IES87458Y1 - A long pulse libs-raman-lif multi-spectral combined in-situ detection system and its detection method - Google Patents

Abstract

The present invention provides a long pulse LIBS-Raman-LIF multi-spectral joint in-situ detection system, integrating Laser-Induced Breakdown Spectroscopy (LIBS), Raman Spectroscopy (Raman) and Laser Induced Fluorescence (LIF) in a working chamber to realize the simultaneous detection of anions, cations, gas molecules, solid particles and other substances in the combustion field. The all-solid-state long pulse laser is used as the excitation light source and focused on the combustion field through the front optical path. The front optical path has remote zooming function, the generated spectral signal is collected by LIBS spectrometer and Raman-LIF spectrometer through the front optical path. The present invention realizes the combination of key device sharing and multi-spectral technology, and provides a more comprehensive and effective technical means for in-situ detection of high temperature combustion flow field.

Description

A LONG PULSE LIBS-RAMAN-LIF MULTI-SPECTRAL COMBINED IN-SITU DETECTION SYSTEM AND ITS DETECTION METHOD TECHNICAL FIELD id="p-1"

[01] The present invention belongs to the field of aerospace and laser spectroscopy, and specifically relates to a long pulse LIBS—Raman—LIF multi—spectral combined in—situ detection system and its detection method.

BACKGROUND ART id="p-2"

[02] In recent years, China 's aerospace technology is developing continuously, solid rocket motor technology has the advantages of simple structure, high reliability and low cost, which is widely used as the main power device of missile weapons. Therefore, the continuous upgrading of solid motors has also received more and more attention. The primary chamber is one of the core components of the aerospace engine. The reliability and life ofthe engine depend largely on the reliability and effectiveness ofthe combustion chamber. Engine energy conversion is realized by the combustion of solid propellant, but the conversion process is complex, often accompanied by unstable combustion problems.

Wherein, the component information in the combustion process is one of the key parameters that are of great concern to the current engine test. On-line testing the main component concentration ofeombustion field airflow, and the analysis and determination of the content of each component in the gas flow after oxygen supplementation are of great significance for the performance evaluation of solid rocket motors and the improvement of solid propellants. However, the engine combustion process is highly dynamic and has a great disturbance to the surrounding environment. At present, there is still a lack of fast in—situ sensing technology for on—line and non—contact detection of combustion field components. id="p-3"

[03] Laser-Induced Breakdown Spectroscopy (LIBS) technology is to focus the high- power pulsed laser on the surface of the sample by means of an optical system. When the pulsed laser power density on the surface of the sample is large enough to produce plasma, the qualitative analysis ofthe element components and quantitative analysis ofthe content in any physical form of the sample can be realized by collecting the plasma emission spectrum through the optical path system. Compared with the traditional in—situ testing technology, LIBS technology has many advantages such as a simple experimental system, no sample pretreatment, fast analysis speed, and simultaneous detection of multiple elements. It has been widely used in many fields and has broad application prospects in the field, especially in extreme environmental detection. In recent years, LIBS technology has been widely used in flame combustion diagnosis. It is a promising spectral analysis technology in the aerospace field. id="p-4"

[04] Laser Raman Spectroscopy (Raman) technology is a non-destructive molecular spectroscopy technique. The low-energy laser is used to act on the surface of the sample, by receiving the scattering spectrum generated by the material, the scattered light with different frequencies from the incident light is analyzed to obtain the fingerprint information of the molecular vibration and rotational energy levels, which can achieve rapid identification and qualitative detection ofthe corresponding substances. At present, the multi—component measurement of combustion field generally uses spontaneous Raman scattering technology. It can often obtain the Raman signal of the main components of the combustion field by single pulse measurement to complete the quantitative measurement of the main components of the flow field. At present, this technology has been successfully applied to the measurement ofvarious combustion flow field components. id="p-5"

[05] Laser Induced Fluorescence (LIF) technology uses a specific wavelength laser to excite molecules to undergo electronic energy level transitions. When absorbed by the relevant molecules, it will spontaneously emit fluorescence. At present, Lascr Induced Fluorescence technology is commonly used to measure the concentration and temperature of free radicals in the flame field. id="p-6"

[06] The general optical system design is only for one or more specific detection distances. Because when the detection distance changes, the spot size oflaser aggregation, energy density and systemic optical efficiency will change, thereby leading to the collection of plasma spectra with different spectral intensities and characteristics during zoom detection, resulting in different degrees of error in the experimental results. Besides, in high dynamic high temperature combustion field, the combustion field temperature of the engine is up to 3000K. Most current instrumentation cannot withstand such high temperatures, the real conditions of engine combustion field cannot be restored only by theoretical simulation, and analysis results are not available. Therefore, the development of non-contact remote zoom in-situ sensing technology for combustion field detection is an urgent problem to be solved.

