integrated by the timing controller, and the calculation result is returned to the computer. The relative concentration of the element to be measured in the sample can be obtained by using the ratio of the light intensity of the internal standard element to the light intensity of the element to be measured.

[0052] Specifically, the first single-mode fiber is connected to the first circulator, the first circulator is connected to the first fiber grating and the first photodetector, the second single-mode fiber is connected to the second circulator, and the second circulator, the second fiber grating, and the second photodetector are connected. The first photodetector is connected to the timing controller and the computer via a first detector control circuit; the second photodetector is connected to the timing controller and the computer via a second detector control circuit, wherein both the first and second detector control circuits are conventional detector control circuits.

[0053] In this embodiment, the first fiber grating is entirely located in the first constant temperature water bath or semiconductor cooler (TEC), and the second fiber grating is entirely located in the second constant temperature water bath or semiconductor cooler (TEC).

[0054] In this embodiment, the plane of the sample is positioned at the focal point of the first focusing lens; the end face of the first single-mode fiber is positioned at the focal point of the second focusing lens, and the end face of the second single-mode fiber is positioned at the focal point of the third focusing lens.

[0055] In this embodiment, the first, second, and third focusing lenses are all convex lenses, and the focal positions of the first, second, and third focusing lenses are known; the sizes of the second and third focusing lenses are fixed. The size of the first focusing lens is such that the entire laser beam of the solid-state Q-switched laser passes through it.

[0056] In this embodiment, the applicable wavelengths of the first single-mode fiber, the first circulator, the first fiber grating, and the first photodetector in the reference detection unit are determined by the wavelength of the light generated by the excitation of the reference element.

[0057] The applicable wavelengths of the second single-mode fiber, the second circulator, the second fiber grating, and the second photodetector in the measurement and detection unit are determined by the wavelength of the light generated by the excitation of the measuring element.

[0058] In this embodiment, the frequency and timing of the pulsed beam emitted by the solid-state Q-switched laser, the start and end times of the integration of the light intensity signal received by the first photodetector, and the start and end times of the integration of the light intensity signal received by the second photodetector are all controlled by the timing controller. Specifically, to lock the generation time of the plasma effective laser-induced breakdown spectrum, the trigger signal of the excitation pulse light emitted by the laser is delayed by the timing controller for a certain time (typically 500ns), and then a TTL high-level signal is given as an external trigger signal to trigger the photodetector to collect data.

[0059] This invention also provides a method for measuring the concentration of specific elements based on fiber gratings and LIBS, such as... Figure 2 As shown, the method is as follows: a solid-state Q-switched laser emits pulsed light that interacts with the sample through an optical path. The resulting plasma is transmitted to the corresponding single-mode fiber, circulator, and corresponding grating, and then returns to the circulator and is transmitted to the corresponding detector. The timing controller controls the light intensity collected by the detector to perform integration calculation, and the result is returned to the computer. The wavelengths selected by the first and second fiber gratings correspond to the internal standard element and the element to be measured in the analyte, respectively. Using the ratio of the corresponding light intensities and the mathematical relationship established with the standard sample, the concentration of the element to be measured in the unknown sample can be calculated.

[0060] The measurement method is specifically as follows:

[0061] A solid-state Q-switched laser emits a laser beam under the control of a timing controller. The laser beam is focused onto the surface of the sample under test by a first focusing lens. The high-energy pulsed laser beam interacts with the sample to generate plasma. The plasma generates reference light and probe light.

[0062] The reference light is coupled to the first single-mode fiber through the second focusing lens, transmitted to the first optical circulator through the first single-mode fiber, and then enters the first fiber grating placed in the first constant temperature water bath or semiconductor cooler through the first circulator. After being reflected and filtered by the first fiber grating, it returns to the first circulator and then enters the first photodetector through the first circulator.

[0063] The probe light is coupled to the second single-mode fiber through the third focusing lens, and then transmitted to the second optical circulator through the second single-mode fiber. It then enters the second fiber grating placed in the second constant temperature water bath or semiconductor cooler through the second circulator. After being reflected and filtered by the second fiber grating, it returns to the second circulator and then enters the second photodetector through the second circulator.

