CN115165850A - Laser-induced breakdown spectroscopy remote detection method - Google Patents
Laser-induced breakdown spectroscopy remote detection method Download PDFInfo
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- CN115165850A CN115165850A CN202210695907.9A CN202210695907A CN115165850A CN 115165850 A CN115165850 A CN 115165850A CN 202210695907 A CN202210695907 A CN 202210695907A CN 115165850 A CN115165850 A CN 115165850A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
- G01N21/73—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited using plasma burners or torches
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
- G02B7/18—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors
- G02B7/182—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors for mirrors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2201/00—Features of devices classified in G01N21/00
- G01N2201/06—Illumination; Optics
- G01N2201/061—Sources
- G01N2201/06113—Coherent sources; lasers
Abstract
The invention discloses a laser-induced breakdown spectroscopy remote detection method, which comprises a laser range finder, and a multi-secondary-mirror self-focusing remote detection device with a laser, a beam expanding lens group, a first laser mirror, a dichroic mirror, a main mirror and a multi-secondary-mirror zooming structure which are sequentially arranged along the propagation direction of a laser beam. The self-focusing detection device used in the detection method has higher zooming precision and can be applied to the analysis and measurement of the composition of the object to be detected in extreme environments which are inconvenient to directly contact in a short distance.
Description
Technical Field
The invention belongs to the technical field of spectral measurement, and relates to a laser-induced breakdown spectroscopy remote detection method.
Background
Laser-Induced Breakdown Spectroscopy (LIBS), also known as Laser-Induced Plasma Spectroscopy (LIPS) or Laser Spark Spectroscopy (LSS), is an element detection technique developed in recent years that belongs to atomic emission Spectroscopy. The LIBS is based on the principle that high-energy pulse laser light is focused on the surface of an object to be detected to ablate the object to generate plasma, in the process of cooling and expanding the laser-induced plasma, a characteristic spectrum of the object to be detected can be obtained through a focusing system and a spectrometer system, and after data processing is carried out, the content of constituent elements of the object to be detected can be obtained.
In recent years, with the rapid development of LIBS technology, important research results have been obtained in the fields of medical treatment, industrial production, deep sea and space exploration, nuclear environment and explosive element detection, and the like.
The most remarkable characteristic of the LIBS is that sample preparation is not needed, and the LIBS is convenient to operate in practical application; the LIBS has little influence on the measured object due to the fact that the working medium of the LIBS is pulse laser, and the LIBS is close to nondestructive detection; and because the optical signal emitted by the laser-induced plasma is strong enough, it provides the possibility for the feasibility of a remote LIBS.
In actual use, the area of a measured object is large, the distance between the measured object and the detection device is not fixed, and the common laboratory fixed focus LIBS cannot meet the requirement. Moreover, the common laboratory LIBS is manual zooming, so that the zooming speed is low, the difficulty in debugging the light path is high, and the requirement on equipment users is high; some LIBS focusing systems and condensing systems are designed into separate structures, so that the size is relatively large, the space utilization rate is low, integration is not easy, and the workload of equipment users is increased.
When an object is detected by the laser-induced breakdown spectroscopy in the prior art, most of the objects are detected in a short distance, and a plurality of scenes which cannot be directly detected in the short distance exist in reality. For example, in high temperature, high radiation hazardous environments, cliffs, deep space ocean. The application requirements of remote LIBS are enormous.
Disclosure of Invention
The invention aims to provide a laser-induced breakdown spectroscopy remote detection method capable of carrying out remote detection.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a laser-induced breakdown spectroscopy remote detection method specifically comprises the following steps:
1) Taking a self-focusing detection device, wherein the self-focusing detection device comprises a laser range finder, and a laser, a beam expanding lens group, a first laser mirror, a dichroic mirror, a main mirror and a multi-auxiliary-mirror zooming structure which are sequentially arranged along the propagation direction of a laser beam; the first laser mirror and the dichroic mirror are arranged in parallel up and down, included angles between the first laser mirror and the dichroic mirror and a horizontal plane are both 45 degrees, and a focusing system is arranged on one side of the dichroic mirror, which is far away from the main mirror, and is connected with a spectrometer; the laser, the multi-lens zooming structure, the laser range finder and the spectrometer are all connected with the computer;
the main mirror adopts a concave spherical reflector with a circular hole in the center, and the concave spherical surface of the main mirror faces to the multi-pair mirror zooming structure;