SUMMARY id="p-7"

[07] The technical problem to be solved by the present invention is to provide a long pulse LIBS—Raman-LIF multi—spectral combined in-situ detection system and its detection method in view ofthe deficiency ofthe above existing technologies. The system realizes the organic integration of multi—spectral technology. For the choice of excitation light source, LIBS technology often uses high power laser pulses, Raman and LIF technology often use continuous laser. LIBS detection cannot be achieved by continuous laser, while Raman and LIF detection can be realized by pulsed laser. The advantage of using pulsed laser for LIF detection is that it can better suppress the background and perform time-resolved detection of the spectrum. id="p-8"

[08] In order to solve the above technical problems, the technical scheme adopted by the present invention is: a long pulse LIBS-Raman-LIF multi—spectral combined in-situ detection system and its detection method, including a working chamber/ cabin. An all— solid—state long pulse laser, LIBS—Raman—LIF front optical path, LIBS spectrometer, Raman—LIF spectrometer and electronic control system are set up in the working chamber.

The all—solid—statc long pulse laser is the excitation light source. The laser emitted by the all—solid—state long pulse laser is focused on the flame of the combustion flow field after passing through the LIBS-Raman—LIF front optical path. The all—solid—state long pulse laser, LIBS—Raman—LIF front optical path, LIBS spectrometer, Raman—LIF spectrometer are all electrically connected to the electronic control system. LlBS-Raman-LIF front optical path includes a laser beam splitter, LIBS front optical path and Raman-LIF front optical path. The LIBS front optical path and Raman—LIF front optical path share a laser beam splitter. The angle between the laser beam splitter and the incident light is 45 O. The LIBS focus window and Raman—LIF focus window are set at the front of the working cabin. The LIBS focus window is set corresponding to the LIBS front optical path, and the Raman-LIF focus window is set corresponding to the Raman—LIF front optical path. id="p-9"

[09] Preferably, the laser beam splitter is a Nd:YAG laser beam splitter with a projection to reflection ratio of9 : l. id="p-10"

[10] Preferably, the LIBS front optical path includes the first long—wave dichroic mirror, the first concave lens and the first double lens combination. These three combinations are arranged on the right side of the laser beam splitter from left to right along the laser travel direction. The first long—wave dichroic mirror is set in parallel with the laser beam splitter. A broadband reflector is arranged in parallel above the first long— wave-pass dichroic mirror. The first fiber coupling lens is set on the left side of the broadband reflector. The first fiber coupling lens couples the signal light to the fiber and transmits it to the LIBS spectrometer. The cut—offwavelength of the first long wave—pass dichroic mirror is 900 nm. The 1064 nm laser beam through the laser beam splitter passes through the first long-wavc-pass dichroic mirror and the first concave mirror in turn. After passing through the first concave lens and the first double lens combination, the laser is focused into the combustion field. The generated LIBS signal becomes a parallel spectral signal after the first double lens combination and the first concave lens. The first long- wave dichroic mirror is reflected to the broadband reflector, and the signal light is coupled to the fiber by the first fiber coupling lens and transmitted to the LIBS spectrometer, so as to realize the detection of the LIBS signal. id="p-11"

[11] Preferably, the Raman—LIF front optical path includes the second long—wave dichroic mirror, the second concave lens, and the second double lens combination. The second long—wave dichroic mirror is set parallelly below the laser beam splitter. And a frequency doubling crystal is set between the second long-wave dichroic mirror and the laser beam splitter. The second concave lens and the second double lens combination are set in turn on the right of the second long-wave two-way mirror. A long-pass filter and the second fiber coupling lens are arranged in turn on the left side of the second long- wave pass dichroic mirror. The second fiber coupling lens couples the optical signal to the fiber and transmits it to the Raman—LIF spectrometer. The cut—off wavelength of the second long wave—pass dichroic mirror is 535 nm. The 1064 nm laser reflected by the laser beam splitter is converted into 532 nm laser after passing through the frequency— doublcd crystal, through the second long—wave dichroic mirror and the second concave lens in turn, the 532 nm laser is focused into the combustion field after passing through the second concave lens and the second double lens combination. The generated Raman and LIF signals become parallel spectral signals through the second double lens combination and the second concave lens, through the second long-pass dichroic mirror and through the long-pass filter, the second fiber coupling lens is coupled to the fiber and transmitted to the Raman—LIF spectrometer, so as to realize the detection of Raman— LIF signal. id="p-12"