[0064] The time-series controller integrates the light intensity collected by the detector, and the result is returned to the computer. Using the ratio of corresponding light intensities and the mathematical relationship established with the standard sample, the concentration of the analyte in the unknown sample is calculated. In other words, the relative concentration of the analyte in the sample can be obtained by using the ratio of the light intensity of the internal standard element to that of the analyte.

[0065] In this system, the wavelength selected by the first fiber grating corresponds to the internal standard element (i.e., reference element) in the analyte (determined by the NIST standard database), while the wavelength of the second fiber grating corresponds to the element to be measured in the analyte. Using the ratio of the light intensity corresponding to the element to be measured to the internal standard element (i.e., reference element) and the mathematical relationship established with the standard sample, the concentration of the element to be measured in the unknown sample can be calculated.

[0066] In this embodiment, the LIBS spectra received by the first photodetector and the second photodetector are displayed in real time on a computer, and the type of the element to be measured is determined by searching the NIST database.

[0067] In this embodiment, the wavelength of the fiber optic grating can be controlled within 100 pm by changing the temperature value of the first constant temperature water bath, the second constant temperature water bath, or the semiconductor cooler TEC; or different element concentrations can be measured by replacing the fiber optic grating with a different wavelength.

[0068] In this embodiment, when performing qualitative analysis on a single LIBS spectrum, it can be approximated as being in a state of local thermal equilibrium, and the self-absorption effect can be ignored; the characteristic spectral intensity corresponding to the analyte is expressed as:

[0069]

[0070] Among them, I ij The integral represents the spectral line intensity; i and j represent the upper and lower energy levels of the transition line, respectively; n s Indicates the number of atoms or ion number density of the element to be measured; A ijG is represented as the transition probability; i Indicates statistical weight; U s (T) represents the partition function; E i The excited state energy is represented by T, the plasma temperature by k, and the Boltzmann constant by k. F is an experimental constant. The intensity of the spectral line corresponding to the element being measured is proportional to the element content.

[0071] Among them, except for n s In addition, all parameters can be approximated as constants; the corresponding spectral line intensities can be approximated as being proportional to the element content, and the same element corresponding to the same wavelength has a certain degree of comparability between different samples.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A specific element concentration measurement device based on fiber Bragg gratings and LIBS, characterized in that, The measuring device includes: Solid-state Q-switched lasers are used to emit laser beams; A timing controller, connected to the solid-state Q-switched laser, is used to control the operating timing of the solid-state Q-switched laser; A plane mirror, a first focusing lens, and a sample are arranged sequentially along the optical path of the laser beam. The plane mirror reflects the laser beam emitted by the solid-state Q-switched laser onto the first focusing lens. After being focused by the first focusing lens, the laser beam emitted by the solid-state Q-switched laser interacts with the sample to generate plasma. The light waves generated by the plasma include reference light and probe light. The reference detection unit includes a second focusing lens, a first single-mode fiber, a first circulator, a first fiber grating, and a first photodetector. The reference light is focused by the second focusing lens onto the end face of the first single-mode fiber, then passes through the first circulator into the first fiber grating, returns to the first circulator after passing through the first fiber grating, and enters the first photodetector. The measurement and detection unit includes a third focusing lens, a second single-mode fiber, a second circulator, a second fiber grating, and a second photodetector. The detection light is focused by the third focusing lens onto the end face of the second single-mode fiber, then passes through the second circulator into the second fiber grating, returns to the second circulator after passing through the second fiber grating, and enters the second photodetector. The first photodetector and the timing controller and computer are connected; the second photodetector and the timing controller and computer are connected ； The computer integrates the light intensity signals collected by the first photodetector and the second photodetector, and saves the calculation results to the computer. The relative concentration of the element to be measured in the sample is obtained by using the ratio of the light intensity of the reference element to the light intensity of the element to be measured.

2. The specific element concentration measurement device based on fiber optic grating and LIBS according to claim 1, characterized in that, The first fiber grating is entirely located in the first constant temperature water bath or semiconductor cooler, and the second fiber grating is entirely located in the second constant temperature water bath or semiconductor cooler.

