CN109444111B - Optical fiber LIBS detection system and method capable of selecting double-pulse mode - Google Patents

Abstract

The application relates to the technical field of laser diagnosis, in particular to an optical fiber LIBS detection system and method capable of selecting a double-pulse mode, wherein the system comprises an integrated optical fiber laser, an optical fiber LIBS probe, a control detection module and an optical fiber transmission module; the system obtains the plasma emission spectrum signals with different degrees of double-pulse enhancement through the method, the output laser time sequence of the main pulse laser and the auxiliary pulse laser can be changed by changing the position of the light shielding plate and adjusting the position of the auxiliary probe on the guide rail to switch the four double-pulse fiber LIBS detection modes, so that the sample to be detected can be detected in multiple directions, and obvious characteristic spectral lines can be obtained, so that the element types and the content of the sample to be detected can be accurately analyzed. The method has the advantages of reducing the influence of matrix effect on detection, along with high repeatability, high spectral signal-to-noise ratio, high analysis speed, safe and reliable measurement process, high element detection limit and capability of remote online monitoring.

Description

Optical fiber LIBS detection system and method capable of selecting double-pulse mode

Technical Field

The application relates to the technical field of laser diagnosis, in particular to an optical fiber LIBS detection system and method capable of selecting a double-pulse mode.

Background

LIBS is a short term for Laser-Induced Breakdown Spectroscopy (Laser-Induced Breakdown Spectroscopy), and this technique focuses on the surface of a sample to form plasma, and analyzes the emission spectrum of the plasma by using a spectrometer to identify the elemental composition in the sample, so as to identify, classify, characterize and quantitatively analyze the material. Since the LIBS technology appeared, the technology was recognized as a new technology with a wide prospect, and will bring numerous innovative applications to the analysis field. LIBS is used as a new material identification and quantitative analysis technology, can be used in laboratories, and can also be used in on-line detection of industrial fields. The main characteristics are as follows: rapid direct analysis, almost no need for sample preparation; almost all elements can be detected; multiple elements can be analyzed simultaneously; matrix morphology diversity-almost all solid state samples can be detected. The LIBS makes up the defects of the traditional element analysis method, has obvious advantages particularly in the application fields of material analysis, plating layer/thin film analysis, defect detection, jewelry identification, forensic evidence identification, powder material analysis, alloy analysis and the like in a micro area, and can be widely applied to different fields of geology, coal, metallurgy, pharmacy, environment, scientific research and the like. In addition to traditional laboratory applications, LIBS is still a few elemental analysis technologies that can be made into handheld portable devices, and is considered to be the only elemental analysis technology that can be made online up to now. This will greatly expand the analytical technology from the laboratory field to outdoor, on-site, and even production processes.

In the prior art, the principle of the double-pulse laser induced breakdown spectroscopy is that a first beam of pulse laser carries out pre-ablation and optimized excitation environment on a sample, and a second beam of pulse laser carries out secondary induced excitation on the sample, so that a plasma emission spectrum signal with higher intensity is obtained. Measuring different areas of a measured sample by using a double-pulse laser breakdown spectrum measuring system to obtain spectra, and transmitting the collected spectra to a computer by using a spectrometer; software on the computer analyzes and compares the acquired spectral data with LIBS element spectral information in an NIST database to obtain the element types and corresponding spectral line information contained in the sample to be detected, and finally obtains the detection results of the element types and the element contents contained in the sample to be detected by analyzing the characteristic spectral lines and the intensities of the related elements.

However, the detection of the apparatus and method for analyzing the double-pulse laser breakdown spectrum has a deviation, mainly because the stability of the laser pulse is poor during the detection, the detector generates noise, and the signal is damaged in the transmission process, the ablation process is not repeatable, the safety in use is low, and the influence of the environment can be caused, so that the finally obtained characteristic spectral line is not obviously difficult to perform quantitative analysis on the characteristic spectral line. With the increasing expansion of the application range of laser-induced breakdown spectroscopy, the conventional double-pulse laser-induced breakdown spectroscopy technology cannot meet the current needs.

Disclosure of Invention

The application provides an optical fiber LIBS detection system and method capable of selecting a double-pulse mode, and aims to solve the problems that a traditional optical fiber LIBS is easily influenced by a sample matrix effect, and has the defects and problems that laser pulse stability is poor, repeatability is poor, an ablation process is not repeatable, a detector generates noise interference, a detection limit is high, a non-metal element characteristic spectral line is not obvious and quantitative analysis is difficult, and the like.

A first aspect of the present application provides a selectable double pulse mode fiber LIBS detection system, the system comprising: a selectable double-pulse mode fiber LIBS detection system, the system comprising: an integrated optical fiber device, an optical fiber LIBS probe, a control detection module and an optical fiber transmission module,

the programmable pulse delay generator in the control detection module is respectively and electrically connected with the control end of the first nanosecond laser and the control end of the second nanosecond laser in the integrated optical fiber device;

a computer in the control detection module is respectively and electrically connected with a monitoring end of a first laser energy meter, a monitoring end of a second laser energy meter and a signal control end of a light shielding plate in the integrated optical fiber device;

an oscilloscope in the control detection module is respectively and electrically connected with a monitoring end of a first photoelectric detector and a monitoring end of a second photoelectric detector in the integrated optical fiber device;

the main probe in the fiber LIBS probe is respectively connected with the main pulse laser output end of the integrated fiber device and the spectrometer in the control detection module through a first transmission fiber and a third transmission fiber in the fiber transmission module, and the auxiliary probe in the fiber LIBS probe is connected with the auxiliary pulse laser output end of the integrated fiber device through a second transmission fiber in the fiber transmission module.

Optionally, the center of the main pulse laser output end of the integrated optical fiber device and the centers of the first optical fiber adapter, the third plano-convex lens, the fourth plano-convex lens and the dichroic mirror in the optical fiber LIBS probe are on the same straight line.

Optionally, the center of the secondary pulse laser output end of the integrated optical fiber device and the centers of the third optical fiber adapter, the seventh plano-convex lens and the eighth plano-convex lens in the optical fiber LIBS probe are on the same straight line.

Optionally, the center of the output end of the third transmission fiber is collinear with the centers of the second fiber adapter, the fifth plano-convex lens, the sixth plano-convex lens and the reflector in the fiber LIBS probe, and antireflection films are plated on the surfaces of the fifth plano-convex lens and the sixth plano-convex lens.

Optionally, the positions of the photoelectric switch transmitting end and the photoelectric switch receiving end in the optical fiber LIBS probe are set at the same height of the bracket.

Optionally, the main probe is fixedly connected with the guide rail, and the auxiliary probe is slidably connected with the guide rail.

Optionally, an included angle between optical axes of the laser output by the main probe and the auxiliary probe ranges from 45 degrees to 90 degrees.

Optionally, the detection modes that the system can provide include a collinear double-pulse LIBS mode, a crossed double-pulse LIBS mode, a reheating orthogonal double-pulse LIBS mode, and a pre-ablation orthogonal double-pulse LIBS mode.

