Ultra-wide spectrum three-pulse LIBS detection system and method for target component detection

Abstract

The present invention discloses an ultra-wide spectrum three-pulse LIBS detection system and method for target component detection, which belongs to the field of laser detection technology. The system is mainly composed of a laser component; a primary laser beam expansion and beam combining optical component; a large dynamic adaptive transceiver multiplexing optical component; a spectrum-full waveform detection optoelectronic component; and an acquisition and industrial control component. In the present invention, a three-pulse output design of a high-energy single-wavelength pulse laser and a wide-spectrum tunable OPO laser combined light source is adopted. The plasma is excited by a single-wavelength high-energy laser pulse, and the plasma is synchronously heated by a double pulse output by a wide-spectrum tunable OPO light source. The output wavelength is more flexible, and while heating a wider LIBS spectrum line, the stability of the LIBS spectrum within a larger dynamic distance can be improved, thereby increasing the signal-to-noise ratio of longer-distance detection.

Description

Technical Field

[0001] The present invention belongs to the field of laser detection technology, and in particular relates to an ultra-wide spectrum three-pulse LIBS detection system and method for target component detection. Background Art

[0002] Laser induced breakdown spectroscopy (LIBS) detection technology uses high-power density laser pulses to focus on the sample surface, and forms high-temperature and high-pressure plasma through the interaction between laser and matter. It collects and analyzes the atomic and particle spectra emitted by the plasma during the cooling process to detect the type and concentration of elements in the sample. It has the advantages of non-contact, low destructiveness, high speed, and simultaneous online monitoring of multiple elements.

[0003] A typical LIBS detection system generally consists of: laser light source, transceiver optical module, spectral spectrometry and detection module, timing control module and industrial computer module. The laser light source is used to generate high-energy pulsed laser, the transceiver optical module is used to realize the focusing of high-energy laser pulses on the sample surface to generate plasma and collect plasma spectrum signals, the spectral spectrometry and detection module is responsible for converting the collected signal light into spectral wavelength and intensity data, the timing control module and the industrial computer module work together to achieve precise control of the laser light output and the working timing of the spectral spectrometry and detection module, reduce the influence of bremsstrahlung and compound radiation, and prevent signal background interference, and output the measurement results by writing the analysis method program.

[0004] At present, there are two main solutions for LIBS systems: single pulse zoom detection and dual pulse fixed focus spectral enhancement detection. Among them, the single pulse zoom detection technology mainly uses a single single wavelength pulse laser in conjunction with a coaxial zoom transceiver optical system, a spectral detection module, and an industrial control module to perform LIBS detection in scenes with dynamic distance changes; the dual pulse fixed focus spectral enhancement detection technology uses two pulse lasers with fixed emission wavelengths in conjunction with a transceiver separation optical system, a spectral detection module, and an industrial control module to achieve high-quality detection of spectral data in terms of intensity and stability. At this stage, the LIBS system is still constrained by limited detection of industrial scenes, which is mainly manifested in:

[0005] 1. Based on the single-pulse remote zoom optical path multiplexing LIBS measurement system, the remote LIBS signal acquisition can be realized, but the single-pulse LIBS cannot avoid the disadvantages of poor spectral signal quality and poor detection ability, which are manifested in the low stability of signal spectral intensity, poor signal-to-background intensity ratio, low ablation efficiency and measurement accuracy, which is extremely unfriendly to remote LIBS detection; at the same time, the remote zoom is mainly controlled manually, and it is impossible to complete adaptive feedback zoom control according to the target scene; without obtaining the precise distance information of the target, the focusing effect of manual zoom is limited, and the optimal zoom must be based on accurate distance measurement information to obtain a better LIBS effect; and the transmission zoom has complex requirements on the lens coating process and high cost.

[0006] 2. The LIBS measurement system based on dual-pulse laser can improve the spectral signal-to-background ratio, element detection capability and detection line of plasma signal light, and can be used to a certain extent for the detection of material composition content. However, the dual-pulse systems reported so far are mostly short-range detection with a fixed focal length, which cannot meet the requirements of large dynamic working distances in industrial sites; the dual-pulse laser wavelength is fixed, and it is impossible to flexibly match the wavelengths of the excitation pulse and the enhancement pulse to achieve optimal spectral enhancement capability matching; the dual-pulse LIBS systems based on tunable lasers reported so far are fixed-focus, short-range detection, and there are no reports of systems with adaptive, long-range detection capabilities.

[0007] 3. For single-pulse and double-pulse LIBS detection modes, there are no reports on systems that can adaptively acquire LIBS signals with large dynamic distances and high stability, which cannot meet the needs of intelligent and automated remote LIBS detection in industrial sites. Summary of the invention

[0008] In view of the above technical problems, the present invention proposes an ultra-wide spectrum three-pulse LIBS detection system and method for target component detection.