[12] Preferably, the electronic control system includes control module, power supply module and transmission module. The power supply module and transmission module are connected to the control module. id="p-13"

[13] Preferably, the wavelength of the fundamental frequency light emitted by the all— solid—state long pulse laser is 1064 nm. The pulse width ofnanosecond laser is lOOns, and the maximum pulse energy is 250m]. The frequency-doubled crystal is located at the reflection end of the laser beam splitter. The frequency-doubled crystal is used to convert the fundamental frequency light into a laser with a wavelength of532 nm. id="p-14"

[14] Preferably, the diameter of the first concave lens and the second concave lens is inch. The first double lens combination and the second double lens combination are composed of crescent lens and convex lens with the same diameter. The diameter of the first double lens combination and the second double lens combination is 4 inches. id="p-15"

[15] Preferably, the first concave lens and the second concave lens are installed on the first linear motor and the second linear motor respectively. The distance between the concave lens and the double lens combination is adjusted by the linear motor to change the actual focusing distance of the laser, so as to realize the remote zoom function of the combustion field. The moving accuracy of the first linear motor and the second linear motor is 20 L1 m. The first linear motor and the second linear motor are electrically connected to the control module. id="p-16"

[16] Preferably, the LIBS spectrometer has a spectral range of 200-880 nm and a spectral resolution of0.3 nm; the Raman-LIF spectrometer has a spectral range of 0-45 00 cm '1 and a spectral resolution of 10 em'l. LIBS front optical path forms LIBS spectrum, and LIBS spectrum induces atomic and cationic spectra. Raman spectrum and LIF spectrum are formed by Raman-LIF front optical path. Raman spectroscopy provides Raman active anion and molecular spectra. The LIF spectrum provides a molecular spectrum with fluorescent activity. id="p-17"

[17] A long—pulse LIBS—Raman—LIF multi—spectral joint in—situ detection method, includes the following steps: id="p-18"

[18] SI. the all-solid-state long pulse laser is turned on to emit laser pulses, and the laser is focused on the combustion field flame through the LIBS-Raman-LIF front optical path; id="p-19"

[19] S2. the spectral signal is collected by LIBS spectrometer and Raman-LIF spectrometer, LIBS spectrometer (3) adopts external trigger mode, the LIBS spectrometer is triggered by the Q—switched output signal of the all—solid—state long pulse laser, the time interval after laser pulse emission is t1, turning on the LIBS spectrometer, the acquisition time is t2, and then turning off the LIBS spectrometer to obtain the LIBS spectral signal; the Raman—LIF spectrometer adopts the internal trigger mode, after turning on the all— solid—state long pulse laser, turning on the Raman—LIF spectrometer by the control module, the acquisition time is t3, and then turning off the Raman—LIF spectrometer to obtain the Raman—LIF spectral signal. id="p-20"

[20] Preferably, the value oftl is preferably l L1 s, the value of t2 is preferably lms, and the value of t3 is preferably Is; the spectrum acquisition is divided into time and space acquisition modes, wherein, in the time—resolved mode, the combustion field is detected at a fixed point without changing the position of the concave lens, and the time— varying process of the plasma information in the combustion field is obtained; In the spatial resolution mode, the distance between the concave lens and the double lens combination is adjusted by linear motor control, and the plasma radiation information of the combustion field at different spatial positions is analyzed. id="p-21"

[21] Preferably, for the process ofLIBS detection, the plasma induced by pulsed laser has a strong continuous background radiation at the initial stage. This requires setting a certain time delay to avoid the interference ofcontinuous background radiation to obtain discrete characteristic spectral signals. Therefore, a certain time interval t1 is required before the laser pulse and LIBS spectrometer. And the time interval t1 is preferentially set to I 11 s. LIBS spectrum acquisition needs to set a certain acquisition time t2, which can be set I — 50 ms. Since plasma radiation usually lasts for few tens of Li s, the time interval t2 is preferred to 1 ms. Compared to LIBS detection, Raman and LIF detection do not need to set a time delay. The spectrometer is in the internal trigger mode, and the corresponding acquisition time t3 needs to be set. Since the laser used is a pulsed laser, the acquisition of Raman and LIF signals requires a relatively long integration time to improve the detection sensitivity. The acquisition time t3 can be set between 1 and 60 s.