A second aspect of the present application provides a method for fiber LIBS detection in a selectable double-pulse mode, the method being applied to the system according to any one of claims 1 to 8, wherein the method includes:

s1, opening a movable door in the fiber LIBS probe, placing the sample to be tested on an object carrying lifting table in the fiber LIBS probe, and closing the movable door;

s2, lifting the object carrying lifting table to drive the sample to be detected to slowly rise until the upper surface of the sample to be detected shields a light beam emitted by a photoelectric switch emission end in the optical fiber LIBS probe, and stopping rising;

s3, opening the indicating light of a first nanosecond laser and a second nanosecond laser in the integrated optical fiber device, and adjusting the position of the sample to be detected on the object lifting table to enable the area to be detected on the sample to be detected to fall on the midpoint position of the light focusing spots of the indicating light of the first nanosecond laser (11) and the second nanosecond laser;

s4, adjusting the emitting laser parameters of the first nanosecond laser, the ICCD (35) gate width signal delay and the position of the object lifting table;

s5, observing the signal-to-back ratio of the characteristic radiation spectrum and the ordinate of the spectrogram, if the signal-to-back ratio is high and the ordinate of the spectrogram has the maximum value, performing the step S6, if the signal-to-back ratio is low, returning to the step S4, and performing the step S6 until the characteristic radiation spectrum with the high signal-to-back ratio and the ordinate of the spectrogram has the maximum value is observed;

s6, switching four double-pulse fiber LIBS modes and setting double-pulse targeting accumulation times;

s7, sampling background light by using a spectrometer in the control detection module to obtain the accumulated spectrum information of the sample to be detected;

s8, comparing the spectrum data in the database to obtain characteristic spectral lines corresponding to the element types in the sample to be detected;

s9, further performing a double-pulse fiber LIBS experiment on the standard sample, and quantitatively detecting the element content in the sample to be detected through an LIBS element calibration curve;

and S10, lowering the object lifting platform to the bottommost part.

Optionally, the control precision of the object lifting table is 10 μm.

The technical scheme provided by the application comprises the following beneficial technical effects:

the application provides a multimode fiber LIBS detection system with selectable double-pulse mode, which comprises: the system is applied to set the time delay between a main pulse and a secondary pulse through a programmable pulse delay generator according to actual requirements and set the time delay of an ICCD collected spectrum, an oscilloscope is used for observing whether the time delay of each path of signal is accurate or not, and a spectrometer collects the spectrum and performs light splitting treatment on the spectrum after the ICCD starts to work; setting the accumulation times of double-pulse target shooting in the software of a computer; the spectrometer samples the environmental background spectrum before each target shooting; after the double-pulse fiber laser targeting is finished, the spectrometer accumulatively transmits the collected multiple spectra to the computer; the software on the computer analyzes and compares the acquired spectral data with LIBS element spectral information in an NIST database to obtain the element types and corresponding spectral line information contained in the sample to be detected, and can further perform a double-pulse fiber laser targeting experiment of a standard sample. The method has the advantages of reducing the influence of matrix effect on detection, along with high repeatability, high spectral signal-to-noise ratio, high analysis speed, safe and reliable measurement process, high element detection limit and capability of remote online monitoring. The method solves the problems that the traditional optical fiber LIBS is easily influenced by the matrix effect of a sample, and has the defects of poor laser pulse stability, poor repeatability, unrepeatable ablation process, noise interference generated by a detector, high detection limit, unobvious non-metal element characteristic spectral line, difficulty in quantitative analysis and the like.

Drawings

In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without any creative effort.

Fig. 1 is a schematic structural diagram of an optical fiber LIBS detection system with a selectable double pulse mode according to an embodiment of the present disclosure.

Fig. 2 is a schematic structural diagram of an optical fiber LIBS probe provided in an embodiment of the present application.

Fig. 3 is a flow chart illustrating switching of four double-pulse fiber LIBS detection modes according to an embodiment of the present disclosure.

Fig. 4 is a comparison graph of the collinear double-pulse fiber LIBS enhanced spectrum and the single-pulse fiber LIBS spectrum provided in the embodiments of the present application.

Fig. 5 is a flowchart of an optical fiber LIBS detection method in an optional double-pulse mode according to an embodiment of the present disclosure.

Description of reference numerals:

11. a first nanosecond laser; 12. a first photodetector; 13. a first beam splitter; 14. a second spectroscope; 15. a first laser energy meter; 16. a third beam splitter; 17. a first reflective mirror; 18. a first plano-convex lens; 19. a second nanosecond laser; 110. a second photodetector; 111. a second laser energy meter; 112. a fourth spectroscope; 113. a fifth spectroscope; 114. a sixth beam splitter; 115. a second reflective mirror; 116. a second plano-convex lens; 117. a visor; 21. a support; 22. a main probe; 23. a guide rail; 24. a secondary probe; 25. an object lifting table; 26. a photoelectric switch transmitting terminal; 27. a movable door; 28. a photoelectric switch receiving end; 221. a first fiber optic adapter; 222. a second fiber optic adapter; 223. a first sleeve; 224. a third plano-convex lens; 225. a fourth plano-convex lens; 226. a dichroic mirror; 227. a fifth plano-convex lens; 228. a sixth plano-convex lens; 229. a mirror; 241. a third fiber optic adapter; 242. a seventh plano-convex lens; 243. an eighth plano-convex lens; 244. a second sleeve; 31. a computer; 32. an oscilloscope; 33. a programmable pulse delay generator; 34. a spectrometer; 35. ICCD; 41. a first transmission optical fiber; 42. a second transmission optical fiber; 43. a third transmission fiber.

Detailed Description

The application provides an optical fiber LIBS detection system and method capable of selecting a double-pulse mode, and aims to solve the problems that a traditional optical fiber LIBS is easily influenced by a sample matrix effect, and has the defects and problems that laser pulse stability is poor, repeatability is poor, an ablation process is not repeatable, a detector generates noise interference, a detection limit is high, a non-metal element characteristic spectral line is not obvious and quantitative analysis is difficult, and the like.

Illustratively, as shown in fig. 1, the system for fiber LIBS detection in an optional double-pulse mode provided in the first aspect of the present application includes: the device comprises an integrated optical fiber device, an optical fiber LIBS probe, a control detection module and an optical fiber transmission module.

The integrated optical fiber device comprises a mainboard, and a first nanosecond laser, a first spectroscope, a first photoelectric detector, a second spectroscope, a first laser energy meter, a third spectroscope, a first reflector, a first plano-convex lens, a second nanosecond laser, a fourth spectroscope, a second photoelectric detector, a fifth spectroscope, a second laser energy meter, a sixth spectroscope, a second reflector, a second plano-convex lens and a light shielding plate which are arranged on the mainboard.