[0009] The first aspect of the present invention discloses an ultra-wide spectrum three-pulse LIBS detection system for target component detection, the system comprising: a laser component, a first-level laser beam expansion and beam combining optical component; a large dynamic adaptive transceiver multiplexing optical component, a spectrum-full waveform detection optoelectronic component, and a collection and industrial control component; wherein:

[0010] The laser assembly provides high-energy laser pulses for remote induced breakdown of plasma and wide-spectrum laser pulses for remote secondary heating of plasma targets; the laser assembly includes: two special solid-state lasers, one of which is a high-energy nanosecond Nd:YAG pulse solid-state laser for providing the high-energy laser pulses, and the other is a high-energy wide-spectrum tunable OPO pulse solid-state laser for providing the wide-spectrum laser pulses;

[0011] The laser beams emitted by the laser assembly are expanded and combined by the first-level laser beam expansion and combination optical component, the field of view angle and divergence angle are compressed, and the pitch, azimuth and emission angle are adjusted; the first-level laser beam expansion and combination optical component includes: a transmission beam expander, a first off-axis beam expander, a second off-axis beam expander, a first plane reflector, a second plane reflector, a first plane beam combination mirror, and a second plane beam combination mirror;

[0012] The large dynamic adaptive transceiver multiplexing optical component performs secondary beam expansion and focusing processing on the laser beam after the primary beam expansion, and receives the echo signal; the large dynamic adaptive transceiver multiplexing optical component includes: a focal length adjustable card telescope, a transceiver integrated plane beam combiner, an electric adjustment mechanism, a first conical mirror, a second conical mirror, and a plane beam splitter;

[0013] The spectrum detection of remote induced breakdown plasma and the photoelectric detection of target multi-spectral scattered echo signals are performed by the spectrum-full waveform detection optoelectronic assembly; the spectrum-full waveform detection optoelectronic assembly includes: a first off-axis metal reflector, a second off-axis metal reflector, an ICCD type spectrometer, a first multi-mode optical fiber, a second multi-mode optical fiber, a CT type grating optical system, a one-dimensional optical fiber array, an optical fiber array connector, and a high-speed APD array;

[0014] The acquisition and industrial control components control the components in the system to work according to the pre-configured programs and invert and output the detection data; the acquisition and industrial control components include: multi-channel high-speed acquisition cards and industrial computers; used to realize the acquisition and processing of pulse laser echo waveforms, the analysis of LIBS spectral signals, and the large dynamic adaptive control and adjustment of the laser focus point.

[0015] The system according to the first aspect of the present invention, for a laser assembly, wherein:

[0016] The high-energy nanosecond Nd:YAG pulse solid-state laser provides high-energy laser pulses with a central wavelength of 1064nm, a single pulse energy of 850mJ, and a pulse width of less than 9ns;

[0017] The high-energy wide-spectrum tunable OPO pulse solid-state laser is pumped by a 532nm intermediate frequency laser and includes two pulse output ports: signal light and idler light. The wide-spectrum laser pulse tunable spectral range is 680nm-2000nm and the pulse width is less than 6ns.

[0018] According to the system of the first aspect of the present invention, for a first-stage laser beam expansion and beam combining optical component, wherein:

[0019] The transmissive beam expander is coated with a 1064nm anti-reflection film and is used to compress the field angle of the laser beam emitted by a high-energy nanosecond Nd:YAG pulse solid laser. It adopts a transmissive optical structure.

[0020] The first off-axis beam expander is coated with a metal aluminum film, which is highly reflective in the 1100nm-2000nm band and adopts a reflective structure. It is used to compress the beam divergence angle of the signal light channel of the high-energy, wide-spectrum tunable OPO pulse solid laser and eliminate optical chromatic aberration.

[0021] The second off-axis beam expander is coated with a metal aluminum film, which is highly reflective in the 680nm-1000nm band and adopts a reflective structure. It is used to compress the beam divergence angle of the idler optical signal channel of the high-energy, wide-spectrum tunable OPO pulse solid-state laser and eliminate optical chromatic aberration.

[0022] The first plane reflector is coated with a 1100nm-2000nm high-reflection dielectric film to adjust the pitch and azimuth, and adjust the idler light beam and the signal light beam to be coaxial;

[0023] The second plane reflector is coated with a broadband high-reflection film, with a reflectivity greater than 94% in the range of 680-2000nm, and can adjust the pitch and azimuth;

[0024] The first plane beam combiner adjusts the pitch and azimuth, and adjusts the output angle of the signal beam expansion light. Special wide-spectrum coating is performed on the front and back sides. The back side has high transmittance to the 1100nm-2000nm idler beam expansion light, and the front side has high reflection to the 680nm-1000nm band and high transmittance to the 1100nm-2000nm band.

[0025] The second plane beam combiner adjusts the pitch and azimuth, and adjusts the output angle of the 1064nm high-energy expanded beam. Special wide-spectrum coating is performed on the front and back sides. The back side has high transmittance to the 680nm-2000nm band, and the front side has high transmittance to the 680nm-2000nm band and high reflectivity to the 1064nm laser beam alone. The reflectivity bandwidth is not less than 10nm.

[0026] According to the system of the first aspect of the present invention, for a large dynamic adaptive transceiver multiplexing optical component, wherein:

[0027] The front and back sides of the transceiver integrated plane beam combiner are coated in different areas; the back side is coated with a 680nm-2000nm anti-reflection dielectric film with a transmittance greater than 94%; the front elliptical area is coated with a 680nm-2000nm anti-reflection dielectric film, and the rest of the area is coated with a metal aluminum film;

[0028] The focal length adjustable card telescope is used to realize the convergence of the emitted laser pulse at the target and receive the target scattered signal. The receiving primary mirror is coated with a metal aluminum film to receive the echo signal. The receiving secondary mirror adopts regional coating. The circular area is coated with a 680nm-2000nm high-reflective dielectric film, and the rest of the area is coated with a metal aluminum film.