However, the combustion field is in a dynamic process. Integral time should not be too long, time interval t3 preferably set Is. id="p-22"

[22] Compared with the existing technology, the invention has the following advantages: id="p-23"

[23] l. The present invention integrates laser-induced breakdown spectroscopy, laser Raman spectroscopy and laser-induced fluorescence spectroscopy into the same sealed cabin to form a multi-spectral joint detection device. Through the optical path optimization design, the use of the device is reduced, the volume of the device is reduced, and the miniaturization and integration of the device are realized. At the same time, through multi—spectral fusion, comprehensive multi—component spectral information can be provided for combustion field detection, which provides a new technical means for on— linc detection of combustion field components. id="p-24"

[24] 2.The present invention is based on the remote zoom joint detection optical path of the same all-solid-state single pulse laser as the common excitation light source of LIBS, Raman and LIF. And the selected laser pulse width is 100 ns long pulse. It is beneficial to obtain higher intensity spectral signal and improve the detection sensitivity of multispectral technology. The laser with fundamental frequency of 1064 nm is emitted into different optical paths through the laser beam splitter. One of the light paths is converted into a 532 nm laser by a frequency—doubled crystal. Different optical paths complete the excitation and collection of LIBS and Raman—LIF signals respectively, which improves the space utilization of the device. Combined with the structure of Galileo telescope system, the remote and spatial resolution detection of combustion field is realized by the combination of concave lens and double lens, which further improves the practical application ability of multi—spectral combined technology. id="p-25"

[25] 3. The present invention adopts Galileo telescope system to change the actual focusing distance of the laser by adjusting the distance between the lenses, thereby realizing the remote spatial resolution measurement of the combustion field. The present invention adopts a Galileo telescope system structure composed of a concave lens and a double lens. The concave lens is installed on the linear motor displacement platform, and the optical path structure is simulated and analyzed by using the optical path design software. The correlation function between the displacement of the concave lens and the telemetry distance is fitted, and the function is input into the control program. The controller adjusts the moving distance of the linear motor to complete the remote spatial resolution measurement of the combustion field. id="p-26"

[26] 4. At present, most of the commonly used pulse lasers are short pulses with a pulse width of about 10 ns, resulting in low LIBS detection sensitivity. The present invention uses a long pulse laser with a pulse width of 100 ns, which can effectively increase the interaction time between the laser and the plasma and improve the LIBS detection sensitivity. But for Raman and LIF spectra, based on the pulse laser, the long pulse laser is also beneficial to enhance the Raman and LIF spectra. At the same time; the present invention adopts multi—spectral fusion method, wherein, LIBS spectral excitation induces the generation of atomic and cationic spectra, Raman spectrum excitation produces Raman active anions and molecular spectra, LIF spectra provide molecular spectra with fluorescent activity. The three spectra are integrated with each other and complement each other, providing multi—component and multi-spectral information for combustion field detection and diagnosis. id="p-27"

[27] The following is a further detailed description of the invention in combination with drawings and implementation examples.

BRIEF DESCRIPTION OF THE DRAWINGS id="p-28"

[28] FIG. 1 is the overall structure diagram of the present invention. id="p-29"

[29] FIG. 2 is the structure diagram of LlBS-Raman-LIF front optical path in the present invention. id="p-30"

[30] Label description of drawings: id="p-31"

[31] l: all—solid—state long pulse laser; 2: LIBS—Raman—LIF front optical path; id="p-32"

[32] 2—1: LIBS front optical path; id="p-33"

[33] 2-2: Raman-LIF front optical path; 3: LIBS spectrograph; 4: Raman-LIF spectrometer; id="p-34"

[34] 5: electronic control system; 6: laser beam splitter; id="p-35"

[35] 7: the first long-wave dichroic mirror; id="p-36"