The integrated fiber laser is provided with 9 interfaces which are respectively a first nanosecond laser output end, a second nanosecond laser output end, a light shielding plate signal control end, a control end of a first nanosecond laser, a first photoelectric detector monitoring end, a first laser energy meter monitoring end, a control end of a second nanosecond laser, a second photoelectric detector monitoring end and a second laser energy meter monitoring end; the first nanosecond laser and the second nanosecond laser are respectively and correspondingly arranged on the first side of the mainboard, the first photoelectric detector and the first laser energy meter are arranged on the second side of the mainboard, and the second photoelectric detector, the second laser energy meter, the light shielding plate, the first plano-convex lens and the second plano-convex lens are arranged on the third side of the mainboard.

The first spectroscope, the second spectroscope, the third spectroscope, the first reflector and the first plano-convex lens are arranged on a laser light path output by the first nanosecond laser, the positions of the first spectroscope and the third spectroscope correspond to the positions of the first photoelectric detector and the first laser energy meter respectively, the second spectroscope is arranged between the first spectroscope and the third spectroscope, and the third spectroscope is arranged between the first reflector and the second spectroscope.

The fourth spectroscope, the fifth spectroscope, the sixth spectroscope, the second reflector and the second plano-convex lens are arranged on a laser light path output by the second nanosecond laser, the positions of the fourth spectroscope and the fifth spectroscope correspond to the positions of the second photoelectric detector and the second laser energy meter respectively, and the sixth spectroscope is arranged between the fifth spectroscope and the second reflector.

The light shielding plate is arranged on a main board of the integrated laser, and the position of the light shielding plate can be controlled by a computer and is arranged between the second spectroscope and the sixth spectroscope or between the sixth spectroscope and the second reflector.

The first nanosecond laser and the second nanosecond laser are both devices capable of emitting nanosecond laser, laser emitted by the first nanosecond laser and the second nanosecond laser is focused to break down a sample to be detected, a ray characteristic spectral line of the sample to be detected can be obtained by collecting a plasma luminescence spectrum, and the element type and the content of each element in the sample to be detected are analyzed and obtained according to the obtained spectral line. In the application, a first nanosecond laser is used as a transmitting end of main pulse laser, a second nanosecond laser is used as a transmitting end of secondary pulse, the output laser energy of the first nanosecond laser and the output laser energy of the second nanosecond laser can be adjusted according to actual requirements, the time sequence and the time interval between the main pulse laser and the secondary pulse laser are set through a programmable pulse delay generator, plasma emission spectrum signals with different degrees of double-pulse enhancement can be obtained, the enhancement effect of the obtained plasma emission spectrum signals is stronger through setting the time sequence and the time interval of laser pulses of the two lasers, the observed characteristic spectral line is more obvious, and the result of qualitatively and quantitatively analyzing the element content through an algorithm is more accurate.

The beam splitter is an optical device capable of splitting a beam into multiple beams, one path of laser output by a first nanosecond laser penetrates through a first beam splitter, the other path of laser is split into the first photoelectric detector by the first beam splitter, the second beam splitter receives the light penetrating through the first beam splitter and then continuously penetrates through a third beam splitter, the third beam splitter divides the laser into two paths, one path of laser penetrates through the third beam splitter and reaches a first reflector, the other path of laser is split into a first laser energy meter, and the first reflector reflects the laser and focuses the laser into a first transmission optical fiber through a first plano-convex lens.

One path of laser output by the second nanosecond laser penetrates through the fourth spectroscope, one path of laser is split into a second photoelectric detector by the fourth spectroscope, the fifth spectroscope receives the light penetrating through the fourth spectroscope and divides the laser into two paths, one path of laser penetrates through the sixth spectroscope and reaches the second reflecting mirror, one path of laser is split into a second laser energy meter, and the second reflecting mirror reflects the laser and focuses the laser into a second transmission optical fiber through the second plano-convex lens.

The beam splitter and the output laser optical axis of the nanosecond laser form an included angle of 45 degrees, so that the beam splitter can divide the laser beam received by the nanosecond laser into two paths, wherein the beam divided into the photoelectric detector and the laser energy meter is just vertical to the laser beam output by the nanosecond laser.

A photodetector is a device that converts an optical signal into an electrical signal, and the principle of the photodetector is that the electrical conductivity of the irradiated material changes due to radiation, and the radiation signal collected by the photodetector carries the following information: light intensity distribution, temperature distribution, spectral energy distribution, radiation flux and the like, and the radiation signals can be analyzed, recorded, stored and displayed after being processed by an electronic circuit.

One path of laser output by the first nanosecond laser penetrates through the first spectroscope, and the other path of laser is split into a first photoelectric detector by the first spectroscope, wherein the first photoelectric detector is connected with the oscilloscope and used for monitoring the time sequence of a main pulse laser output signal.

One path of laser output by the second nanosecond laser penetrates through the fourth spectroscope, and the other path of laser is split by the fourth spectroscope into a second photoelectric detector, wherein the second photoelectric detector is connected with the oscilloscope and used for monitoring the time sequence of the output signal of the secondary pulse laser.

The laser energy meter is characterized in that a detector, an amplifier electrically connected with the detector and a signal output unit are sequentially arranged in a tubular metal shell, a ceramic hollow cavity is arranged between a laser incidence port of the shell and the detector, the ceramic hollow cavity is a closed hollow cylinder, and the axial direction of the cylinder is parallel to the direction of laser entering the shell. Common energy detection methods are classified into a photothermal method and a radio-electric method. The photo-thermal method uses thermopile or heat release point material as an absorption detector during sensing, i.e. the laser and the absorber are pollinated, and then the temperature rise of the absorber is tested by a thermoelectric sensor, so that the heat value of the absorber, i.e. the laser energy value, is obtained. The photoelectric method uses a photoelectric detector or a semiconductor photodiode as a photoelectric detector of a sensing device, after an optical signal is converted into an electric signal, the electric signal is processed by a charge integrator to obtain a voltage signal which is in direct proportion to the input light pulse energy, and thus the energy measurement is completed. Because the dynamic range of the photodiode is large, the measurement speed is high, the envelope change of signals can be reflected, and the price is low, so the photoelectric method is selected to complete the measurement of the laser energy emitted by the first nanosecond laser and the second nanosecond laser.

One path of laser output by the first nanosecond laser penetrates through the first spectroscope, one path of laser is split into the first photoelectric detector by the first spectroscope, the second spectroscope receives light penetrating through the first spectroscope and then continues to penetrate through the third spectroscope, the third spectroscope divides the laser into two paths, one path of laser penetrates through the third spectroscope and reaches the first reflector, one path of laser is split into the first laser energy meter, the first laser energy meter is connected with a computer, the ratio of the laser energy entering the first energy laser meter to the laser energy output by the first nanosecond laser is measured in advance through experiments, and a corresponding splitting coefficient is set in the computer, so that the actual energy of the laser output by the first nanosecond laser can be monitored.

The laser output by the second nanosecond laser penetrates through the fourth spectroscope, one laser output by the second nanosecond laser penetrates through the fourth spectroscope, the other laser output by the fourth spectroscope is split into the second photoelectric detector by the fourth spectroscope, the fifth spectroscope receives the light penetrating through the fourth spectroscope and divides the laser into two paths, the other laser output by the sixth spectroscope reaches the second reflecting mirror, the other laser output by the second photoelectric detector is split into a second laser energy meter, the second laser energy meter is connected with a computer, the ratio of the laser energy entering the second energy laser meter to the laser energy output by the second nanosecond laser is measured in advance through experiments, and a corresponding splitting coefficient is set in the computer, so that the actual energy of the laser output by the second nanosecond laser can be monitored.

