Optical fiber type laser-induced breakdown spectroscopy system and method applied to underwater environment detection

Abstract

The invention discloses an optical fiber type laser-induced breakdown spectroscopy system and method applied to underwater environment detection, the system comprises an optical fiber LIBS main body system, a gas pipe-optical fiber coupling system and an underwater LIBS probe, the optical fiber LIBS main body system comprises a laser emitting assembly and a gas conveying assembly; the air pipe-optical fiber coupling system comprises an air inlet pipe interface, a special optical fiber interface, an air outlet pipe and an air outlet pipe interface; the underwater LIBS probe comprises a trachea optical fiber coupling interface, a focusing lens group and a front end opening. According to the invention, a micro-gas environment is created in an underwater environment and a plasma emission spectrum signal is obtained, and a small-sized LIBS probe can enter a narrow area and detect radioactive foreign matters, so that main equipment and operators can be far away from a high-radioactivity environment; obvious characteristic spectral lines can be obtained, so that the element types and contents of the to-be-detected sample are accurately analyzed, the repeatability is high, the spectral signal-to-noise ratio is high, the analysis speed is high, and the measurement process is safe and reliable.

Description

Technical Field

[0001] The invention belongs to the technical field of laser diagnosis, and in particular relates to an optical fiber laser induced breakdown spectroscopy system and method applied to underwater environment detection. Background Art

[0002] Radioactive items that need to be tested in nuclear power plants are usually placed in boron water. Due to their high radioactivity, when their elemental composition needs to be tested, conventional testing methods require samples to be transported to the laboratory for testing, which takes a long time and seriously affects the maintenance process of nuclear power plants in actual testing scenarios, causing economic losses; on-site testing methods such as X-ray fluorescence technology are affected by the radioactivity of the items to be tested, and accuracy is difficult to guarantee. At the same time, radioactive foreign matter will also pose a health threat to on-site testing personnel.

[0003] Laser-induced breakdown spectroscopy (LIBS) is a technique that uses pulsed laser focusing to ablate the sample surface to form plasma, analyzes the emission spectrum during the plasma evolution process, and quantitatively analyzes the elemental composition of the sample to be tested. Compared with other technologies, the advantages of LIBS technology include minimal sample damage, no sample pretreatment, and the ability to analyze multiple elements simultaneously.

[0004] However, the underwater LIBS devices that have been developed have the following shortcomings: Patents CN118130432A and CN111912831A propose to create a micro-atmosphere environment underwater to avoid plasma quenching, but the main LIBS equipment such as lasers and spectrometers are placed in the underwater environment, and the probe is too large, which is not conducive to adjusting the relative position with underwater manipulators such as robotic arms. At the same time, the LIBS system including lasers and spectrometers in the probe is too close to highly radioactive foreign objects, which will damage the equipment and is not suitable for the radioactive environment of nuclear power plants and small detection scenarios. Summary of the invention

[0005] The first purpose of the present invention is to solve the problems in the prior art and provide an underwater LIBS detection system for radioactive foreign matter in nuclear power plants. By transmitting laser through optical fiber-laser and special optical fiber, the part of the LIBS system close to the sample is a pure optical path, and important electrical equipment can be placed in a safe area. Using an underwater robot equipped with a LIBS probe to detect foreign matter close to the foreign matter can prevent the equipment from approaching the radioactive foreign matter and reduce the risk to personnel.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A fiber-optic laser induced breakdown spectroscopy (LIBS) system for underwater environment detection, comprising:

[0008] Fiber LIBS main system, air tube-fiber coupling system and underwater LIBS probe;

[0009] The optical fiber LIBS main system includes a laser emission component and a gas delivery component; the laser emission component includes a laser, a fine-adjustable focal length lens, an optical fiber coupler and a first flexible optical fiber connected in sequence; the gas delivery component includes a gas cylinder and an air pipe connected to the gas cylinder; the air pipe-optical fiber coupling system includes an air inlet pipe interface, a special optical fiber interface, an air outlet pipe and an air outlet pipe interface; the underwater LIBS probe includes an air pipe optical fiber coupling interface, a focusing lens group, and a front end opening;

[0010] The laser is used to emit laser light, the finely adjustable focal length lens is used to control the laser coupling efficiency, the fiber coupler is used to feed the laser light emitted by the laser into the flexible optical fiber to form a special optical fiber, one end of the special optical fiber is connected to the special optical fiber interface, and the other end of the air pipe is connected to the air inlet pipe interface;

[0011] The trachea-fiber coupling system is used to couple the special optical fiber into the trachea outlet, and output it through the trachea outlet interface and connect it to the trachea fiber coupling interface;

[0012] The focusing lens group is used to focus the laser fed from the special optical fiber to the front end opening and generate plasma.