the multi-lens zooming structure comprises a guide rail and a grating ruler which are arranged in parallel, a grating ruler sliding block which can reciprocate along the length direction of the grating ruler is arranged on the grating ruler, and the grating ruler sliding block is connected with the guide rail through a first connecting support rod; a plurality of rotating arms capable of rotating around the axis of the guide rail in a reciprocating manner are sequentially arranged on the guide rail along the axis direction of the guide rail, the rotating arms adopt electromagnetic clutches, limiting rods and rotating arm supporting rods are fixedly connected onto the rotating arms, secondary mirrors are arranged on the rotating arm supporting rods, the secondary mirrors are convex spherical lenses, the convex surfaces of all the secondary mirrors face the primary mirror, and the curvature radiuses of all the secondary mirrors are different; a first motor and a second motor are respectively installed at two ends of the guide rail, control modules are installed on the first motor and the second motor, and all the control modules are in signal connection with a computer; a second connecting support rod is fixedly connected to a guide rail between the first motor and the rotating arm adjacent to the first motor, the second connecting support rod is positioned below the guide rail, a second laser reflector with the inclination direction opposite to that of the first laser reflector is mounted at the lower end of the second connecting support rod, and the included angle between the second laser reflector and the horizontal plane is 45 degrees;
all the rotating arms are connected with a computer through a control circuit; limit switches with the same number as the rotating arms are arranged on the grating ruler; the first motor adopts a linear motor;
the beam expanding lens group comprises a first biconcave lens and a plano-convex lens which are arranged side by side, and the convex surface of the plano-convex lens is arranged away from the first biconcave lens; the first biconcave lens is adjacent to the laser;
the focusing system comprises a second biconcave lens, a first biconvex lens, a second biconvex lens and a negative meniscus lens which are arranged in sequence side by side, wherein the concave surface of the negative meniscus lens faces the second biconvex lens; the negative meniscus lens is adjacent to the spectrometer;
placing an object to be measured at a pre-designed position, and then starting a computer and a laser range finder; at the moment, all the rotating arms are not electrified;
2) Sending a working instruction to the laser range finder through the computer, wherein the laser range finder sends a laser beam A, and the laser beam A is emitted to the multi-pair zoom structure, reflected by a second laser reflector in the multi-pair zoom structure and emitted to an object to be measured; the surface of an object to be detected is reflected to form a beam of signal light A, the signal light A is transmitted to a second laser reflector and is reflected to a laser range finder through the second laser reflector, the laser range finder receives the returned signal light A, then the distance from a main mirror to the object to be detected is obtained through calculation, the calculation result is sent to a computer, the computer calculates corresponding working parameters, and the working parameters are the distance and the direction of determining which auxiliary mirror is selected to work and the movement of a guide rail;
3) The computer sends out an instruction to start a second motor, the second motor drives the guide rail to rotate, the guide rail drives the driving rotors in all the rotating arms to rotate, meanwhile, the computer energizes the selected rotating arm through the control circuit according to working parameters, the driving rotors and the driven rotors in the energized rotating arms are combined, the driving rotors drive the driven rotors to rotate, the driven rotors drive the limiting rods and the rotating arm supporting rods on the driven rotors to rotate around the horizontal shaft, after the limiting rods and the rotating arm supporting rods rotate 180 degrees, the limiting rods are contacted with a limiting switch on the grating ruler, the limiting switch sends out a signal, the computer sends out an instruction to close the second motor, the selected rotating arm is still in an energized state, at the moment, the secondary mirror fixedly connected to the rotating arm is coaxial with the primary mirror, and the secondary mirror becomes a working secondary mirror; then, the computer sends out an instruction, a first motor is started, the first motor drives the guide rail to drive the working auxiliary mirror to displace towards the direction determined by the computer along the axis direction of the guide rail, the grating ruler continuously measures the position of the working auxiliary mirror in the displacement process, after the working auxiliary mirror meets the displacement distance, the computer judges whether fine zooming is finished or not by reading the data of the grating ruler, if the fine zooming is judged to be finished, the computer closes the first motor, and the displacement of the working auxiliary mirror is finished;
4) The computer starts a laser, the laser emits a pulse laser beam, and the pulse laser beam sequentially passes through a first biconcave lens and a plano-convex lens to amplify laser spots; the amplified laser facula sequentially passes through the first laser reflector and the dichroic mirror, is emitted onto the working secondary mirror through the central circular hole of the primary mirror, is scattered by the convex surface of the working secondary mirror, is reflected onto the concave surface of the primary mirror, is reflected by the concave surface of the primary mirror, and is converged to reach an object to be measured; exciting plasma on the surface of the object to be detected under the condition that the energy density of the converged laser reaches the material threshold of the object to be detected, and emitting signal light B outwards by the plasma in the cooling and expanding process;
5) The signal light B is converged to the working secondary mirror by the concave surface of the primary mirror, reflected by the working secondary mirror and then emitted to the dichroic mirror through the central circular hole of the primary mirror, a part of the signal light B penetrates through the dichroic mirror and then sequentially passes through the second biconcave lens, the first biconvex lens, the second biconvex lens and the negative meniscus lens to enter a spectrometer, the spectrometer is combined with a computer to analyze the received part of the signal light B, and the computer measures the material composition and the content of the object to be measured through a LIBS quantitative analysis algorithm.