A mirror is a mirror that is used specifically to reflect light, either to make it parallel or to increase the brightness of one side of the mirror. After the first reflector reflects part of laser emitted by the first nanosecond device, the laser is focused into the first transmission optical fiber through the first plano-convex lens; and after the second reflector reflects part of the laser of the second nanosecond laser, the part of the laser is focused into the second transmission optical fiber through the second plano-convex lens. Because the laser facula that first nanosecond laser instrument and second nanosecond laser instrument transmitted is circular, in order to obtain better focus effect, facula quality and fiber coupling effect, so this application sets up the center of first speculum, the center of first plano-convex lens, the center setting of first transmission optic fibre input and on the collinear and the center of second speculum, the center of second plano-convex lens, the center setting of second transmission optic fibre input are on the collinear.

The reflector is arranged at a position forming an included angle of 45 degrees with the optical axis of the laser output by the nanosecond laser, and the reflector is used for changing the optical path of the laser output by the nanosecond laser, so that the optical axis of the laser can penetrate through the plano-convex lens and be focused into the transmission optical fiber.

The focusing focus of the laser optical axis is arranged at a position 2-3mm away from the input end of the optical fiber, and the purpose of the arrangement is to prevent the optical fiber from being damaged due to overhigh laser energy focused into the plano-convex lens.

The light shielding plate is used for shielding the light beam and preventing the light beam from passing through a certain section of light path, and the position of the light shielding plate can be controlled by a computer in the application and is arranged between the second spectroscope and the sixth spectroscope or between the sixth spectroscope and the second reflector; for example, as shown in fig. 1, the position of the light shielding plate may be from an a position to a b position, or from the b position to the a position, in this application, a double-pulse LIBS detection mode in which a main pulse and a secondary pulse are matched with each other is used to analyze the type of elements contained in the sample to be detected and the content of each element, in this application, the output optical path of the secondary pulse output by the second nanosecond laser is adjusted by changing the position of the light shielding plate. For example, as shown in fig. 3, which is a flow chart of switching between four double-pulse fiber LIBS detection modes provided by the present application, when the light shielding plate is placed at position b, the detection mode is a collinear double-pulse LIBS mode; the light shielding plate is arranged at the position of a, and the detection mode is a non-collinear double-pulse LIBS mode.

Optionally, the first nanosecond laser selected for use in the present application is Nd: YAG nanosecond laser, output laser wavelength is 1064nm, frequency is 1-10Hz, pulse width FWHM is 10ns, maximum pulse energy is 150mJ, laser beam diameter is 6mm, the second nanosecond laser is Nd: YAG nanosecond laser, wavelength is 1064nm, operating frequency is 1-20 Hz, pulse width is 10ns, pulse energy is adjustable for 0-120 mJ, and different types of nanosecond laser can be replaced according to actual needs according to different use scenes.

Exemplarily, as shown in fig. 2, the structure diagram of the optical fiber LIBS probe is a quarter-circle structure with a hollow interior, and includes a bracket, a main probe, a guide rail, an auxiliary probe, an object lifting platform, a photoelectric switch transmitting end, a movable door and a photoelectric switch receiving end, where the main probe is fixedly connected with the guide rail, the auxiliary probe is slidably connected with the guide rail, the movable door is fixed on an outer wall of a first side of the bracket through a bolt, the object lifting platform is installed inside the movable door, the photoelectric switch transmitting end and the photoelectric switch receiving end are disposed at the same height inside the movable door, and a light-emitting optical axis of the photoelectric switch transmitting end, the object lifting platform and a surface of a sample to be detected are parallel.

The main probe is used for receiving laser of the first nanosecond laser, is fixedly connected with the guide rail and is fixed at the position m of the support, the main probe comprises a first optical fiber adapter, a second optical fiber adapter and a first sleeve, the first optical fiber adapter and the second optical fiber adapter are horizontally arranged at the top end of the first sleeve, the inside of the first sleeve is uniformly divided into two parts, the first part comprises a third plano-convex lens, a fourth plano-convex lens and a dichroic mirror, the third plano-convex lens, the fourth plano-convex lens and the dichroic mirror are fixed in the first sleeve through clamping rings, the third plano-convex lens and the fourth plano-convex lens are sequentially and vertically arranged with the side wall of the first sleeve, and the dichroic mirror and the side wall of the first sleeve form an angle of 45; the second part comprises a fifth plano-convex lens, a sixth plano-convex lens, a reflector and a clamping ring, the fifth plano-convex lens and the sixth plano-convex lens are fixed in the first sleeve through the clamping ring, the fifth plano-convex lens and the sixth plano-convex lens are sequentially and vertically arranged with the side wall of the first sleeve, and the reflector and the side wall of the first sleeve are arranged at an angle of 45 degrees and are parallel to the dichroic mirror.

The first optical fiber adapter, the third plano-convex lens, the fourth plano-convex lens and the dichroic mirror are all arranged on the same light path, and the output end of the first output optical fiber, the center of the first optical fiber adapter, the center of the third plano-convex lens, the center of the fourth plano-convex lens and the center of the dichroic mirror are arranged on the same straight line. Divergent laser output by the first transmission optical fiber is changed into parallel light through the third plano-convex lens, and then passes through the fourth plano-convex lens, penetrates through the dichroic mirror and is focused on the surface of a sample to be detected, and plasma plume is generated.

The second optical fiber adapter, the fifth plano-convex lens, the sixth plano-convex lens and the reflector are arranged on the same light path, the center of the input end of the third output optical fiber, the center of the second optical fiber adapter, the center of the fifth plano-convex lens, the center of the sixth plano-convex lens and the center of the reflector are arranged on the same straight line, a plasma plume luminous beam generated after double-pulse laser targeting is reflected by the dichroic mirror and then transmitted to the reflector, and then reflected to the sixth plano-convex lens by the reflector, the plasma plume luminous beam is changed into parallel light by the sixth plano-convex lens and then focused into a third transmission optical fiber by the fifth plano-convex lens, the third transmission optical fiber is connected with the spectrometer, the spectrometer can obtain a LIBS spectrum of the plasma plume, and can qualitatively and quantitatively analyze the types of elements and the content of the elements in a sample to be detected according to characteristic spectral lines.

The dichroic mirror selected for use in the application is a long-wave-pass dichroic mirror, the diameter of the dichroic mirror is 25.4mm, and the cut-off wavelength of the dichroic mirror is 900 nm. Because the reflectance of the dichroic mirror 42 can reach 90% or more for light with a wavelength of 400-872 nm; the light with the wavelength of 932-1300nm can reach the light transmission rate of more than 90 percent.