[0029] The outgoing laser beam from the transceiver integrated plane beam combiner is incident on the high-reflection dielectric film-coated area of ​​the receiving secondary mirror. The off-axis of the card telescope is used to achieve spatial focusing of the beam. The echo signal is received by the overall optical area of ​​the telescope and reflected by the transceiver integrated plane beam combiner into the conical mirror pair for beam shaping.

[0030] The conical mirror pair consists of two conical mirrors of different sizes, which are used to shrink the echo signal, reduce the collimation aperture of the optical path, and convert the echo signals of different bands into Bessel beams;

[0031] The plane beam splitter separates the LIBS signal and the outgoing laser signal by coating. The coating layer increases the transmittance of the LIBS signal of 200nm-500nm and has high reflectivity for the outgoing laser wavelength of 680nm-2000nm.

[0032] According to the system of the first aspect of the present invention, for the spectrum-full waveform detection optoelectronic component, wherein:

[0033] The first off-axis metal reflector is made of metal aluminum and adopts an aspherical design. It converges the LIBS signal light passing through the plane beam splitter into the first multimode optical fiber, which guides the light into the ICCD spectrometer for LIBS spectral signal analysis.

[0034] The second off-axis metal reflector is made of metal aluminum and adopts an aspherical design to couple and converge the three-pulse echo laser signal to the second multimode optical fiber, and the second multimode optical fiber is connected to the CT-type grating optical system;

[0035] The CT grating optical system separates the target scattered laser pulse signal in space according to the spectrum, and the spectrum splitting range is 800nm-1600nm; the one-dimensional fiber array is used to receive the spatial splitting signal, and the fiber array connector is used to connect the one-dimensional fiber array and the high-speed APD array;

[0036] The high-speed APD array adopts a time-division multiplexing design and is used to detect the echo signal waveform of the laser emitted by the 1064nm laser and the OPO laser. The high-speed APD array consists of multiple fiber APDs and a 1×3 multimode fiber beam splitter. The beam combining end of the 1×3 multimode fiber beam splitter is connected to the fiber APD. The fiber APD bandwidth meets the laser pulse width detection requirements. The lengths of the three splitting fibers at the splitting end differ by a distance of the laser pulse width and are respectively connected to the fiber array end.

[0037] According to the system of the first aspect of the present invention, for the acquisition and industrial control component, wherein:

[0038] The multi-channel acquisition card has multiple acquisition channels matching the number of fiber APDs, and the bandwidth is not less than the fiber APD bandwidth;

[0039] The industrial computer is used to obtain data from the spectrometer and acquisition card, analyze the LIBS spectrum signal and target distance information, and the industrial computer is integrated with a laser trigger control module to control the high-energy nanosecond Nd:YAG pulse solid laser and the high-energy wide-spectrum tunable OPO pulse solid laser to work at different delays, and perform secondary enhancement on the LIBS spectrum signal.

[0040] The industrial computer also feeds back to the electric adjustment mechanism, controls the movement and focusing of the secondary mirror of the receiving telescope based on the multi-spectral measured information, achieves adaptive focusing of the laser spot at the optimal position, and instructs the laser light to calibrate the position of the three-pulse outgoing laser optical axis.

[0041] The second aspect of the present invention discloses an ultra-wide spectrum three-pulse LIBS detection method for target component detection, which utilizes the ultra-wide spectrum three-pulse LIBS detection system described in the first aspect of the present invention to achieve target component detection.

[0042] In summary, the present invention proposes a precise adaptive, large dynamic ultra-wide spectrum three-pulse LIBS detection system for target component detection based on the needs of accurate and automated detection in industrial sites. In the technical solution of the present invention, a three-pulse output design of a high-energy single-wavelength pulse laser and a wide-spectrum tunable OPO laser combined light source is adopted. The plasma is excited by a single-wavelength high-energy laser pulse, and the plasma is synchronously heated by a double pulse output by a wide-spectrum tunable OPO light source. The output wavelength is more flexible, and while heating a wider LIBS spectrum line, the stability of the LIBS spectrum within a larger dynamic distance can be improved, thereby increasing the signal-to-noise ratio of longer-distance detection.

[0043] In the technical solution of the present invention, the beam combining mirror and the secondary mirror of the telescope in the transceiver optical structure adopt a zoned coating design and a transmit-receive integrated off-coaxial reflective structure design, which can meet the large dynamic spectral range of operation while sharing the telescope transmission and reception, avoid the consistency adjustment of the transmitting and receiving optical axes, improve the pointing accuracy and integration of the system, and reduce the difficulty and cost of adjustment; the telescope primary mirror can be coated with a metal aluminum film to achieve efficient collection of LIBS signals and laser signals, avoiding the need for complex dielectric film coating on the receiving mirror in a transmission structure, thereby reducing costs.