The detection method of the invention has the following advantages:
1) And (4) measuring at a long distance. The zoom range of the focusing device used in the detection method is 1-20 meters, the applicability is strong, the method can be used for most field remote measurement operations, the field real-time online detection is realized, the time is saved, and the detection efficiency is improved; the problem of in the actual measuring, the article that awaits measuring is unset with detection device distance is solved. Meanwhile, the focusing device adopts the optical-mechanical-electrical integration technology to realize automatic zooming. And the system error caused by manually adjusting the lens is avoided during zooming, and the measurement precision and efficiency are improved.
2) The zoom precision of the focusing device used in the detection method is higher. Using a multi-pair (each having a different radius of curvature) zoom configuration improves the zoom curve compared to single curvature pair zooming. Zooming with a single curvature secondary mirror, whose zoom curve is very smooth at the end (i.e. the zoom distance varies greatly over a short distance of movement of the secondary mirror); the working auxiliary lenses with different curvatures have different zooming ranges, and ideal parts in the zooming curves of the auxiliary lenses with different curvatures are selected to form a new continuous zooming curve. Namely, the multi-auxiliary-lens zooming structure increases the change of the distance between the main lens and the working auxiliary lens in the Y direction in the same zooming range, so that the zooming is more stable and more accurate in actual operation. Meanwhile, the precision requirement of a mechanical system is reduced, and the cost is saved. And moreover, the structure is compact, and the integration is easy. The collecting system and the focusing system are coaxial, the utilization rate of the lens is high, and the structures of all parts are tightly connected, so that the space utilization rate is high, namely the structure is small, and the lens is convenient to be integrated with other devices for use.
3) The method can be applied to the analysis and measurement of the composition of the object to be measured in extreme environments which are inconvenient to directly contact in close range, such as: in industrial metallurgy, short-distance component measurement of molten metal is difficult to realize due to overhigh temperature; or element measurement is carried out in the strong magnetic radiation environment of a nuclear power station and the like; or elemental measurements in an explosive environment, etc. The self-focusing device can also be carried on some automatic mechanical devices (unmanned aerial vehicles, unmanned vehicles, cloud platforms and the like) to realize long-term automatic detection of the object to be detected, such as: and carrying on an unmanned aerial vehicle to carry out long-term automatic real-time online detection on the element component content of the sample to be detected.
Drawings
Fig. 1 is a schematic view of a self-focusing detection apparatus employed in the detection method of the present invention.
Fig. 2 is a schematic diagram of a zoom structure of a plurality of pairs of mirrors in the autofocus detection apparatus of fig. 1.
FIG. 3 is a schematic diagram of a beam expanding lens set in the self-focusing detection apparatus shown in FIG. 1.
Fig. 4 is a schematic diagram of a focusing system in the autofocus detection device of fig. 1.
Fig. 5 is a state diagram of the use of the zoom structure of the plurality of pairs of mirrors in the autofocus detecting apparatus shown in fig. 1.
FIG. 6 is a graph comparing single pair zooming and multi-pair zooming.
In the figure: 1. the system comprises a computer, 2, a laser, 3, a beam expanding lens group, 4, a first laser reflector, 5, a primary mirror, 6, a multi-secondary-mirror zooming structure, 7, an object to be measured, 8, a distance measuring system, 9, a dichroic mirror, 10, a focusing system, 11, a spectrometer, 12, a secondary mirror, 13, a second laser reflector, 14, a guide rail, 15, a grating ruler, 16, a first connecting supporting rod, 17, a limiting rod, 18, a grating ruler sliding block, 19, a first motor, 20, a second connecting supporting rod, 21, a rotating arm supporting rod, 22, a rotating arm, 23, a second motor, 24, a working secondary mirror, 25, a first biconcave lens, 26, a plano-convex lens, 27, a second biconcave lens, 28, a first biconvex lens, 29, a second biconvex lens and 30, a negative meniscus lens.
Detailed Description
The invention is further explained below with reference to the drawings and the detailed description.
The invention provides a method for remotely detecting an article 7 to be detected by laser-induced breakdown spectroscopy, which comprises the following steps:
1) Taking the self-focusing detection device shown in fig. 1, the self-focusing detection device comprises a laser range finder 8, and a laser 2, a beam expanding lens group 3, a first laser mirror 4, a dichroic mirror 9, a main mirror 5 and a multi-auxiliary-mirror zooming structure 6 which are sequentially arranged along the propagation direction of a laser beam; the first laser reflector 4 and the dichroic mirror 9 are arranged in parallel up and down, included angles between the first laser reflector 4 and the dichroic mirror 9 and a horizontal plane are both 45 degrees, a focusing system 10 is arranged on one side of the dichroic mirror 9, which is far away from the main mirror 5, and the focusing system 10 is connected with a spectrometer 11; the laser 2, the multi-lens zooming structure 6, the laser range finder 8 and the spectrometer 11 are all connected with the computer 1.
The main mirror 5 adopts a concave spherical reflector with a round hole with the diameter of 4mm at the center, and the concave spherical surface of the main mirror 5 faces the multi-pair mirror zooming structure 6.