The diameter of the third plano-convex lens selected by the application is 25.4mm, and the focal length is 35.1 mm; the fourth plano-convex lens has a diameter of 25.4mm and a focal length of 16 mm. Because the laser beam which is converged downwards by the fourth plano-convex lens passes through the dichroic mirror, the refractive index of the medium is changed, and the optical path transmitted during laser focusing is prolonged, so that the distance between the laser beam focusing spot of the main probe and the center of the fourth plano-convex lens is 16mm greater than the focal length of the fourth plano-convex lens.

The diameter of the fifth plano-convex lens selected by the application is 25.4mm, and the focal length is 35 mm; the sixth plano-convex lens has a diameter of 25.4mm and a focal length of 40 mm. Antireflection films are plated on the surfaces of the fifth plano-convex lens and the sixth plano-convex lens, and the range of the enhanced wavelength is between 350 and 700 nm.

The auxiliary probe is used for receiving the laser of the second nanosecond laser and is connected with the guide rail in a sliding mode, an included angle between an optical axis of the laser output by the auxiliary probe and an optical axis of the laser output by the main probe is set to be theta, and the range of the theta is 45-90 degrees. By changing the position of the secondary probe on the guideway, the pulse mode can be classified into a quadrature type double pulse LIBS mode or a cross type double pulse LIBS mode. The auxiliary probe comprises a third optical fiber adapter, a seventh plano-convex lens, an eighth plano-convex lens and a second sleeve, the third optical fiber adapter is arranged at the top end of the second sleeve, and the seventh plano-convex lens and the eighth plano-convex lens are sequentially perpendicular to the side wall of the second sleeve.

The third optical fiber adapter, the seventh plano-convex lens and the eighth plano-convex lens in the auxiliary probe are positioned on the same light path, the center of the output end of the second output optical fiber, the center of the third optical fiber adapter, the center of the seventh plano-concave lens and the center of the eighth plano-concave lens are positioned on the same straight line, divergent laser output from the second transmission optical fiber is changed into parallel light through the seventh plano-convex lens and then is focused on the surface of a sample to be detected through the eighth plano-convex lens, and the position of a focusing light spot and a laser beam focusing light spot passing through the main probe are superposed on the same position of the surface of the sample to be detected.

The diameter of the seventh plano-convex lens selected in the application is 25.4mm, and the focal length is 35.1 mm; the eighth plano-convex lens has a diameter of 25.4mm and a focal length of 30 mm.

The third plano-convex lens and the seventh plano-convex lens with larger focal lengths are selected, so that laser beams output from the output end of the transmission optical fiber have larger-area light spots when being changed into parallel light through the plano-convex lens; and a fourth plano-convex lens and an eighth plano-convex lens with smaller focal length are selected, so that the parallel laser beams can be focused to a focusing spot with a smaller area when being converged by the plano-convex lenses, and the laser targeting effect is enhanced.

The photoelectric switch sensor consists of a photoelectric switch transmitting end and a photoelectric switch receiving end. The light emitting diode in the emitting end of the photoelectric switch continuously emits light signals to the receiving end of the photoelectric switch, and the phototriode in the receiving end of the photoelectric switch converts the received light signals into electric signals to be transmitted to a computer. The photoelectric switch transmitting end and the photoelectric switch receiving end are arranged at the same height, and the light-emitting optical axis of the photoelectric detector is parallel to the object lifting table and the surface of the sample to be detected, so that the laser beam focusing focus passing through the main probe and the laser beam focusing focus passing through the auxiliary probe are coincided and fall in the center of the light-emitting optical axis.

The control detection module comprises a computer, a programmable pulse delay generator, an oscilloscope, a spectrometer and an ICCD, wherein the computer is respectively and electrically connected with the first laser energy meter, the second laser energy meter and the signal control end of the light shielding plate, the programmable pulse delay generator is respectively and electrically connected with the spectrometer, the ICCD, the first nanosecond laser and the second nanosecond laser, and the oscilloscope is respectively and electrically connected with the ICCD, the first photoelectric detector and the second photoelectric detector.

The computer is used for monitoring the light-emitting energy of the two lasers, controlling the position of the light shielding plate, setting the accumulation times of double-pulse targeting, controlling the lifting of the object carrying lifting table, displaying the obtained spectrogram, setting the gate width of the ICCD, automatically controlling the LIBS detection process, automatically comparing a database to obtain an element characteristic spectral line and qualitatively and quantitatively analyzing the element types and content.

The programmable pulse delay generator is used for setting the time delay between a main pulse and a secondary pulse and setting the time delay of an ICCD (integrated circuit compact disc) collected spectrum, the application proposes that double pulses are used for detecting the types and the contents of elements in a sample to be detected, the set time of the main pulse and the set time of the secondary pulse for outputting laser are different, and the purpose of the method is to enhance the signal of a plasma emission spectrum and collect an obvious characteristic spectral line for analysis; on the other hand, the programmable pulse delay generator can also adjust the detection delay of the spectrometer for collecting the plasma luminescence spectrum by setting the delay between the ICCD external trigger signal and the secondary pulse output laser.

The oscilloscope is used for observing a time delay of each path of signals, wherein the oscilloscope observes a signal after the main pulse laser is emitted, the oscilloscope observes a signal after the secondary pulse laser is emitted, the oscilloscope observes a signal when the ICCD starts to collect spectra, and the inherent time delay of equipment and the transmission time delay of the electrical signals also need time, so that even if the programmable pulse delay generator is used for setting the time for the main pulse and the secondary pulse to emit laser in the time for emitting the laser, the oscilloscope is needed for observation so as to be adjusted in the subsequent process in order to observe whether the main pulse and the secondary pulse emit the laser in sequence on the set time difference; the reason for observing the signal when the ICCD works is the same as the observation reason of the emission of the main pulse and the secondary pulse laser. On the other hand, the propagation delay of the laser in the air is ignored, but the propagation time of the laser between the first transmission fiber and the second transmission fiber is several times of the time taken for the laser to propagate the same distance in the air, so that the propagation delay is not negligible for the whole detection process in the microsecond order; the propagation delay of the laser between the first transmission optical fiber and the second transmission optical fiber is measured in advance through an oscilloscope and recorded as t, and finally the delay of the actual ICCD collected spectrum is the delay of an ICCD action signal and a secondary pulse output laser signal displayed on the oscilloscope minus t.

The spectrometer is a device for measuring intensities of spectral lines at different wavelength positions by using a photo-detector such as a photomultiplier tube and the like, can separate polychromatic light into spectra, can be used for splitting plasma luminous light generated after double-pulse focusing and puncturing the surface of a sample to be measured according to wave bands, and displays the plasma self-luminous spectrum of the sample to be measured by combining the photosensitive intensity of an ICCD area array through a computer.

An ICCD (intensified CCD) enhanced charge coupled device is formed by coupling an image enhancer and a visible light CCD, and is used for controlling how long a secondary pulse laser is applied to a sample to be detected, and then a generated spectrum is collected. The door opening action is carried out only after the ICCD receives an external touch control signal, and the light split by the spectrometer can be sensed by the photosensitive area array in the ICCD. The ICCD can set corresponding door width on a computer according to detection requirements, wherein the door width is a time period from the opening to the closing of the ICCD, namely a time period from the sensing of the ICCD by the plasma self-luminescence after the light is split by the spectrometer.