[0044] In the technical solution of the present invention, the post-receiving optical path part adopts a conical mirror combination design, and the received LIBS wide-spectrum collimated beam and the target scattered laser pulse collimated beam are converted and reduced through near-Bessel beam conversion, so that the echo signal energy is more concentrated and uniform, and the signal-to-noise ratio of remote detection of LIBS signals using an ICCD spectrometer is improved.

[0045] In the technical solution of the present invention, distance detection adopts tunable three-wavelength synchronous detection based on a wide-spectrum tunable OPO light source and a high-energy excitation laser pulse light source, and the ranging accuracy is improved by a multi-spectral waveform correction method.

[0046] In the technical solution of the present invention, multi-spectral distance detection adopts a fiber time-division multiplexing design based on a CT-type grating splitting structure, and uses the same photodetector to achieve single synchronous reception of three-pulse echo waveforms, avoiding inconsistent waveform responses caused by different bandwidths when using multiple detectors to detect different wavelengths, thereby improving ranging accuracy. At the same time, one detector is used for multi-wavelength waveform detection, which reduces costs and improves the integration and stability of the system.

[0047] In the technical solution of the present invention, based on the precise ranging information of the multi-spectrum, the control system feeds back to the secondary mirror adjustment mechanism, adjusts the position of the secondary mirror so that the outgoing light beam converges to the optimal LIBS spot, and combines the OPO light source double-pulse LIBS signal enhancement effect to ensure the precise adaptive, intelligent and stable acquisition of remote LIBS signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0049] Figure 1 A schematic diagram of an ultra-wide spectrum three-pulse LIBS detection system for target component detection according to an embodiment of the present invention;

[0050] Figure 2 is a schematic diagram of a transceiver-integrated plane mirror according to an embodiment of the present invention;

[0051] Figure 3 is a schematic diagram of a receiving secondary mirror according to an embodiment of the present invention;

[0052] Figure 4 A schematic diagram of an off-axis focusing optical path of an outgoing laser according to an embodiment of the present invention;

[0053] Figure 5 A schematic diagram of LIBS dynamic detection adaptive control according to an embodiment of the present invention;

[0054] Figure 6 Schematic diagram of an accurate adaptive, ultra-wide spectrum three-pulse LIBS detection system for target component detection within a dynamic distance of 1m-50m according to an embodiment of the present invention.

[0055] in:

[0056] 1- High energy nanosecond solid laser (high energy Nd:YAG nanosecond solid laser);

[0057] 2-tunable OPO pulsed solid-state laser;

[0058] 3-off-axis beam expander 1;

[0059] 4-off-axis beam expander 2;

[0060] 5-Indicator laser;

[0061] 6- plane reflector 1;

[0062] 7- plane beam combiner 1;

[0063] 8- Transmission beam expander;

[0064] 9- plane beam combiner 2;

[0065] 10- plane reflector 2;

[0066] 11-transmitting and receiving integrated plane mirror;

[0067] 12-receiving primary mirror;

[0068] 13-Electric adjustment mechanism;

[0069] 14-receiving secondary mirror;

[0070] 15-conical mirror 1;

[0071] 16-conical mirror 2;

[0072] 17- plane beam splitter;

[0073] 18-off-axis metal reflector 1;

[0074] 19-off-axis metal reflector 2;

[0075] 20-multimode optical fiber 1;

[0076] 21- multimode optical fiber 2;

[0077] 22-CT type grating optical system;

[0078] 23-ICCD spectrometer;

[0079] 24-One-dimensional fiber array;

[0080] 25-fiber array connector;

[0081] 26-High-speed APD array;

[0082] 27-High-speed acquisition card;

[0083] 28-Industrial Computer. DETAILED DESCRIPTION

[0084] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0085] First embodiment

[0086] This embodiment relates to an accurate adaptive, large dynamic and ultra-wide spectrum three-pulse LIBS detection system for target component detection, such as Figure 1 As shown, it is mainly composed of laser components; first-level laser beam expansion and beam combining optical components; large dynamic adaptive transceiver multiplexing optical components; spectrum-full waveform detection optoelectronic components; and collection and industrial control components.

[0087] The laser assembly is mainly composed of two special solid lasers, one is a high-energy nanosecond Nd:YAG pulse solid laser, and the other is a high-energy wide-spectrum tunable OPO pulse solid laser. Among them, the high-energy nanosecond Nd:YAG solid laser has a central wavelength of 1064nm, a single pulse energy of up to 850mJ, and a pulse width of less than 9ns; the wide-spectrum tunable OPO pulse solid laser uses a 532nm intermediate frequency laser for pumping, and has a tunable spectrum range of 680nm-2000nm, including two pulse output ports for signal light and idler light, with a narrow line width and a pulse width of less than 6ns.