[36] 8: the first concave lens; 9: the first linear motor; id="p-37"

[37] 10: the first double lens combination; id="p-38"

[38] ll: broadband reflector; 12: the first fiber coupling lens; id="p-39"

[39] 13: frequency—doubled crystal; id="p-40"

[40] 14: the second long—wave dichroic mirror; 15: the second concave lens; [4]] 16: the second linear motor; id="p-42"

[42] 17: the second double lens combination; 18: long—pass filter; id="p-43"

[43] 19: the second fiber coupling lens; id="p-44"

[44] 20: working space; 21-1: LIBS focus window; 21—2: Raman-LIF focus window.

DETAILED DESCRIPTION OF THE EMBODIMENTS id="p-45"

[45] As shown in FIGS 1 and 2, the present invention includes a working chamber.

All—solid—state long pulse laser 1, LIBS—Raman—LIF front optical path 2, LIBS spectrometer 3, Raman—LIF spectrometer 4 and electronic control system 5 are set in the working cabin. All—solid—state long pulse laser 1 is the excitation light source. The laser emitted by the all-solid—state long pulse laser 1 is focused on the combustion flow field flame after passing through the LIBS-Raman—LIF front optical path 2.A11—solid—state long pulse laser 1, LIBS-Raman-LIF front optical path 2, LIBS spectrometer 3, Raman-LIF spectrometer 4 are all electrically connected to the electronic control system 5. LIBS— Raman—LIF front optical path 2 includes laser beam splitter 6, LIBS front optical path 2— land Raman-LIF front optical path 2-2. LIBS front optical path 2—1 and Raman-LIF front optical path 2—2 share a laser beam splitter 6. The angle between the laser beam splitter and the incident light is 450. LIBS focus window 21 —1 and Raman—LIF focus window 21— are set at the front of the working cabin 20. The LIBS focus window 21—1 is set corresponding to the LIBS front optical path 2—1, and the Raman—LIF focus window 21— is set corresponding to the Raman—LIF front optical path 2—2. id="p-46"

[46] In this example, the laser beam splitter is a Nd: YAG laser beam splitter with a projection to reflection ratio of9 : 1. id="p-47"

[47] In this example, LIBS front optical path 2—1 includes the first long—wave diehroic mirror 7, the first concave lens 8 and the first double lens combination 10. These three combinations are arranged on the right side of the laser beam splitter 6 from left to right along the laser travel direction. The first long-wave diehroic mirror 7 is set in parallel with the laser beam splitter 6. A broadband reflector 11 is arranged in parallel above the first long-wave-pass diehroic mirror 7. The first fiber coupling lens 12 is set on the left side of the broadband reflector 11. The first fiber coupling lens 12 couples the signal light to the fiber and transmits it to the LIBS spectrometer 3. The cut-off wavelength of the first long wave-pass diehroic mirror 7 is 900 nm. The 1064 nm laser beam through the laser beam splitter 6 passes through the first long—wave—pass diehroic mirror 7 and the first concave lens 8 in turn. After through the first concave lens 8 and the first double lens combination 10, the laser is focused into the combustion field. The generated LIBS signal becomes a parallel spectral signal after the first double lens combination 10 and the first concave lens 8. The first long-wave diehroic mirror 7 is reflected to the broadband reflector 11, and the signal light is coupled to the fiber by the first fiber coupling lens 12 and transmitted to the LIBS spectrometer 3, so as to realize the detection of LIBS signal. id="p-48"

[48] In this example, the Raman-LIF front optical path 2-2 includes the second long- wave diehroic mirror 14, the second concave lens 15, and the second double lens combination 17. The second long—wave diehroic mirror 14 is set parallelly below the laser beam splitter 6. And a frequency—doubling crystal 13 is set between the second long—wave diehroic mirror 14 and the laser beam splitter 6. The second concave lens 15 and the second double lens combination 17 are set in turn on the right of the second long—wave two—way mirror 14. A long—pass filter 18 and the second fiber coupling lens 19 are arranged in turn on the left side of the second long—wave pass diehroic mirror 14. The second fiber coupling lens 19 couples the optical signal to the fiber and transmits it to the Raman—LIF spectrometer 4. The cut-off wavelength of the second long wave-pass diehroic mirror 14 is 535 nm. The 1064 nm laser reflected by the laser beam splitter 6 is converted into 532 nm laser after passing through frequency—doubled crystal 13, through the second long—wave diehroic mirror 14 and the second concave lens 15 in tum, the 532 nm laser is focused into the combustion field after passing through the second concave lens 15 and the second double lens combination 17. The generated Raman and LIF signals become parallel spectral signals through the second double lens combination 17 and the second concave lens 15, through the second long—pass dichroic mirror 14 and through the long-pass filter 18, the second fiber coupling lens 19 is coupled to the fiber and transmitted to the Raman-LIF spectrometer 4, so as to realize the detection of Raman-LIF signal. id="p-49"