As shown in fig. 2, the multi-lens zoom structure 6 in the self-focusing detection device comprises a guide rail 14 and a grating scale 15 which are arranged in parallel, wherein a grating scale slider 18 which can reciprocate along the length direction of the grating scale 15 is installed on the grating scale 15, and the grating scale slider 18 is connected with the guide rail 14 through a first connecting support rod 16; a plurality of rotating arms 22 capable of rotating around the axis of the guide rail 14 in a reciprocating manner are sequentially arranged on the guide rail 14 along the axis direction of the guide rail 14, a limiting rod 17 and a rotating arm supporting rod 21 are fixedly connected onto the rotating arms 22, one end of the limiting rod 17 is fixedly connected with the rotating arms 22, the other end of the limiting rod 17 is a free end, the lower end of the rotating arm supporting rod 21 is fixedly connected with the rotating arms 22, the upper end of the rotating arm supporting rod 21 is provided with a secondary mirror 12, the secondary mirrors 12 are convex spherical lenses, the convex surfaces of all the secondary mirrors 12 face the primary mirror 5, and the curvature radiuses of all the secondary mirrors 12 are different; a first motor 19 and a second motor 23 are respectively installed at two ends of the guide rail 14, control modules are installed on the first motor 19 and the second motor 23, and all the control modules are in signal connection with the computer 1; the second motor 23 is connected to the guide rail 14 by spline coupling. A second connecting support rod 20 is fixedly connected to the guide rail 14 between the first motor 19 and the rotating arm 22 adjacent to the first motor 19, the second connecting support rod 20 is positioned below the guide rail 14, the upper end of the second connecting support rod 20 is fixedly connected with the guide rail 14, a second laser reflector 13 is installed at the lower end of the second connecting support rod 20, the included angle between the second laser reflector 13 and the horizontal plane is 45 degrees, and the inclination direction of the second laser reflector 13 is opposite to that of the first laser reflector 4.
The rotary arm 22 is an electromagnetic clutch, preferably a DC24V electromagnetic clutch (a mini high torque clutch of Sinfonia, japan). A limiting rod 17 and a rotating arm supporting rod 21 are fixedly connected to the outer wall of a driven rotor of the electromagnetic clutch, and an included angle between the limiting rod 17 and the rotating arm supporting rod 21 is 90 degrees; the driving rotor of the electromagnetic clutch is fitted around the guide rail 14.
All the rotating arms 22 are connected to the computer 1 via a control circuit.
The grating ruler 15 is provided with limit switches with the same number as the rotating arms 22.
The first motor 19 is a linear motor.
All the swivel arms 22 are located between the first connecting strut 16 and the second connecting strut 20.
The length of the internal spline in the spline coupling is different from the length of the external spline. The external spline is installed on the guide rail 14, the internal spline is installed on the motor shaft of the second motor 23, and a gap is formed between the end surface of the external spline facing the second motor 23 and the end surface of the motor shaft of the second motor 23 extending into the internal spline.
As shown in fig. 3, the beam expanding lens group 3 in the self-focusing detection apparatus includes a first biconcave lens 25 and a plano-convex lens 26 arranged side by side, and a convex surface of the plano-convex lens 26 is arranged away from the first biconcave lens 25. A first biconcave lens 25 is adjacent the laser 2 and a plano-convex lens 26 is adjacent the first laser mirror 4.
As shown in fig. 4, the focusing system 10 in the self-focusing detection apparatus includes a second biconcave lens 27, a first biconvex lens 28, a second biconvex lens 29 and a negative meniscus lens 30, which are arranged side by side in sequence, wherein the concave surface of the negative meniscus lens 30 faces the second biconvex lens 29; a negative meniscus lens 30 is adjacent the spectrometer 11 and a second biconcave lens 27 is adjacent the dichroic mirror 9.