3. The specific element concentration measurement device based on fiber optic gratings and LIBS according to claim 1, characterized in that, The plane of the sample is positioned at the focal point of the first focusing lens; the end face of the first single-mode fiber is positioned at the focal point of the second focusing lens, and the end face of the second single-mode fiber is positioned at the focal point of the third focusing lens. The size of the first focusing lens is such that the entire laser beam of the solid-state Q-switched laser can pass through it.

4. The specific element concentration measurement device based on fiber optic grating and LIBS according to claim 1, characterized in that, The applicable wavelengths of the first single-mode fiber, the first circulator, the first fiber grating, and the first photodetector in the reference detection unit are determined by the wavelength of the light excited by the reference element. The applicable wavelengths of the second single-mode fiber, the second circulator, the second fiber grating, and the second photodetector in the measurement and detection unit are determined by the wavelength of the light generated by the element to be measured.

5. The specific element concentration measurement device based on fiber optic grating and LIBS according to claim 1, characterized in that, The first single-mode fiber is connected to the first circulator, the first circulator is connected to the first fiber grating and the first photodetector, and the first photodetector is connected to the timing controller and the computer through a first detector control circuit. The second single-mode fiber is connected to the second circulator, and the second circulator is connected to the second fiber grating and the second photodetector; the second photodetector is connected to the timing controller and the computer through the second detector control circuit.

6. The specific element concentration measurement device based on fiber optic grating and LIBS according to claim 5, characterized in that, The frequency and timing of the pulsed beam emitted by the solid-state Q-switched laser, the start and end times of the integration of the light intensity signal received by the first photodetector, and the start and end times of the integration of the light intensity signal received by the second photodetector are all controlled by the timing controller.

7. A method for measuring the concentration of a specific element based on fiber Bragg gratings and LIBS, characterized in that, The measurement method includes: A solid-state Q-switched laser emits a laser beam under the control of a timing controller. The laser beam is focused onto the surface of the sample under test by a first focusing lens. The high-energy pulsed laser beam interacts with the sample to generate plasma, and the plasma generates reference light and probe light. The reference light is coupled to the first single-mode fiber through the second focusing lens, transmitted to the first optical circulator through the first single-mode fiber, and then enters the first fiber grating through the first circulator. After being reflected and filtered by the first fiber grating, it returns to the first circulator and then enters the first photodetector through the first circulator. The probe light is coupled to the second single-mode fiber through the third focusing lens, transmitted to the second optical circulator through the second single-mode fiber, and then enters the second fiber grating through the second circulator. After being reflected and filtered by the second fiber grating, it returns to the second circulator and then enters the second photodetector through the second circulator. The computer integrates the light intensity signals collected by the first and second photodetectors, saves the calculation results to the computer, and uses the ratio of the light intensity of the reference element to the light intensity of the element to be measured to obtain the relative concentration of the element to be measured in the sample.

8. The method for measuring specific element concentration based on fiber optic gratings and LIBS according to claim 7, characterized in that, The LIBS spectra received by the first and second photodetectors are displayed in real time on a computer, and the types of elements to be measured are determined by searching the NIST database.

9. The method for measuring specific element concentration based on fiber optic gratings and LIBS according to claim 7, characterized in that, The first fiber grating is completely located in the first constant temperature water bath or semiconductor cooler, and the second fiber grating is completely located in the second constant temperature water bath or semiconductor cooler. By changing the temperature values ​​of the first constant temperature water bath, the second constant temperature water bath, or the semiconductor cooler, or by changing the wavelength values ​​of the first fiber grating or the second fiber grating, the concentration values ​​of different elements to be measured can be calculated.

10. The method for measuring specific element concentration based on fiber optic gratings and LIBS according to claim 7, characterized in that, When performing qualitative analysis on a single LIBS spectrum, the characteristic spectral intensity corresponding to the analyte is expressed as: Among them, I ij The integral represents the spectral line intensity; i and j represent the upper and lower energy levels of the transition line, respectively; n s Indicates the number of atoms or ion number density of the element to be measured; A ij G is represented as the transition probability; i Indicates statistical weight; U s (T) represents the partition function; E i The excited state energy is represented by T, the plasma temperature by k, and the Boltzmann constant by k. F is an experimental constant. The intensity of the spectral line corresponding to the element being measured is proportional to the element content.

Images