Setting the accumulation times of double-pulse target shooting in the software of a computer; the spectrometer samples the environmental background spectrum before each target shooting; after the double-pulse fiber laser targeting is finished, the spectrometer accumulatively transmits the collected multiple spectra to the computer; software on the computer analyzes and compares the acquired spectral data with LIBS element spectral information in an NIST database to obtain element types and corresponding spectral line information contained in a sample to be detected, a double-pulse fiber laser targeting experiment of a standard sample can be further carried out, and the element content in the sample to be detected is quantitatively detected through an LIBS element calibration curve; after each detection, the object lifting platform is controlled by the computer to descend to the bottommost part again.

The main probe is connected with the main pulse laser output end of the optical fiber transmission module through a first transmission optical fiber, the auxiliary probe is connected with the auxiliary pulse laser output end of the optical fiber transmission module through a second transmission optical fiber, and the main probe is connected with the spectrometer through a third transmission optical fiber. For the input end of the optical fiber, the optical fiber with large numerical aperture is beneficial to the focusing and coupling of laser; at the output end, the small-numerical-aperture optical fiber is beneficial to refocusing and targeting after the output light beam is transmitted, because the divergence and off-axis property of the light beam transmitted in the multimode optical fiber make the output laser light beam difficult to focus and target, and the low-numerical-aperture optical fiber provides lower light beam divergence and uniform spot size.

Optionally, the optical fiber selected by the present application is a silica-clad multimode optical fiber. The lengths of the first transmission optical fiber and the second transmission optical fiber are both 3m, the core diameter of the optical fiber is 800 μm, the numerical aperture is 0.37, and the maximum power density is 1GW/cm 2; the length of the third transmission fiber was 3m, the core diameter of the fiber was 400 μm, and the numerical aperture was 0.22. The first transmission optical fiber, the second transmission optical fiber and the third transmission optical fiber which are made of different cladding materials, have different models, different lengths, different diameters and different numerical apertures can be replaced according to actual needs aiming at different use scenes.

Exemplarily, as shown in fig. 3, a flow chart for selecting four detection modes for a double-pulse fiber LIBS detection system is provided, where the frequency of a first nanosecond laser is set to be 1Hz, and the output laser energy is set to be 40 mJ; the frequency of the second nanosecond laser is 1Hz, and the output laser energy is 35 mJ; the time interval of the laser pulses output by the two lasers is set to be 9 mus, and then the control computer selects to place the light shielding plate at the a position or the b position, namely selects the collinear double-pulse LIBS mode or the noncolinear double-pulse LIBS mode; if the light shielding plate is selected to be placed at the position a, the position of the auxiliary probe on the guide rail can be adjusted, and the auxiliary probe is fixed at the position n at the bottommost end of the guide rail or other positions on the guide rail by using a screw, namely an orthogonal double-pulse LIBS mode or a crossed double-pulse LIBS mode is selected; if the orthogonal double-pulse LIBS mode is selected, the laser pulse time sequence output by the two lasers is changed by setting the parameters of the programmable pulse delay generator; if the output of the main pulse laser is prior to the output of the auxiliary pulse laser, the mode is a reheating orthogonal double-pulse LIBS mode; if the output of the secondary pulse laser is prior to that of the main pulse laser, the pre-etching orthogonal double-pulse LIBS mode is adopted.

1. Common line type double pulse LIBS mode

The collinear structure means that the main pulse laser and the secondary pulse laser pass through the same optical focusing system, focus the laser energy to the same point and penetrate through the surface of the sample through a certain time delay and then vertical incidence. The light shielding plate is positioned at the position b and blocks the light path of the sixth spectroscope, so that no laser beam is focused into the second transmission optical fiber, and the secondary probe does not play a role at the moment. The main pulse laser output from the first nanosecond laser sequentially passes through the first spectroscope, the second spectroscope and the third spectroscope, is reflected by the first reflector, is focused into the first transmission optical fiber through the first plano-convex lens, and is focused onto the surface of a sample to be detected through the main probe; the secondary pulse laser output from the second nanosecond laser sequentially passes through the fourth spectroscope and the fifth spectroscope, then is reflected to the second spectroscope by the sixth spectroscope, the light beam reflected by the second spectroscope is continuously transmitted along the light path of the main pulse laser, and finally is focused into the first transmission optical fiber by the first plano-convex lens and is focused to the same position on the surface of the sample to be measured through the main probe. The output laser energy of the first nanosecond laser and the second nanosecond laser can be adjusted according to requirements, and the time sequence and the time interval between the main pulse laser and the secondary pulse laser are adjusted, so that collinear double-pulse enhanced plasma emission spectrum signals of different degrees are obtained.

2. Interleaved double-pulse LIBS mode

The cross structure is that after the main pulse laser and the secondary pulse laser pass through two different optical focusing systems, two beams of laser form a certain angle to focus and puncture the surface of a sample. The light shielding plate 3 is positioned at the position a and blocks a light path reflected by the sixth beam splitter, and the auxiliary probe is fixed at the other positions on the guide rail, which are not n positions, namely theta is more than 45 degrees and less than or equal to 90 degrees. At the moment, laser output from the second nanosecond laser sequentially passes through the fourth spectroscope, the fifth spectroscope and the sixth spectroscope, is reflected by the second reflector, is focused into the second transmission optical fiber through the second plano-convex lens, and is focused onto the surface of the sample to be detected through the secondary probe; the main pulse laser is still focused to the same position on the surface of the sample to be measured 13 along the output optical path of the first nanosecond laser through the main probe. The output laser energy, time sequence and time delay of the two nanosecond lasers can be adjusted according to requirements, and the value of the theta angle is adjusted, so that crossed double-pulse enhanced plasma emission spectrum signals of different degrees are obtained.

3. Reheat orthogonal type double pulse LIBS mode

The orthogonal structure means that the main pulse laser and the secondary pulse laser are orthogonal to each other, one beam is parallel to the surface of a sample, the other beam is perpendicular to the surface of the sample, and respectively reach and break down the surface of the sample after passing through two different optical focusing systems. Reheating means that laser light perpendicular to the surface of a sample reaches and ablates the sample to excite plasma, and then laser light reaching parallel to the surface of the sample heats the generated plasma. The light shielding plate is located at the position a, the light path reflected by the sixth beam splitter is blocked, the auxiliary probe 34 is fixed at the position n on the guide rail, namely theta is equal to 90 degrees, and the output laser time sequence of the first nanosecond laser is prior to the output laser time sequence of the second nanosecond laser. At the moment, the main pulse laser is vertically focused on the surface of the sample to be measured through the main probe along the output light path of the first nanosecond laser; and the secondary pulse laser is focused at the same position in parallel to the surface of the sample to be detected through the secondary probe along the output light path of the second nanosecond laser. The output laser energy and the time delay of the two nanosecond lasers can be adjusted according to requirements, and therefore reheating orthogonal double-pulse enhanced plasma emission spectrum signals of different degrees are obtained.