When the machine is not in operation, all the limiting rods 17 are arranged along the positive direction of the X axis, all the rotating arm supporting rods 21 are arranged along the positive direction of the Z axis, and the guide rails 14 are arranged along the direction of the Y axis;
placing an object to be detected 7 at a pre-designed position, then starting the computer 1 and the laser range finder 8, and at the moment, not electrifying all the rotating arms 22;
2) Obtaining a zooming parameter: a working instruction is sent to the laser range finder 8 through the computer 1, the laser range finder 8 sends a laser beam A, and the laser beam A irradiates to the multi-pair zoom structure 6, is reflected by a second laser reflector 13 in the multi-pair zoom structure 6 and irradiates to an object 7 to be measured; the surface of the object 7 to be measured reflects a beam of signal light A, the signal light A shoots at the second laser reflector 13 and is reflected to the laser range finder 8 through the second laser reflector 13, the laser range finder 8 receives the returned signal light A and then calculates to obtain the distance from the main mirror 5 to the object 7 to be measured (the actual distance measured by the range finder 8 is the distance from the range finder 8 to the second reflector 13 and the distance from the second reflector 13 to the object 7 to be measured, and because the working secondary mirror 24 returns to the original position after each measurement, the distance between the main mirror 5 and the second reflector 13 is determined, only the actual distance measured by the range finder 8 is required to subtract the distance from the range finder 8 to the second reflector 13, and the distance from the main mirror 5 to the second reflector 13 is required to obtain the distance from the main mirror 5 to the object 7 to be measured), and the calculation result is sent to the computer 1, the computer 1 calculates corresponding working parameters, namely determines which secondary mirror 12 is selected to work and the moving distance and moving direction of the guide rail 14;
3) The computer 1 sends out an instruction to start a second motor 23, the second motor 23 drives the guide rail 14 to rotate through spline connection, the guide rail 14 drives driving rotors in all the rotating arms 22 to rotate, meanwhile, the computer 1 powers on the selected rotating arm 22 through a control circuit according to the obtained working parameters, the driving rotor and the driven rotor in the powered rotating arm 22 are combined, the driving rotor drives the driven rotor to rotate, the driven rotor drives a limiting rod 17 and a rotating arm supporting rod 21 on the driving rotor to rotate around a horizontal shaft, after the limiting rod 17 and the rotating arm supporting rod 21 rotate 180 degrees, the limiting rod 17 is in contact with a limiting switch on a grating ruler 15, the limiting switch sends out a signal, the computer 1 sends out an instruction to close the second motor 23, the selected rotating arm 22 is still in a powered state, at the moment, an auxiliary mirror 12 fixedly connected to the rotating arm 22 is coaxial with the main mirror 5, the auxiliary mirror 12 becomes a working auxiliary mirror 24, and coarse zooming is completed, as shown in fig. 5; then, the computer 1 sends out an instruction, the first motor 19 is started, the first motor 19 drives the guide rail 14 to drive the working auxiliary mirror 24 to displace along the axial direction of the guide rail 14 to the direction determined by the computer 1, in the displacement process, the grating ruler 15 continuously measures the position of the working auxiliary mirror 24, after the working auxiliary mirror 24 meets the displacement distance, the computer 1 judges whether the fine zooming is finished or not by reading the data of the grating ruler 15, if the fine zooming is judged to be finished, the computer 1 closes the first motor 19, and the displacement of the working auxiliary mirror 24 is finished;
4) The computer 1 starts the laser 2, the laser 2 emits a pulse laser beam, and the pulse laser beam sequentially passes through the first biconcave lens 25 and the plano-convex lens 26 to enlarge the laser spot by 2.5 times; the amplified laser facula sequentially passes through the first laser reflector 4 and the dichroic mirror 9, then is emitted onto the working secondary mirror 24 through a central circular hole of the primary mirror 5, is diverged and reflected onto the concave surface of the primary mirror 5 by the convex surface of the working secondary mirror 24, is reflected by the concave surface of the primary mirror 5, and is converged to reach the object 7 to be measured; when the energy density of the converged laser reaches the material threshold of the object 7 to be detected, plasma can be excited on the surface of the object 7 to be detected, and the plasma emits signal light B outwards in the cooling and expanding process
5) The signal light B is converged to the working secondary mirror 24 by the concave surface of the primary mirror 5, reflected by the working secondary mirror 24 and then emitted to the dichroic mirror 9 through the central circular hole of the primary mirror 5, a part of the signal light B passes through the dichroic mirror 9 and then sequentially passes through the second biconcave lens 27, the first biconvex lens 28, the second biconvex lens 29 and the negative meniscus lens 30 to enter the spectrometer 11, the spectrometer 11 is combined with the computer 1 to analyze a part of the received signal light B, and the computer 1 measures the material composition and the content of the object 7 to be measured through a LIBS (laser induced breakdown spectroscopy) quantitative analysis algorithm.
After the measurement is completed, the computer 1 starts the first motor 19 to drive the guide rail 14 to move reversely, so that the rotating arm 22 returns to the original position before the linear movement, then the computer 1 starts the second motor 23 to drive the guide rail 14 to rotate reversely, so that the selected rotating arm rotates reversely by 180 degrees, the auxiliary working mirror 24 returns to the original position, then the computer 1 sends out an electric signal, the control circuit cuts off the power of the selected rotating arm 22, and the rotating arm 22 returns to the separated state.
The signal light B may be visible light having a wavelength of 200nm to 800nm, which is a part of light that can pass through the dichroic mirror 9. The visible light band in the signal light B is transmitted through the dichroic mirror 9 and emitted to the focusing system 10, which eliminates the interference of the pulse laser to the spectrometer 11.
The visible light transmitted by the dichroic mirror 9 is converged to an optical fiber connected with a spectrometer 11 by a focusing system 10; the spectrometer 11 generates spectral data according to the collected signal light, and finally obtains the composition of the object 7 to be measured through software analysis.
The focusing system 10, the primary mirror 5 and the working secondary mirror 24 are coaxial; the working secondary mirror 24 and the primary mirror 5 form a cassegrain system.