[49] In this example, the electronic control system 5 includes control module, power supply module and transmission module. The power supply module and transmission module are connected to the control module. id="p-50"

[50] In this example, the wavelength of the fundamental frequency light emitted by the all—solid—state long pulse laser is 1064 nm. The pulse width of nanosecond laser is lOOns, and the maximum pulse energy is 250m]. The frequency—doubled crystal is located at the reflection end of the laser beam splitter. The frequency-doubled crystal is used to convert the fundamental frequency light into a laser with a wavelength of 532 nm. id="p-51"

[51] In this example, the diameter of the first concave lens 8 and the second concave lens 15 is 1 inch. The first double lens combination 10 and the second double lens combination 17 are composed of crescent lens and convex lens with the same diameter.

The diameter of the first double lens combination 10 and the second double lens combination 17 is 4 inches. id="p-52"

[52] In this example, the first concave lens 8 and the second concave lens 15 are installed on the first linear motor 9 and the second linear motor 16 respectively. The distance between the concave lens and the double lens combination is adjusted by the linear motor to change the actual focusing distance of the laser, so as to realize the remote zoom function of the combustion field. The moving accuracy of the first linear motor 9 and the second linear motor 16 is 20 Ll m. The first linear motor 9 and the second linear motor 16 are electrically connected to the control module. id="p-53"

[53] In this example, the LIBS spectrometer 3 has a spectral range of200-880 nm and a spectral resolution of 0.3 nm; the Raman-LIF spectrometer 4 has a spectral range of 0- cm '1 and a spectral resolution of 10 em'l. LIBS front optical path 2-1 forms LIBS spectrum, and LIBS spectrum induces atomic and cationic spectra. Raman spectrum and LIF spectrum are formed by Raman-LIF front optical path. Raman spectroscopy provides Raman active anion and molecular spectra. The LIF spectrum provides a molecular spectrum with fluorescent activity. id="p-54"

[54] When the device system is used, the following steps are included: id="p-55"

[55] 81. the all—solid—statc long pulse laser is turned on to emit laser pulses, and the laser is focused on the combustion field flame through the LIBS—Raman—LIF front optical path; id="p-56"

[56] 32. the spectral signal is collected by LIBS spectrometer (3) and Raman—LIF spectrometer (4), LIBS spectrometer (3) adopts external trigger mode, the LIBS spectrometer (3) is triggered by the Q-switched output signal of the all-solid—state long pulse laser (1), the time interval after laser pulse emission is t1, turning on the LIBS spectrometer (3), the acquisition time is t2, and then turning off the LIBS spectrometer (3) to obtain the LIBS spectral signal; the Raman—LIF spectrometer (4) adopts the internal trigger mode, after turning on the all—solid—state long pulse laser (1), turning on the Raman—LIF spectrometer (4) by the control module, the acquisition time is t3, and then turning off the Raman-LIF spectrometer (4) to obtain the Raman—LIF spectral signal. id="p-57"

[57] Wherein, the value oftl is preferably 1 Ll s, the value of t2 is preferably lms, and the value of t3 is preferably Is; the spectrum acquisition is divided into time and space acquisition modes, wherein, in the time—resolved mode, the combustion field is detected at a fixed point without changing the position of the concave lens, and the time—varying process of the plasma information in the combustion field is obtained; In the spatial resolution mode, the distance between the concave lens and the double lens combination is adjusted by linear motor control, and the plasma radiation information of the combustion field at different spatial positions is analyzed. id="p-58"