4. Pre-ablation orthogonal double-pulse LIBS mode

The pre-etching refers to that laser parallel to the surface of a sample firstly reaches and breaks down air near the surface of the sample to generate plasma, and then the laser which reaches and is vertical to the surface of the sample is focused to ablate the surface of the sample. The light shielding plate 3 is located at the position a, a light path reflected by the sixth beam splitter is blocked, the auxiliary probe is fixed at the position n on the guide rail, namely theta is equal to 90 degrees, and the output laser time sequence of the second nanosecond laser is prior to the output laser time sequence of the first nanosecond laser. The transmission optical paths of the main pulse laser and the auxiliary pulse laser are the same as the reheating orthogonal double-pulse LIBS mode. The output laser energy and the time delay of the two nanosecond lasers can be adjusted according to requirements, so that pre-ablation orthogonal double-pulse enhanced plasma emission spectrum signals of different degrees are obtained.

Illustratively, as shown in fig. 5, a second aspect of the present application provides a flow chart of a method for detecting an optical fiber LIBS in a selectable double-pulse mode, where the method is applied to the above system, and the method includes:

s1, opening a movable door in the fiber LIBS probe, placing the sample to be tested on an object carrying lifting table in the fiber LIBS probe, and closing the movable door;

s2, lifting the object carrying lifting table to drive the sample to be detected to slowly rise until the upper surface of the sample to be detected shields a light beam emitted by a photoelectric switch emission end in the optical fiber LIBS probe, and stopping rising;

s3, opening the indicating light of a first nanosecond laser and a second nanosecond laser in the integrated optical fiber device, adjusting the position of the sample to be detected on the object lifting table, and enabling the area to be detected on the sample to be detected to fall on the midpoint position of the light focusing spot of the indicating light of the first nanosecond laser and the second nanosecond laser;

s4, adjusting the emitting laser parameters of the first nanosecond laser, the ICCD gate width signal delay and the position of the object lifting table;

s5, observing the signal-to-back ratio of the characteristic radiation spectrum and the ordinate of the spectrogram, if the signal-to-back ratio is high and the ordinate of the spectrogram has the maximum value, performing the step S6, if the signal-to-back ratio is low, returning to the step S4, and performing the step S6 until the characteristic radiation spectrum with the high signal-to-back ratio and the ordinate of the spectrogram has the maximum value is observed;

s6, switching four double-pulse fiber LIBS modes and setting double-pulse targeting accumulation times;

s7, sampling background light by using a spectrometer in the control detection module to obtain the accumulated spectrum information of the sample to be detected;

s8, comparing the spectrum data in the database to obtain characteristic spectral lines corresponding to the element types in the sample to be detected;

s9, further performing a double-pulse fiber LIBS experiment on the standard sample, and quantitatively detecting the element content in the sample to be detected through an LIBS element calibration curve;

and S10, lowering the object lifting platform to the bottommost part.

The loading platform is a fine-adjustable electric upgrading platform, and the control precision of the loading platform can reach 10 mu m; the movable door is made of transparent plastic fibers. Before each laser target shooting, the object carrying lifting table is lowered to the bottommost part; opening the movable door, placing the sample to be detected on the object carrying lifting table, and closing the movable door; controlling the lifting of the carrying platform through a computer to drive the sample to be detected to slowly rise; when the upper surface of the sample to be tested shields the light beam emitted by the photoelectric switch transmitting end, the electric signal transmitted outwards by the photoelectric switch collecting end is changed, and at the moment, the computer controls the object carrying lifting table to stop acting; turning on the indicating light of the first nanosecond laser and the second nanosecond laser, and moving the position of the sample to be detected on the object carrying lifting table to enable the area to be detected on the sample to be detected to fall on the midpoint position of the light focusing spots of the two lasers; and setting parameters of a programmable pulse delay generator, changing the time delay of the light-emitting signal of the first nanosecond laser and an ICCD gate width signal, and further finely adjusting the lifting of the object lifting table by a computer, so that a spectrogram observed on software of the computer is a linear radiation spectrogram with a good effect, and the acquired spectral line intensity is maximum.

Exemplarily, as shown in fig. 4, a plasma radiation spectrum line comparison graph of a collinear double-pulse fiber LIBS enhanced spectrum and a single-pulse fiber LIBS spectrum is shown, where the collinear double-pulse fiber laser LIBS spectrum is shown by a solid line, and the single-pulse fiber laser LIBS spectrum is shown by a dashed line. In a collinear double-pulse fiber LIBS mode, the laser energy of a main pulse and the laser energy of a secondary pulse are both 12mJ, and the time interval of the two pulses is 9 mu m; in the single pulse fiber LIBS mode, the pulse laser energy is 24 mJ. It can be seen that compared with the detection system using the collinear double-pulse fiber LIBS mode, the LIBS spectral signals (including characteristic spectral lines and background spectral lines) in the sample are integrally enhanced, and the enhancement amplitudes of the characteristic lines of different elements are different from 1.2 times to 3 times, so that the detection sensitivity and the element detection limit are improved.

The third aspect of the present application also includes a computer program product which, when run, causes a computer to perform the method of any of the second or third aspects. Specifically, the method includes the steps of enabling a computer to execute instructions for opening or closing a movable door in the fiber LIBS probe in S1, and controlling the ascending, descending and suspending of an object lifting platform; executing an instruction for monitoring the output laser energy of the first nanosecond laser and the second nanosecond laser; setting double-pulse targeting times, setting an LIBS spectrum detection mode and setting an ICCD gate width signal; executing an instruction for switching four pulse fiber LIBS modes; instructions to turn the ICCD, spectrometer, and computer software on or off are executed. The operation is controlled by a computer program product, so that the labor is well saved, each link and step are accurately controlled, and the method and the device are well matched to complete the optical fiber LIBS detection in the selectable double-pulse mode.

A fourth aspect of the present application also includes a computer storage medium comprising computer instructions which, when the storage medium is instructed to run on a computer, cause the computer to perform the method of any of the second or third aspects. The storage medium is used for storing some data and instructions loaded in the computer and classifying and sorting the data, and when the computer needs to use a certain item or some data, the data can be directly called from the storage medium, so that the operation is convenient and fast. The storage medium is specifically used for storing all double-pulse targeting times, characteristic radiation spectrograms obtained at each time and spectrograms of elements of a standard sample in each complete selectable double-pulse mode fiber LIBS detection process. The instructions comprise instructions for opening or closing a movable door in the fiber LIBS probe and executing control of ascending, descending and suspending of an object lifting platform; executing an instruction for monitoring the output laser energy of the first nanosecond laser and the second nanosecond laser; setting double-pulse targeting times, setting an LIBS spectrum detection mode and setting an ICCD gate width signal; executing an instruction for switching four pulse fiber LIBS modes; instructions to turn the ICCD, spectrometer, and computer software on or off are executed.