During the detection process, since the first motor 19 is small, when the second motor 23 drives the guide rail 14 to rotate, the first motor 19 rotates together with the guide rail 14. When the first motor 19 works, the second motor 23 stops working, the first motor 19 drives the guide rail 14 to move linearly, the inner spline and the outer spline cannot be separated in the moving process due to the fact that the length of the inner spline and the length of the outer spline in spline connection are different, and the linear moving distance of the guide rail 14 is not large, and the moving distance of the guide rail 14 can be guaranteed enough by the gap between the end face of the outer spline and the end face of the motor shaft of the second motor 23.
As shown in fig. 5, the distance D between the main mirror 5 and the working sub-mirror 24 is:
D=d1+d2+d3+(n－1)Δd（1）
(1) In the formula, d1 is a zero point of the grating ruler 15, that is, a distance between an end surface of the grating ruler 15 facing the primary mirror 5 and a plane of the primary mirror 5 in the Y direction;
d2 is the relative distance between the zero point of the grating ruler 15 (the end surface of the grating ruler 15 facing the end of the main mirror 5) and the end of the grating ruler slide block 18 facing the zero point of the grating ruler 15 in the Y direction, and is also the reading of the grating ruler;
d3 is the distance between one end of the grating ruler slide block 18 facing the zero point of the grating ruler 15 and the axis of the rotating arm support rod 21 of the secondary mirror 12 adjacent to the grating ruler slide block 18 in the Y direction;
Δ d is the distance between the axes of the rotating arm struts 21 where the adjacent two sub mirrors 12 are located in the Y direction;
n is the number of the rotating sub-mirrors 12 sorted among all the sub-mirrors (sorted in order from the main mirror 5 to the first motor 19 direction, the number of the sub-mirror 12 closest to the main mirror 5 is 1, and so on).
The self-focusing detection device adopted by the detection method of the invention performs coarse zooming through the selected auxiliary mirror 12, namely, the value of n in the formula (1) is changed by selecting different auxiliary mirrors 12. In the fine zoom in the detection method, the computer 1 sends an instruction to a motor module of the first motor 19, and the first motor 19 drives the guide rail 14 to move linearly, namely, the value of d2 in the formula (1) is changed.
The working auxiliary mirror 24 of the self-focusing detection device adopted in the remote detection method of the invention diverges the light beam, the main mirror 5 converges the light beam, and the distance D in the Y direction between the main mirror 5 and the working auxiliary mirror 24 can be changed to zoom: after obtaining the zooming parameters, the second motor 23 selects a suitable sub-mirror 12 from the plurality of sub-mirrors 12 to perform coarse zooming, and the first motor 19 drives the guide rail 14 to drive the working sub-mirror 24 to move to perform fine zooming.
The first biconcave lens 25 and the plano-convex lens 26 are arranged in parallel and are both vertical to the propagation direction of light, and the beam expanding lens group 3 of the device can expand the light by 2.5 times.
The first biconvex lens 28 and the second biconcave lens 27 are used to eliminate aberrations. A second biconvex lens 29 and a negative meniscus lens 30 are used to focus the light beam.
Under the condition that the laser 2 emits a light spot with the radius of 4mm, the diameter of the focused light spot is smaller than 1mm, so that the laser energy can be gathered in a small enough space range, and the laser can excite high-temperature and high-density plasma on the surface of an object 7 to be detected.
The focusing light path (the first biconcave lens 25 and the planoconvex lens 26) and the collecting light path (the second biconcave lens 27, the first biconvex lens 28, the second biconvex lens 29 and the negative meniscus lens 30) are coaxially arranged, the optimization of focusing and collecting at different distances can be controlled by using the least adjustment amount, the diameter of a focusing light spot of the collected light coupled into the optical fiber is smaller than 0.6mm after the collected light passes through the coaxial collecting system, and the telescopic focusing collecting system can be used for ensuring that the spectral signals of a wide range of wave bands can be focused into the core diameter of the optical fiber at different distances.
The self-focusing device of the invention uses a plurality of auxiliary lenses 12 to select zooming, the resolution of a zooming curve of the self-focusing device is improved, namely the same focusing distance variation, and the variation of the distance between the main lens 5 and the working auxiliary lens 24 corresponding to the multi-lens zooming system is larger than the variation of the distance between the main lens and the working auxiliary lens of a single-lens zooming system in the Y direction in the prior art, so that the zooming error can be reduced, and the measurement result is more accurate.
The curve of the multi-pair zoom of the self-focusing apparatus of the present invention is compared with that of the single-pair zoom of the prior art, as shown in fig. 6, in which the abscissa is the focusing distance and the ordinate is the distance between the main mirror 5 and the working sub-mirror 24 in the Y direction. As can be seen from the figure, the resolution of the multi-lens zoom curve is greater than that of the single-lens zoom curve, that is, the same focus distance variation, and the distance variation between the main lens 5 and the working sub-lens 24 in the Y direction corresponding to the multi-lens zoom system is greater than that between the main lens 5 and the working sub-lens 24 in the Y direction of the single-lens zoom system, which can reduce the error of zooming and make the measurement result more accurate.