[0088] The primary laser beam expansion and beam combining optical components are composed of: a transmission beam expander, an off-axis beam expander 1, an off-axis beam expander 2, a plane reflector 1, a plane beam combiner 1, a plane beam combiner 2 and a plane reflector 2. Among them, the transmission-type beam expander is coated with a 1064nm anti-reflection film, which is used to perform primary compression on the field angle of the laser beam emitted by the high-energy nanosecond Nd:YAG pulse laser. The transmission-type optical structure is used to reduce costs and has a compact structure. The off-axis beam expander 1 is coated with a metal aluminum film, which can have high reflection in the 1100nm-2000nm band, and adopts a reflective structure, which is used for the OPO laser signal light channel beam divergence angle compression and optical chromatic aberration elimination. The off-axis beam expander 2 is coated with a metal aluminum film, which is used for high reflection in the 680nm-1000nm band, and adopts a reflective structure for the OPO laser idler light signal channel beam divergence angle compression and chromatic aberration elimination. The plane reflector 1 is coated with a 1100nm-2000nm high-reflection dielectric film, and has the functions of pitch and azimuth adjustment, which can adjust the idler light beam and the signal light beam to be coaxial. The plane beam combiner 1 has the functions of pitch and azimuth adjustment, which is used to adjust the output angle of the signal beam expander, and is used as the core module in the component. One of the components, with special wide-spectrum coating on both the front and back sides, the back side has high transmittance to 1100nm-2000nm idler expanded light, the front side has high reflection to 680nm-1000nm band, and at the same time has high transmittance to the spectrum in the range of 1100nm-2000nm; the plane beam combiner 2 has the functions of pitch and azimuth adjustment, which is used to adjust the output angle of 1064nm high-energy expanded light. As one of the core modules in this component, special wide-spectrum coating is carried out on both the front and back sides, the back side has high transmittance to 680nm-2000nm, the front side has high transmittance to 680nm-2000nm band, and at the same time has high reflection to 1064nm laser beam alone, and the reflectivity bandwidth can be not less than 10nm; the plane reflector 2 is coated with a broadband high-reflection film, and the reflectivity in the range of 680-2000nm is greater than 94%. It has the functions of pitch and azimuth adjustment, which can realize fine adjustment of the combined beam, and enter the large dynamic adaptive transceiver optical component.

[0089] The large dynamic adaptive transceiver multiplexing optical component consists of: a focal length adjustable card telescope, a transceiver integrated plane mirror, an electric adjustment mechanism, a conical mirror 1, a conical mirror 2 and a plane beam splitter. Among them, the front and back sides of the transceiver integrated plane beam combiner are coated in different areas. The back side is coated with a 680nm-2000nm anti-reflection dielectric film with a transmittance greater than 94%. The elliptical area on the front side is coated with a 680nm-2000nm anti-reflection dielectric film, and the rest of the area is coated with a metal aluminum film, such as Figure 2 As shown; the focal length adjustable cassette telescope is used to emit laser pulses to converge at the target and receive the target scattered signal. The receiving primary mirror has a large aperture and is coated with a metal aluminum film. It is used to receive echo information at a long distance with a high signal-to-noise ratio. The receiving secondary mirror adopts regional coating. The small circular area is coated with a 680nm-2000nm high-reflective dielectric film, and the remaining area is coated with a metal aluminum film. Figure 3As shown, the outgoing laser beam from the transceiver integrated plane mirror is incident on the high-reflection dielectric film-coated area of ​​the receiving secondary mirror, and the off-axis function of the cassette telescope is used to achieve spatial focusing of the beam, as shown in FIG. Figure 4 As shown, the echo signal is received by the overall optical area of ​​the telescope, and is reflected by the transceiver integrated plane mirror into the conical mirror pair for beam shaping; the conical mirror pair consists of two conical mirrors 1 and 2 of different sizes, and mainly realizes two functions: one is to shrink the echo signal and reduce the collimation aperture of the rear optical path, and the other is to convert the live wave signals of different bands into near-Bessel beams, so that the receiving system has higher optical efficiency and the optical structure is simpler; the plane beam splitter separates the LIBS signal and the outgoing laser signal by coating, and the film layer increases the transmittance of the LIBS signal (200nm-500nm) and has high reflection to the outgoing laser wavelength (680nm-2000nm).

[0090] The spectral-full waveform detection optoelectronic system consists of an off-axis metal reflector 1, an off-axis metal reflector 2, an ICCD spectrometer, multimode optical fibers 1 and 2, a CT grating optical system, a one-dimensional optical fiber array, an optical fiber array converter, and a high-speed APD array. The off-axis metal reflector is made of aluminum and has an aspheric design. It efficiently converges the LIBS signal light that passes through the plane beam splitter into the multimode optical fiber 1, which is then guided by the multimode optical fiber 1 into the ICCD spectrometer for LIBS spectral signal analysis. The ICCD mid-step spectrometer has high photon sensitivity and can achieve high signal-to-noise ratio reception of long-distance weak LIBS echo signals. The off-axis metal reflector 2 is also made of aluminum and has an aspheric design. It efficiently couples the three-pulse echo laser signal into the multimode optical fiber 2. The multimode optical fiber 2 is connected to the CT grating optical system. The CT grating optical system The target scattered laser pulse signal is separated in space according to the spectrum, and the spectral splitting range is 800nm-1600nm; the one-dimensional fiber array is used to receive the spatial splitting signal, and the fiber array connector is used to connect the one-dimensional fiber array and the high-speed APD array; the high-speed APD array adopts a time-division multiplexing design to detect the echo signal waveform of the laser emitted by the 1064nm laser and the OPO laser, reduce the number of detectors and the difference in waveform response of different detectors, improve the accuracy of distance correction of multi-spectral data, and improve the system integration. The high-speed APD array is composed of multiple fiber APDs and a 1×3 multimode fiber splitter. The beam combining end of the 1×3 multimode fiber splitter is connected to the fiber APD. The fiber APD bandwidth meets the laser pulse width detection requirements. The lengths of the three splitting fibers at the splitting end differ by a distance length of the laser pulse width, and are respectively connected to the fiber array end.