[0013] Furthermore, the laser and the fine-adjustable focal length lens also include a polarizer, an attenuator and a spectroscope connected in sequence, a photodiode is connected below the spectroscope, and the laser is sampled by the spectroscope and converted into an electrical signal by the photodiode.

[0014] Furthermore, the laser coupling efficiency is controlled by adjusting the relative position between the finely adjustable focal length lens and the first flexible optical fiber.

[0015] Furthermore, the fiber LIBS main system also includes a plasma luminescence transmission component, which includes a spectrometer, a plasma luminescence transmission fiber, a second flexible fiber, a timing control trigger and a controller; the spectrometer is connected to the plasma luminescence transmission fiber and the timing control trigger respectively, the plasma luminescence transmission fiber is connected to the second flexible fiber, the second flexible fiber is connected to the special fiber, and the timing control trigger is connected to the controller.

[0016] Furthermore, the special optical fiber interface is sealed with filler.

[0017] Furthermore, the special optical fiber consists of one main optical fiber and multiple branch optical fibers, the main optical fiber is used to transmit laser, the branch optical fibers are used to transmit plasma luminescence, and the branch optical fibers are tightly arranged around the main optical fiber on an end face with a diameter of 2 mm.

[0018] Furthermore, the underwater LIBS probe also includes a gas buffer chamber, and two ends of the gas buffer chamber are respectively connected to the air tube optical fiber coupling interface and the front end opening.

[0019] Furthermore, the underwater LIBS probe also includes a check valve, which is arranged between the gas buffer chamber and the front end opening.

[0020] Furthermore, the controller is signal-connected to the gas cylinder and the laser.

[0021] A second object of the present invention is to provide an underwater environment detection method using the above system, comprising the following steps:

[0022] Step (1), adjusting the laser emission component until the optical fiber feed energy fluctuation is stable;

[0023] Step (2), mounting the underwater LIBS probe on the underwater robot arm, and manipulating the underwater robot arm to reach the foreign object location;

[0024] Step (3), the controller controls the gas control valve to adjust the flow rate so that a preset gas environment is formed at the front end of the probe;

[0025] Step (4), the controller outputs a signal to control the laser to emit laser light, which is transmitted to the underwater LIBS probe via the special optical fiber main optical fiber, and is focused on the foreign matter in the gas environment by the focusing lens group to generate plasma. The plasma light is transmitted back to the spectrometer by the special optical fiber sub-fiber, and the controller outputs a signal to control the spectrometer to collect the plasma light to obtain a spectrum.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention couples laser and optical fiber to obtain special optical fiber, and then couples the special optical fiber into the trachea to protect the special optical fiber. The laser is transmitted through the special optical fiber. The part close to the sample to be detected is a pure optical system, and the rest can be placed in a safe area on the shore, which can prevent the equipment from approaching radioactive foreign matter. The LIBS detection result is not affected by the radioactive environment, and people are prevented from being exposed to the radioactive environment. The laser and plasma light are transmitted back through a long special optical fiber to prevent major equipment such as lasers and spectrometers from being damaged by highly radioactive foreign matter. The probe is designed to be small in size and suitable for small space scenes.

[0028] The method of the present invention can obtain obvious characteristic spectral lines to accurately analyze the element types and contents of the sample to be tested, has high repeatability, high spectral signal-to-noise ratio, fast analysis speed, and a safe and reliable measurement process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1This is the overall structure diagram of the fiber-based laser-induced breakdown spectroscopy (LIBS) system for underwater environment detection;

[0030] Figure 2 This is the structure diagram of the air tube-fiber coupling system of the fiber LIBS detection device;

[0031] Figure 3 This is the structure diagram of the underwater LIBS probe of the optical fiber LIBS detection device;

[0032] Figure 4 This is the flow chart of underwater environment detection operation of optical fiber LIBS detection device;

[0033] Figure 5 This is the spectrum of the optical fiber LIBS detection device for target detection of underwater alloy steel samples;