A fifth aspect of the present application also includes an apparatus comprising a processor configured to couple with the storage medium and read instructions from the storage medium, and to execute the method according to any one of the second aspect or the second aspect. The processor reads instructions including opening or closing a movable door in the fiber LIBS probe and executing control of ascending, descending and suspending of an object lifting platform; executing an instruction for monitoring the output laser energy of the first nanosecond laser and the second nanosecond laser; setting double-pulse targeting times, setting an LIBS spectrum detection mode and setting an ICCD gate width signal; executing an instruction for switching four pulse fiber LIBS modes; instructions to turn the ICCD, spectrometer, and computer software on or off are executed.

The application provides a fiber LIBS detection system with selectable double-pulse mode, which comprises: the system is applied to set the time delay between a main pulse and a secondary pulse through a programmable pulse delay generator according to actual requirements and set the time delay of an ICCD collected spectrum, an oscilloscope is used for observing whether the time delay of each path of signal is accurate or not, and a spectrometer collects the spectrum and performs light splitting treatment on the spectrum after the ICCD starts to work; setting the accumulation times of double-pulse target shooting in the software of a computer; the spectrometer samples the environmental background spectrum before each target shooting; after the double-pulse fiber laser targeting is finished, the spectrometer accumulatively transmits the collected multiple spectra to the computer; the software on the computer analyzes and compares the acquired spectral data with LIBS element spectral information in an NIST database to obtain the element types and corresponding spectral line information contained in the sample to be detected, and can further perform a double-pulse fiber laser targeting experiment of a standard sample. The method has the advantages of reducing the influence of matrix effect on detection, along with high repeatability, high spectral signal-to-noise ratio, high analysis speed, safe and reliable measurement process, high element detection limit and capability of remote online monitoring. The method solves the problems that the traditional optical fiber LIBS is easily influenced by the matrix effect of a sample, and has the defects of poor laser pulse stability, poor repeatability, unrepeatable ablation process, noise interference generated by a detector, high detection limit, unobvious non-metal element characteristic spectral line, difficulty in quantitative analysis and the like.

It is noted that relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The above description is merely exemplary of the present application and is presented to enable those skilled in the art to understand and practice the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

It will be understood that the present application is not limited to what has been described above and shown in the accompanying drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the application is limited only by the appended claims.

Claims (7)

1. A selectable double-pulse mode fiber LIBS detection system, the system comprising: an integrated optical fiber device, an optical fiber LIBS probe, a control detection module and an optical fiber transmission module,

a programmable pulse delay generator (33) in the control detection module is electrically connected with a control end of a first nanosecond laser (11) and a control end of a second nanosecond laser (19) in the integrated optical fiber device respectively;

a computer (31) in the control detection module is respectively and electrically connected with a monitoring end of a first laser energy meter (15), a monitoring end of a second laser energy meter (111) and a signal control end of a light shielding plate (117) in the integrated optical fiber device;

an oscilloscope (32) in the control detection module is respectively and electrically connected with a monitoring end of a first photoelectric detector (12) and a monitoring end of a second photoelectric detector (110) in the integrated optical fiber device;

a main probe (22) in the optical fiber LIBS probe is respectively connected with a main pulse laser output end of the integrated optical fiber device and a spectrometer (34) in the control detection module through a first transmission optical fiber (41) and a third transmission optical fiber (43) in the optical fiber transmission module, and an auxiliary probe (24) in the optical fiber LIBS probe is connected with an auxiliary pulse laser output end of the integrated optical fiber device through a second transmission optical fiber (42) in the optical fiber transmission module;

the positions of a photoelectric switch transmitting end (26) and a photoelectric switch receiving end (28) in the optical fiber LIBS probe are arranged at the same height of the bracket (21);

the main probe (22) is fixedly connected with the guide rail (23), and the auxiliary probe (24) is connected with the guide rail (23) in a sliding manner;

the included angle between the optical axes of the laser output by the main probe (22) and the auxiliary probe (24) ranges from 45 degrees to 90 degrees.

2. The system according to claim 1, wherein the center of the main pulse laser output end of the integrated fiber optic device is collinear with the centers of the first fiber optic adapter (221), the third plano-convex lens (224), the fourth plano-convex lens (225) and the dichroic mirror (226) in the fiber optic LIBS probe.

3. The system of claim 1, wherein the center of the secondary pulse laser output end of the integrated fiber optic is collinear with the centers of the third fiber optic adapter (241), the seventh plano-convex lens (242), and the eighth plano-convex lens (243) in the fiber optic LIBS probe.

4. The system according to claim 1, wherein the center of the output end of the third transmission fiber (43) is aligned with the centers of the second fiber adapter (222), the fifth plano-convex lens (227), the sixth plano-convex lens (228) and the reflector (229) in the fiber LIBS probe, and antireflection films are coated on the surfaces of the fifth plano-convex lens (227) and the sixth plano-convex lens (228).

5. The system of claim 1, wherein the detection modes available from the system include four modes, a collinear double pulse LIBS mode, a cross double pulse LIBS mode, a reheat quadrature double pulse LIBS mode, and a pre-ablation quadrature double pulse LIBS mode.

6. A method for fiber LIBS detection in selectable double-pulse mode, the method being applied to the system according to any one of claims 1 to 5, wherein the method comprises:

s1, opening a movable door (27) in the fiber LIBS probe, placing the sample to be tested on an object carrying lifting table (25) in the fiber LIBS probe and closing the movable door (27);

s2, the object carrying lifting table (25) is lifted to drive the sample to be detected to slowly rise until the upper surface of the sample to be detected shields a light beam emitted by a photoelectric switch emitting end (26) in the optical fiber LIBS probe, and then the sample to be detected stops rising;

s3, opening the indicating light of a first nanosecond laser (11) and a second nanosecond laser (19) in the integrated optical fiber device, adjusting the position of the sample to be detected on the object lifting table (25), and enabling the area to be detected on the sample to be detected to fall on the midpoint position of the indicating light focusing light spots of the first nanosecond laser (11) and the second nanosecond laser (19);

s4, adjusting the emitting laser parameters of the first nanosecond laser (11), the gate width signal delay of the ICCD (35) and the position of the object lifting table (25);

s5, observing the signal-to-back ratio of the characteristic radiation spectrum and the ordinate of the spectrogram, if the signal-to-back ratio is high and the ordinate of the spectrogram has the maximum value, performing the step S6, if the signal-to-back ratio is low, returning to the step S4, and performing the step S6 until the characteristic radiation spectrum with the high signal-to-back ratio and the ordinate of the spectrogram has the maximum value is observed;

s6, switching four double-pulse fiber LIBS modes and setting double-pulse targeting accumulation times;

s7, sampling background light by using a spectrometer (34) in the control detection module to obtain the accumulated spectrum information of the sample to be detected;

s8, comparing the spectrum data in the database to obtain characteristic spectral lines corresponding to the element types in the sample to be detected;

s9, further performing a double-pulse fiber LIBS experiment on the standard sample, and quantitatively detecting the element content in the sample to be detected through an LIBS element calibration curve;

and S10, lowering the object lifting platform (25) to the bottommost part.

7. Method according to claim 6, characterized in that the control accuracy of the object table (25) is 10 μm.

Images