The self-focusing device in the invention is a coaxial remote LIBS automatic zooming device using multi-lens zooming. The entire apparatus is controlled by the computer 1.
Claims (5)
1. A laser-induced breakdown spectroscopy remote detection method is characterized by comprising the following steps:
1) taking a self-focusing detection device, wherein the self-focusing detection device comprises a laser range finder (8), and a laser (2), a beam expanding lens group (3), a first laser reflector (4), a dichroic mirror (9), a main mirror (5) and a multi-auxiliary-mirror zooming structure (6) which are sequentially arranged along the propagation direction of a laser beam; the first laser reflector (4) and the dichroic mirror (9) are arranged in parallel up and down, included angles between the first laser reflector (4) and the dichroic mirror (9) and a horizontal plane are both 45 degrees, a focusing system (10) is arranged on one side, away from the main mirror (5), of the dichroic mirror (9), and the focusing system (10) is connected with the spectrometer (11); the laser (2), the multi-pair lens zooming structure (6), the laser range finder (8) and the spectrometer (11) are all connected with the computer (1);
the main mirror (5) adopts a concave spherical reflector with a circular hole in the center, and the concave spherical surface of the main mirror (5) faces the multi-pair mirror zooming structure (6);
the multi-auxiliary-lens zooming structure (6) comprises a guide rail (14) and a grating ruler (15) which are arranged in parallel, a grating ruler sliding block (18) which can reciprocate along the length direction of the grating ruler (15) is arranged on the grating ruler (15), and the grating ruler sliding block (18) is connected with the guide rail (14) through a first connecting support rod (16); a plurality of rotating arms (22) capable of rotating around the axis of the guide rail (14) in a reciprocating manner are sequentially installed on the guide rail (14) along the axis direction of the guide rail (14), the rotating arms (22) adopt electromagnetic clutches, limiting rods (17) and rotating arm supporting rods (21) are fixedly connected to the rotating arms (22), secondary mirrors (12) are installed on the rotating arm supporting rods (21), the secondary mirrors (12) are convex spherical lenses, the convex surfaces of all the secondary mirrors (12) face the primary mirror (5), and the curvature radiuses of all the secondary mirrors (12) are different; a first motor (19) and a second motor (23) are respectively installed at two ends of the guide rail (14), control modules are installed on the first motor (19) and the second motor (23), and all the control modules are in signal connection with the computer (1); a second connecting support rod (20) is fixedly connected to the guide rail (14) between the first motor (19) and the rotating arm (22) adjacent to the first motor (19), the second connecting support rod (20) is positioned below the guide rail (14), a second laser reflector (13) with the inclination direction opposite to that of the first laser reflector (4) is mounted at the lower end of the second connecting support rod (20), and the included angle between the second laser reflector (13) and the horizontal plane is 45 degrees;
all the rotating arms (22) are connected with the computer (1) through a control circuit; limit switches with the same number as that of the rotating arms (22) are arranged on the grating ruler (15); the first motor (19) adopts a linear motor;
the beam expanding lens group (3) comprises a first biconcave lens (25) and a plano-convex lens (26) which are arranged side by side, and the convex surface of the plano-convex lens (26) is arranged away from the first biconcave lens (25); the first biconcave lens (25) is adjacent to the laser (2);
the focusing system (10) comprises a second biconcave lens (27), a first biconvex lens (28), a second biconvex lens (29) and a negative meniscus lens (30) which are arranged side by side in sequence, wherein the concave surface of the negative meniscus lens (30) faces to the second biconvex lens (29); the negative meniscus lens (30) is adjacent to the spectrometer (11);
placing an object to be measured (7) at a pre-designed position, and then starting a computer (1) and a laser range finder (8); at the moment, all the rotating arms (22) are not electrified;
2) A working instruction is sent to the laser range finder (8) through the computer (1), the laser range finder (8) sends a laser beam A, and the laser beam A irradiates to the multi-pair zoom structure (6), is reflected by a second laser reflector (13) in the multi-pair zoom structure (6) and irradiates to an object to be measured (7); the surface of an object to be detected (7) is reflected to form a signal light A, the signal light A irradiates to a second laser reflector (13) and is reflected to a laser range finder (8) through the second laser reflector (13), the laser range finder (8) receives the returned signal light A and then calculates to obtain the distance from a main mirror (5) to the object to be detected (7), the calculation result is sent to a computer (1), the computer (1) calculates corresponding working parameters, and the working parameters are the distance and the direction for determining which auxiliary mirror (12) is selected to work and the guide rail (14) moves;