[0034] In the figure: 100, optical fiber LIBS main system; 200, air tube-optical fiber coupling system; 300, underwater LIBS probe; 1, laser; 2, polarizer; 3, attenuator; 4, photodiode; 5, spectroscope; 6, fine-tunable focusing lens; 7, optical fiber coupler; 8, first flexible optical fiber; 9, controller; 10, timing control trigger; 11, spectrometer; 12, plasma luminescence transmission optical fiber; 13, second flexible optical fiber; 14, special optical fiber; 15, gas cylinder; 16, gas control valve; 17, air tube; 18, air inlet pipe interface; 19, special optical fiber interface; 20, air outlet pipe; 21, air outlet pipe interface; 22, air tube interface; 23, coupling optical fiber interface; 24, check valve; 25, focusing lens group; 26, gas buffer chamber; 27, front end opening. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with embodiments and drawings.

[0036] like Figure 1 As shown, the present invention provides a fiber laser induced breakdown spectroscopy (LIBS) system for underwater environment detection, including a fiber LIBS main system 100, an air tube-fiber coupling system 200 and an underwater LIBS probe 300;

[0037] The fiber LIBS main system 100 includes a laser emission component, a gas delivery component and a plasma luminescence transmission component; the laser emission component includes a laser 1, a polarizer 2, an attenuator 3, a spectroscope 5, a fine-adjustable focal length lens, a fiber coupler 7 and a first flexible optical fiber 8 connected in sequence, and a photodiode 4 is connected below the spectroscope 5; the gas delivery component includes a gas cylinder 15 and a gas pipe 17 connected to the gas cylinder 15, and a gas control valve 16 is provided at the opening of the gas cylinder 15; the plasma luminescence transmission component includes a spectrometer 11, a plasma luminescence transmission optical fiber 12, a second flexible optical fiber 13, a time The spectrometer 11 is connected to the plasma luminescence transmission fiber 12 and the timing control trigger 10 respectively, the plasma luminescence transmission fiber 12 is connected to the second flexible optical fiber 13, the second flexible optical fiber 13 is connected to the special optical fiber 14, the timing control trigger 10 is connected to the controller 9, and the controller 9 is connected to the gas cylinder 15 and the laser 1 signal; the special optical fiber 14 is composed of a main optical fiber and multiple branch optical fibers, the main optical fiber is used to transmit laser, the branch optical fibers are used to transmit plasma luminescence, and the branch optical fibers are tightly arranged around the main optical fiber on the end face with a diameter of 2 mm.

[0038] like Figure 2 As shown, the air tube-fiber coupling system 200 includes an air inlet pipe interface 18, a special fiber interface 19, an air outlet pipe 20 and an air outlet pipe interface 21, and the air inlet pipe interface 18, the special fiber interface 19 and the air outlet pipe interface 21 are sealed respectively; the air tube-fiber coupling system 200 is used to couple the special fiber 14 into the air outlet pipe 20, and output it through the air outlet pipe interface 21 and connect it to the air tube 17 fiber coupling interface.

[0039] like Figure 3 As shown, the underwater LIBS probe 300 includes an air pipe 17 fiber coupling interface, a gas buffer chamber 26, a check valve 24, a focusing lens group 25, and a front opening 27; the two ends of the gas buffer chamber 26 are respectively connected to the air pipe 17 fiber coupling interface and the front opening 27, the check valve 24 is arranged between the gas buffer chamber 26 and the front opening 27, and the focusing lens group 25 is used to focus the laser fed from the special optical fiber 14 to the front opening 27 and generate plasma.

[0040] The laser 1 is used to emit laser, the fine-adjustable focal length lens is used to control the laser coupling efficiency, and the fiber coupler 7 is used to feed the laser emitted by the laser 1 into a flexible optical fiber to form a special optical fiber 14. One end of the special optical fiber 14 is connected to the special optical fiber interface 19, and the other end of the air tube 17 is connected to the air tube 17 interface.