[0091] The acquisition and industrial control system consists of a multi-channel high-speed acquisition card and an industrial computer, which is used to realize the acquisition and processing of pulse laser echo waveforms, the analysis of LIBS spectral signals, and the large-dynamic adaptive control and adjustment of laser focusing points. Among them, the multi-channel acquisition card has multiple acquisition channels to match the number of optical fiber APDs, and the bandwidth is not less than the APD bandwidth; the industrial computer is used to obtain data from the spectrometer and acquisition card, invert LIBS spectral information and precise target distance information, and at the same time, the industrial computer is integrated with a laser trigger control module to control the high-energy Nd:YAG pulse laser and tunable OPO laser to work at different delays to achieve the secondary enhancement effect of the LIBS signal. The industrial computer also feeds back to the electric adjustment mechanism to accurately control the movement and focusing of the secondary mirror of the receiving telescope based on the multi-spectral measured information to achieve adaptive focusing of the laser spot at the optimal position. The system indication laser light is used in the equipment preparation work to calibrate the position of the three-pulse outgoing laser optical axis. The specific adaptive control flow chart is as follows Figure 5 shown.

[0092] Second embodiment

[0093] This embodiment relates to an embodiment of a precise adaptive, ultra-wide spectrum three-pulse LIBS detection system for target component detection within a dynamic distance of 1m-50m. It should include: laser components (high energy Nd:YAG laser, OPO tunable laser), primary laser beam expansion, beam combining optical components (1064nm transmission beam expander, off-axis beam expander 1, off-axis beam expander 2, plane reflector 1, plane beam combiner 1, plane beam combiner 2, plane reflector 2), large dynamic adaptive transceiver multiplexing optical components (240mm card-type focusing telescope, transceiver integrated plane mirror, conical mirror 1, conical mirror 2, plane beam splitter, electric adjustment mechanism), spectrum-full waveform detection components (off-axis aluminum metal mirrors 1 and 2, ICCD spectrometer, CT grating optical system, one-dimensional fiber array, fiber array connector, 1×3 fiber combiner, APD), acquisition and industrial control system (high-speed acquisition card, industrial control computer), and the indicator laser is a beam of 638nm continuous laser.

[0094] The indicator laser is illuminated to the target position after passing through plane reflector 1, plane beam combiner 1, 2, transceiver integrated plane mirror and cassette focusing telescope; the idler channel laser beam of OPO tunable laser is enlarged by 2.5 times after passing through off-axis beam expander 1, and the signal channel laser beam is also enlarged by 2.5 times after passing through off-axis beam expander 2; the expanded signal channel and idler channel lasers are combined by plane beam combiner 1; the 1064nm high energy laser pulse is expanded by 2.5 times by the transmission beam expander, and then The beam combiner 2 combines the three pulsed laser beams; the plane reflector 2 reflects the combined laser beam into the wide-spectrum anti-reflection coating area of ​​the transceiver plane mirror, and then enters the cassette focusing telescope, and finally converges to the target surface; the cassette focusing telescope has an aperture of 240mm and is used to receive the target LIBS signal and scattered laser echo signal with a high signal-to-noise ratio. After being reflected by the metal aluminum film coating area of ​​the transceiver plane mirror, it enters the conical mirror 1 and the conical mirror 2 and then collimated for output; the plane beam splitter transmits the LIBS signal light into the off-axis metal The metal mirror 1 and the off-axis aspheric metal mirror 1 merge the target LIBS signal into the input fiber port of the ICCD spectrometer for LIBS signal spectrum analysis; the pulse light signal is reflected by the plane beam splitter and enters the off-axis metal mirror 2, and then converges into the multimode optical fiber, and is introduced into the CT grating optical system through the multimode optical fiber to split the three-wavelength laser echo pulse light in space; the one-dimensional fiber array receives the three-wavelength light pulse signal, and according to the optical fiber interface corresponding to the wavelength of the three pulses of the output laser, the optical fiber splitting end of the 1×3 optical fiber combiner is connected to the spectral optical fiber position corresponding to the one-dimensional optical fiber array, and the optical fiber combining end is connected to the APD to detect the waveform of the three-pulse laser echo; the high-speed acquisition card acquires the APD output signal; the industrial computer analyzes and processes the output signal of the acquisition card to invert the target distance information, and at the same time feeds back the distance information to the electric adjustment mechanism to adjust the control position of the secondary mirror in real time to achieve the best focusing of the laser pulse, and the industrial computer simultaneously receives the output information of the ICCD spectrometer to invert the target composition, content and other information.

[0095] In summary, the present invention provides a three-pulse adaptive LIBS system with a large dynamic detection distance based on a wide-spectrum tunable OPO pulse laser and a high-energy Nd:YAG solid-state pulse laser. The system performs dual-pulse secondary plasma synchronous heating based on the dual-channel output laser of the wide-spectrum tunable OPO pulse laser, which can obtain better stability, especially for long-distance detection with a large dynamic distance, and can obtain a more stable spectral output than single-pulse secondary plasma heating.