3) The computer (1) sends an instruction to start a second motor (23), the second motor (23) drives the guide rail (14) to rotate, the guide rail (14) drives driving rotors in all rotating arms (22) to rotate, meanwhile, the computer (1) energizes the selected rotating arm (22) through a control circuit according to working parameters, the driving rotor and a driven rotor in the energized rotating arm (22) are combined, the driving rotor drives the driven rotor to rotate, the driven rotor drives a limiting rod (17) and a rotating arm supporting rod (21) on the driven rotor to rotate around a horizontal shaft, when the limiting rod (17) and the rotating arm supporting rod (21) rotate for 180 degrees, the limiting rod (17) is in contact with a limiting switch on a grating ruler (15), the limiting switch sends a signal, the computer (1) sends an instruction to turn off the second motor (23), the selected rotating arm (22) is still in an energized state, at this time, an auxiliary mirror (12) fixedly connected on the rotating arm (22) is coaxial with the main mirror (5), and the auxiliary mirror (12) becomes a working auxiliary mirror (24); then, the computer (1) sends an instruction, a first motor (19) is started, the first motor (19) drives the guide rail (14) to drive the working auxiliary mirror (24) to move towards the direction determined by the computer (1) along the axis direction of the guide rail (14), the grating ruler (15) continuously measures the position of the working auxiliary mirror (24) in the moving process, after the working auxiliary mirror (24) meets the moving distance, the computer (1) judges whether fine zooming is finished or not by reading the data of the grating ruler (15), if the fine zooming is judged to be finished, the computer (1) closes the first motor (19), and the movement of the working auxiliary mirror (24) is finished;
4) The computer (1) starts the laser (2), the laser (2) emits a pulse laser beam, and the pulse laser beam sequentially passes through the first biconcave lens (25) and the plano-convex lens (26) to amplify laser spots; amplified laser spots sequentially pass through the first laser reflector (4) and the dichroic mirror (9), are shot onto the working secondary mirror (24) through a central circular hole of the primary mirror (5), are scattered and reflected onto the concave surface of the primary mirror (5) by the convex surface of the working secondary mirror (24), are reflected by the concave surface of the primary mirror (5), and are converged to reach an object to be measured (7); exciting plasma on the surface of the object (7) to be detected under the condition that the energy density of the converged laser reaches the material threshold of the object (7) to be detected, and emitting signal light B outwards by the plasma in the cooling and expanding process;
5) The signal light B is converged to the working auxiliary mirror (24) by the concave surface of the main mirror (5), reflected by the working auxiliary mirror (24) and then emitted to the dichroic mirror (9) through the central circular hole of the main mirror (5), a part of the signal light B passes through the dichroic mirror (9) and then sequentially passes through the second biconcave lens (27), the first biconvex lens (28), the second biconvex lens (29) and the negative meniscus lens (30) to enter the spectrometer (11), the spectrometer (11) is combined with the computer (1) to analyze a part of the received signal light B, and the computer (1) measures the material components and the content of the object to be measured (7) through a LIBS quantitative analysis algorithm.
2. The laser-induced breakdown spectroscopy remote detection method of claim 1, wherein after the measurement is completed, the computer (1) starts the first motor (19) to drive the guide rail (14) to move in reverse to return the rotary arm (22) to the original position before the linear movement, then the computer (1) starts the second motor (23) to drive the guide rail (14) to rotate in reverse to rotate the selected rotary arm in reverse 180 °, the working auxiliary mirror (24) returns to the original position, and then the computer (1) sends an electric signal, the control circuit powers off the selected rotary arm (22), and the rotary arm (22) returns to the separated state.
3. The method for remote detection of laser-induced breakdown spectroscopy according to claim 2, wherein a part of the signal light B transmitted through the dichroic mirror (9) is visible light having a wavelength of 200nm to 800 nm.
4. The laser-induced breakdown spectroscopy remote detection method according to claim 1, wherein a limit rod (17) and a rotating arm support rod (21) are fixedly connected to an outer wall of a driven rotor of the electromagnetic clutch, and an included angle between the limit rod (17) and the rotating arm support rod (21) is 90 degrees; the driving rotor of the electromagnetic clutch is sleeved on the guide rail (14).
5. The laser induced breakdown spectroscopy remote detection method of claim 1, wherein the second motor (23) is connected to the guide rail (14) by spline coupling; the length of the internal spline and the length of the external spline in the spline coupling are different.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115839943A (en) * | 2023-02-13 | 2023-03-24 | 合肥金星智控科技股份有限公司 | Laser-induced spectroscopy system, spectrum calibration method and electronic equipment |
| CN117147526A (en) * | 2023-10-31 | 2023-12-01 | 西北师范大学 | Large-area soil pH value rapid detection method |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115839943A (en) * | 2023-02-13 | 2023-03-24 | 合肥金星智控科技股份有限公司 | Laser-induced spectroscopy system, spectrum calibration method and electronic equipment |
| CN117147526A (en) * | 2023-10-31 | 2023-12-01 | 西北师范大学 | Large-area soil pH value rapid detection method |
| CN117147526B (en) * | 2023-10-31 | 2024-02-06 | 西北师范大学 | Large-area soil pH value rapid detection method |
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