[58] Wherein, for the process of LIBS detection, the plasma induced by pulsed laser has strong continuous background radiation at the initial stage. This requires setting a certain time delay to avoid the interference of continuous background radiation to obtain discrete characteristic spectral signals. Therefore, a certain time interval t1 is required before the laser pulse and LIBS spectrometer. And the time interval t1 is preferentially set to 1 L1 s. LIBS spectrum acquisition needs to set a certain acquisition time t2, which can be set 1 ~50 ms. Since plasma radiation usually lasts for few tens of 11 s, the time interval t2 is preferred to 1 ms. Compared to LIBS detection, Raman and LIF detection do not need to set time delay. The spectrometer is in the internal trigger mode, and the corresponding acquisition time t3 needs to be set. Since the laser used is a pulsed laser, the acquisition of Raman and LIF signals requires a relatively long integration time to improve the detection sensitivity. The acquisition time t3 can be set between 1 and 60 s.

However, the combustion field is in a dynamic process. Integral time should not be too long, time interval t3 is preferably set to Is. id="p-59"

[59] The above is only a better embodiment of the invention and does not impose any restriction on the invention. Any simple modification, change and equivalent change made to the above implementation eases according to the essence of the invention technology are still within the protection scope of the technical scheme of the invention.

Claims (5)

1. A long pulse LIBS-Raman—LIF multi—spectral combined in—situ detection system, including a working chamber; all-solid-state long pulse laser 1, LlBS—Raman-LIF front optical path 2, LIBS spectrometer 3, Raman-LIF spectrometer 4 and electronic control system 5 are set in the working chamber; the all—solid—state long pulse laser 1 is the excitation light source, the laser emitted by the all—solid—state long pulse laser 1 is focused on the combustion flow field flame after passing through the LIBS—Raman—LIF front optical path 2; the all—solid—statc long pulse laser 1, LlBS—Raman—LIF front optical path 2, LIBS spectrometer 3, the Raman—LIF spectrometer 4 are all electrically connected to the electronic control system 5; the LIB S—Raman—LIF front optical path 2 includes a laser beam splitter 6; LIBS front optical path 2—1 and Raman—LIF front optical path 2-2 share the laser beam splitter 6; the angle between the laser beam splitter and the incident light is 45"; LIBS focus window 21-1 and Raman—LIF focus window 21—2 are set at the fron of the working chamber 20; the LIBS focus window 21—1 is set corresponding to the LIBS front optical path 2—], and the Raman—LIF focus window 21—2 is set corresponding to thc Raman-LIF front optical path 2-2.

2. The long pulse LIBS-Raman-LIF multi-spectral combined in-situ detection system according to claim 1, wherein the LIBS front optical path 2-1 includes a first long- wave dichroic mirror 7, a first concave lens 8 and a first double lens combination 10; these three combinations are arranged on the right side of the laser beam splitter 6 from left to right along the laser travel direction; the first long-wave dichroic mirror 7 is set in parallel with the laser beam splitter 6; a broadband reflector 11 is arranged in parallel above the first long—wave—pass dichroic mirror 7; a first fiber coupling lens 12 is set on the left side of the broadband reflector 11; the first fiber coupling lens 12 couples the signal light to the fiber and transmits it to the LIBS spectrometer 3; the cut—off wavelength of the first long wave-pass dichroic mirror 7 is 900 nm.

3. The long pulse LIBS-Raman-LIF multi-spectral combined in-situ detection system according to claim 2, wherein the Raman-LIF front optical path 2-2 includes a second long-wave dichroic mirror 14, a second concave lens 15, and a second double lens combination 17; the second long-wave dichroic mirror 14 is set parallelly below the laser beam splitter 6, and a frequency—doubling crystal 13 is set between the second long—wave dichroic mirror 14 and the laser beam splitter 6; the second concave lens 15 and the second double lens combination 17 are set in turn on the right of the second long—wave two—way mirror 14; a long-pass filter 18 and a second fiber coupling lens 19 are arranged in turn on the left side ofthe second long—wave pass dichroic mirror 14; the second fiber coupling lens 19 couples the optical signal to the fiber and transmits it to the Raman—LIF spectrometer 4; the cut—off wavelength of the second long wave—pass dichroic mirror 14 is 535 nm.

4. The long pulse LlBS-Raman-LIF multi—spectral combined in—situ detection system according to claim 1, wherein the electronic control system 5 includes a control module, a power supply module and a transmission module; the power supply module and the transmission module are connected to the control module.

5. A method for LIBS—Raman—LIF multi—spcctral joint in—situ detection for