[0096] The system uses a wide-spectrum tunable OPO laser light source to achieve more flexible wavelength tuning and a larger heating pulse spectrum tuning range, which can meet the acquisition of stable spectral lines of more components.

[0097] The system is based on multi-spectral time-division multiplexing of a CT-type grating optical structure. It can obtain more accurate ranging information while meeting the requirements of high integration and low cost. It is used for adaptive focusing of the outgoing laser and can achieve better laser spot convergence. Especially in the process of long-range LIBS detection, it can assist in achieving optimal LIBS excitation and secondary heating of the plasma.

[0098] The system adopts a reflective transceiver shared optical system and a zone coating design for the lens, which simplifies system integration, reduces costs, improves stability, and simplifies the difficulty of transceiver assembly and adjustment.

[0099] The system adopts a conical mirror group and lens area coating design, which can achieve higher optical efficiency in the acquisition of ultra-wide spectrum echo signals at the receiving end at a large dynamic detection distance, especially in long-range adaptive LIBS and ranging combined with multi-functional detection.

[0100] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above-mentioned embodiments only express several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, several variations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. An ultra-wide spectrum three-pulse LIBS detection system for target component detection, characterized in that: The system includes: a laser component, a first-level laser beam expansion and beam combining optical component; a large dynamic adaptive transceiver multiplexing optical component, a spectrum-full waveform detection optoelectronic component, and a collection and industrial control component; wherein: The laser assembly provides high-energy laser pulses for remote induced breakdown of plasma and wide-spectrum laser pulses for remote secondary heating of plasma targets; the laser assembly includes: two special solid-state lasers, one of which is a high-energy nanosecond Nd:YAG pulse solid-state laser for providing the high-energy laser pulses, and the other is a high-energy wide-spectrum tunable OPO pulse solid-state laser for providing the wide-spectrum laser pulses; The laser beams emitted by the laser assembly are expanded and combined by the first-level laser beam expansion and combination optical component, the field of view angle and divergence angle are compressed, and the pitch, azimuth and emission angle are adjusted; the first-level laser beam expansion and combination optical component includes: a transmission beam expander, a first off-axis beam expander, a second off-axis beam expander, a first plane reflector, a second plane reflector, a first plane beam combination mirror, and a second plane beam combination mirror; The large dynamic adaptive transceiver multiplexing optical component performs secondary beam expansion and focusing processing on the laser beam after the primary beam expansion, and receives the echo signal; the large dynamic adaptive transceiver multiplexing optical component includes: a focal length adjustable card telescope, a transceiver integrated plane beam combiner, an electric adjustment mechanism, a first conical mirror, a second conical mirror, and a plane beam splitter; The spectrum detection of remote induced breakdown plasma and the photoelectric detection of target multi-spectral scattered echo signals are performed by the spectrum-full waveform detection optoelectronic assembly; the spectrum-full waveform detection optoelectronic assembly includes: a first off-axis metal reflector, a second off-axis metal reflector, an ICCD type spectrometer, a first multi-mode optical fiber, a second multi-mode optical fiber, a CT type grating optical system, a one-dimensional optical fiber array, an optical fiber array connector, and a high-speed APD array; The acquisition and industrial control components control the components in the system to work according to the pre-configured programs and invert and output the detection data; the acquisition and industrial control components include: multi-channel high-speed acquisition cards and industrial computers; used to realize the acquisition and processing of pulse laser echo waveforms, the analysis of LIBS spectral signals, and the large dynamic adaptive control and adjustment of the laser focus point.

2. The ultra-wide spectrum three-pulse LIBS detection system for target component detection according to claim 1, characterized in that: For a laser assembly, where: The high-energy nanosecond Nd:YAG pulse solid-state laser provides high-energy laser pulses with a central wavelength of 1064nm, a single pulse energy of 850mJ, and a pulse width of less than 9ns; The high-energy wide-spectrum tunable OPO pulse solid-state laser is pumped by a 532nm intermediate frequency laser and includes two pulse output ports: signal light and idler light. The wide-spectrum laser pulse tunable spectral range is 680nm-2000nm and the pulse width is less than 6ns.

3. The ultra-wide spectrum three-pulse LIBS detection system for target component detection according to claim 2, characterized in that: For the first-stage laser beam expansion and combination optical components, where: The transmissive beam expander is coated with a 1064nm anti-reflection film and is used to compress the field angle of the laser beam emitted by a high-energy nanosecond Nd:YAG pulse solid laser. It adopts a transmissive optical structure. The first off-axis beam expander is coated with a metal aluminum film, which is highly reflective in the 1100nm-2000nm band and adopts a reflective structure. It is used to compress the beam divergence angle of the signal light channel of the high-energy, wide-spectrum tunable OPO pulse solid laser and eliminate optical chromatic aberration. The second off-axis beam expander is coated with a metal aluminum film, which is highly reflective in the 680nm-1000nm band and adopts a reflective structure. It is used to compress the beam divergence angle of the idler optical signal channel of the high-energy, wide-spectrum tunable OPO pulse solid-state laser and eliminate optical chromatic aberration. The first plane reflector is coated with a 1100nm-2000nm high-reflection dielectric film to adjust the pitch and azimuth, and adjust the idler light beam and the signal light beam to be coaxial; The second plane reflector is coated with a broadband high-reflection film, with a reflectivity greater than 94% in the range of 680-2000nm, and can adjust the pitch and azimuth; The first plane beam combiner adjusts the pitch and azimuth, and adjusts the output angle of the signal beam expansion light. Special wide-spectrum coating is performed on the front and back sides. The back side has high transmittance to the 1100nm-2000nm idler beam expansion light, and the front side has high reflection to the 680nm-1000nm band and high transmittance to the 1100nm-2000nm band. The second plane beam combiner adjusts the pitch and azimuth, and adjusts the output angle of the 1064nm high-energy expanded beam. Special wide-spectrum coating is performed on the front and back sides. The back side has high transmittance to the 680nm-2000nm band, and the front side has high transmittance to the 680nm-2000nm band and high reflectivity to the 1064nm laser beam alone. The reflectivity bandwidth is not less than 10nm.