[0041] The main part of the fiber LIBS is installed on the shore away from the water environment. The laser is emitted by the laser 1. After being attenuated by the polarizer 2 and the attenuator 3, it is sampled by the spectroscope 5 to the photodiode 4 for monitoring the laser timing. The laser body enters the first flexible optical fiber 8 through the fine-tunable focusing lens 6 and the fiber coupler 7 to obtain the special optical fiber 14; the flexible optical fiber is a multi-mode optical fiber with a high-temperature resistant polyimide coating, with a core diameter of 1000 microns, a numerical aperture of 0.37, a wavelength range of 185-1100nm, and a maximum power density of 40kW / cm2. It can work for a long time in an environment of -190 to 350°C and is suitable for underwater environments. The gas used to form a micro-atmosphere underwater is stored in the gas cylinder 15, and the gas pipe 17 and the special optical fiber 14 are coupled through the gas pipe-fiber coupling system 200 and enter the underwater LIBS probe 300. The plasma light is emitted from the fiber LIBS probe along the reversible optical path into the small optical fiber surrounding the main optical fiber in the special optical fiber 14, and is coaxially transmitted back to the 200-micron second flexible optical fiber 13 and enters the spectrometer 11. The timing of the system is controlled by the controller 9 and the timing control trigger 10.

[0042] The present invention provides a typical nanosecond laser 11 that meets the requirements of underwater environment detection operations, the model is Nd:YAG nanosecond laser 1, the laser 1 operates at a working frequency of 1-10Hz (1064nm), the pulse width FWHM is 10ns, the maximum pulse energy is 35mJ, and the laser beam diameter is 6mm.

[0043] Figure 2 The structure diagram of the air tube-fiber coupling system 200 of the fiber LIBS detection device. A solid metal cylinder is set at the special fiber interface 19. After the special fiber 14 is installed in the groove of the air tube-fiber coupling system 200, the special fiber 14 is sealed by winding a dense rope around it and tightening screws on the upper part. After the optical fiber enters the air tube-fiber coupling system 200, it finally enters the air outlet pipe 20 to complete the waterproof protection of the optical fiber.

[0044] Figure 3 The structure diagram of the underwater LIBS probe 300 of the optical fiber LIBS detection device; the air pipe 17 and the special optical fiber 14 output by the air pipe-optical fiber coupling system 200 are respectively connected and fixed to the air pipe 17 interface and the coupling optical fiber interface 23. The laser is emitted from the special optical fiber 14, collimated and focused on the front opening 27 through the focusing lens group 25 to complete the excitation of the plasma. The gas is input from the gas outlet pipe 20 into the outer gas buffer chamber 26 of the probe, and enters the front opening 27 through the check valve 24 to complete the maintenance of the gas micro-atmosphere at the front end of the probe.

[0045] The specific workflow of the present invention is as follows:

[0046] Figure 4The following is a flowchart of the underwater environment detection operation of the fiber LIBS detection device. First, the fiber LIBS underwater environment detection system is installed, and the air pipe-fiber coupling system 200 and the underwater LIBS probe 300 are connected to check whether the laser is normally output to the front end of the probe and the gas can be output to the front end of the probe without leakage. The underwater robot carries the underwater LIBS probe 300 to the position of the object to be tested. When it reaches the detection surface of the object to be tested, the underwater LIBS probe 300 is adjusted to the front plane of the underwater LIBS probe 300 to vertically fit the surface of the object to be tested, and then the system parameters are set, including the laser frequency and the detection delay of the spectrometer 11, and then the gas valve is opened to control the gas blowing and form a micro-atmosphere underwater. The camera of the underwater robot is used to monitor whether the plasma excitation is good. If it is good, repeat the target measurement. If it is not good, the angle and position of the probe need to be readjusted; repeat the measurement of multiple areas, including analyzing the type and content information of the elements until all the areas to be tested are completed, and the measurement results are recorded in the computer to complete the underwater environment detection.

[0047] Figure 5 The spectrum of 316L stainless steel is detected in the underwater environment of the fiber LIBS system, and a clear and good spectrum is obtained.

[0048] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A fiber-optic laser induced breakdown spectroscopy system for underwater environment detection, characterized in that: include: Optical fiber LIBS main system (100), air tube-optical fiber coupling system (200) and underwater LIBS probe (300); The optical fiber LIBS main system (100) comprises a laser emission component and a gas delivery component; the laser emission component comprises a laser (1), a fine-adjustable focal length lens, an optical fiber coupler (7) and a first flexible optical fiber (8) connected in sequence; the gas delivery component comprises a gas cylinder (15) and an air pipe (17) connected to the gas cylinder (15), and a gas control valve (16) is provided at the opening of the gas cylinder (15); the air pipe-optical fiber coupling system (200) comprises an air inlet pipe interface (18), a special optical fiber interface (19), an air outlet pipe (20) and an air outlet pipe interface (21); the underwater LIBS probe (300) comprises an air pipe interface (22), a coupling optical fiber interface (23), a focusing lens group (25), and a front end opening (27); The laser (1) is used to emit laser light, the finely adjustable focal length lens is used to control laser coupling efficiency, the optical fiber coupler (7) is used to feed the laser light emitted by the laser (1) into a flexible optical fiber to form a special optical fiber (14), one end of the special optical fiber (14) is connected to a special optical fiber interface (19), and the other end of the air pipe (17) is connected to an air intake pipe interface (18); The air pipe-fiber coupling system (200) is used to couple the special optical fiber (14) into the air outlet pipe (20), and output it through the air outlet pipe interface (21), and is respectively connected to the air pipe interface (22) and the coupling optical fiber interface (23); The focusing lens group (25) is used to focus the laser light fed from the special optical fiber (14) to the front end opening (27) and generate plasma.