4. The ultra-wide spectrum three-pulse LIBS detection system for target component detection according to claim 3, characterized in that: For a large dynamic adaptive transceiver multiplexing optical component, wherein: The front and back sides of the transceiver integrated plane beam combiner are coated in different areas; the back side is coated with a 680nm-2000nm anti-reflection dielectric film with a transmittance greater than 94%; the front elliptical area is coated with a 680nm-2000nm anti-reflection dielectric film, and the rest of the area is coated with a metal aluminum film; The focal length adjustable card telescope is used to realize the convergence of the emitted laser pulse at the target and receive the target scattered signal. The receiving primary mirror is coated with a metal aluminum film to receive the echo signal. The receiving secondary mirror adopts regional coating. The circular area is coated with a 680nm-2000nm high-reflective dielectric film, and the rest of the area is coated with a metal aluminum film. The outgoing laser beam from the transceiver integrated plane beam combiner is incident on the high-reflection dielectric film-coated area of ​​the receiving secondary mirror. The off-axis of the card telescope is used to achieve spatial focusing of the beam. The echo signal is received by the overall optical area of ​​the telescope and reflected by the transceiver integrated plane beam combiner into the conical mirror pair for beam shaping. The conical mirror pair consists of two conical mirrors of different sizes, which are used to shrink the echo signal, reduce the collimation aperture of the optical path, and convert the echo signals of different bands into Bessel beams; The plane beam splitter separates the LIBS signal and the outgoing laser signal by coating. The coating layer increases the transmittance of the LIBS signal of 200nm-500nm and has high reflectivity for the outgoing laser wavelength of 680nm-2000nm.

5. The ultra-wide spectrum three-pulse LIBS detection system for target component detection according to claim 4, characterized in that: For the spectrum-full waveform detection optoelectronic component, where: The first off-axis metal reflector is made of metal aluminum and adopts an aspherical design. It converges the LIBS signal light passing through the plane beam splitter into the first multimode optical fiber, which guides the light into the ICCD spectrometer for LIBS spectral signal analysis. The second off-axis metal reflector is made of metal aluminum and adopts an aspherical design to couple and converge the three-pulse echo laser signal to the second multimode optical fiber, and the second multimode optical fiber is connected to the CT-type grating optical system; The CT grating optical system separates the target scattered laser pulse signal in space according to the spectrum, and the spectrum splitting range is 800nm-1600nm; the one-dimensional fiber array is used to receive the spatial splitting signal, and the fiber array connector is used to connect the one-dimensional fiber array and the high-speed APD array; The high-speed APD array adopts a time-division multiplexing design and is used to detect the echo signal waveform of the laser emitted by the 1064nm laser and the OPO laser. The high-speed APD array consists of multiple fiber APDs and a 1×3 multimode fiber beam splitter. The beam combining end of the 1×3 multimode fiber beam splitter is connected to the fiber APD. The fiber APD bandwidth meets the laser pulse width detection requirements. The lengths of the three splitting fibers at the splitting end differ by a distance of the laser pulse width and are respectively connected to the fiber array end.

6. The ultra-wide spectrum three-pulse LIBS detection system for target component detection according to claim 5, characterized in that: For acquisition and industrial control components, among which: The multi-channel acquisition card has multiple acquisition channels matching the number of fiber APDs, and the bandwidth is not less than the fiber APD bandwidth; The industrial computer is used to obtain data from the spectrometer and acquisition card, analyze the LIBS spectrum signal and target distance information, and the industrial computer is integrated with a laser trigger control module to control the high-energy nanosecond Nd:YAG pulse solid laser and the high-energy wide-spectrum tunable OPO pulse solid laser to work at different delays, and perform secondary enhancement on the LIBS spectrum signal. The industrial computer also feeds back to the electric adjustment mechanism, controls the movement and focusing of the secondary mirror of the receiving telescope based on the multi-spectral measured information, achieves adaptive focusing of the laser spot at the optimal position, and instructs the laser light to calibrate the position of the three-pulse outgoing laser optical axis.

7. An ultra-wide spectrum three-pulse LIBS detection method for target component detection, characterized in that: The method uses the ultra-wide spectrum three-pulse LIBS detection system as described in any one of claims 1 to 6 to realize target component detection.

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