2. The fiber-optic laser induced breakdown spectroscopy system for underwater environment detection according to claim 1 is characterized in that: The laser (1) and the fine-adjustable focal length lens further include a polarizer (2), an attenuator (3) and a beam splitter (5) connected in sequence, a photodiode (4) is connected below the beam splitter (5), and the laser light is sampled by the beam splitter (5) and converted into an electrical signal by the photodiode (4).

3. The fiber-optic laser induced breakdown spectroscopy system for underwater environment detection according to claim 1 is characterized in that: The laser coupling efficiency is controlled by adjusting the relative position between the finely adjustable focus lens and the first flexible optical fiber (8).

4. The fiber-optic laser induced breakdown spectroscopy system for underwater environment detection according to claim 1 is characterized in that: The optical fiber LIBS main system (100) further comprises a plasma luminescence transmission component, wherein the plasma luminescence transmission component comprises a spectrometer (11), a plasma luminescence transmission optical fiber (12), a second flexible optical fiber (13), a timing control trigger (10) and a controller (9); the spectrometer (11) is connected to the plasma luminescence transmission optical fiber (12) and the timing control trigger (10), respectively, the plasma luminescence transmission optical fiber (12) is connected to the second flexible optical fiber (13), the second flexible optical fiber (13) is connected to the special optical fiber (14), and the timing control trigger (10) is connected to the controller (9).

5. The fiber-optic laser induced breakdown spectroscopy system for underwater environment detection according to claim 1 is characterized in that: The special optical fiber interface (19) is sealed with filler.

6. The fiber-optic laser induced breakdown spectroscopy system for underwater environment detection according to claim 1, characterized in that: The special optical fiber (14) consists of a main optical fiber and a plurality of branch optical fibers, the main optical fiber is used to transmit laser light, the branch optical fibers are used to transmit plasma light emission, and the branch optical fibers surround the main optical fiber and are closely arranged on an end face with a diameter of 2 mm.

7. The fiber-optic laser induced breakdown spectroscopy system for underwater environment detection according to claim 1, characterized in that: The underwater LIBS probe (300) further comprises a gas buffer chamber (26), and two ends of the gas buffer chamber (26) are respectively connected to the optical fiber coupling interface of the air pipe (17) and the front end opening (27).

8. The fiber-optic laser induced breakdown spectroscopy system for underwater environment detection according to claim 7, characterized in that: The underwater LIBS probe (300) further comprises a check valve (24), wherein the check valve (24) is arranged between the gas buffer chamber (26) and the front end opening (27).

9. The fiber-optic laser induced breakdown spectroscopy system for underwater environment detection according to claim 1, characterized in that: The controller (9) is signal-connected to the gas cylinder (15) and the laser (1).

10. An underwater environment detection method using the system according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step (1), adjusting the laser emission component until the optical fiber feed energy fluctuation is stable; Step (2), mounting the underwater LIBS probe (300) on the underwater robot mechanical arm, and manipulating the underwater robot mechanical arm to reach the foreign body position; Step (3), the controller (9) controls the gas control valve (16) to adjust the flow rate so that a preset gas environment is formed at the front end of the probe; In step (4), the controller (9) outputs a signal to control the laser (1) to emit laser light, which is transmitted to the underwater LIBS probe (300) via the main optical fiber of the special optical fiber (14), and is focused on foreign matter in the gas environment by the focusing lens group (25) to generate plasma. The plasma light is transmitted back to the spectrometer (11) by the branch optical fiber of the special optical fiber (14), and the controller (9) outputs a signal to control the spectrometer (11) to collect the plasma light to obtain a spectrum.

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