CN-121830516-B - Space filtering type differential resonance photoacoustic stimulated Raman detection system and method

CN121830516BCN 121830516 BCN121830516 BCN 121830516BCN-121830516-B

Abstract

The invention discloses a space filtering type differential resonance photoacoustic stimulated Raman detection system and a method, which belong to the technical field of gas detection, wherein the system comprises a laser source module, a Raman frequency shifter module, a space filtering type differential resonance photoacoustic cell and a signal acquisition and processing unit; the high-energy pulse laser generated by the laser source module is collimated and then is emitted into the Raman frequency shifter module, the bicolor coherent beam output by the Raman frequency shifter module is focused by the achromatic lens and then coaxially emitted into the center of the space filtering type differential resonance photoacoustic cell, the excited photoacoustic signal is collected by two microphones of the space filtering type differential resonance photoacoustic cell, the signal collecting and processing unit is electrically connected with each microphone, two acoustic tubes of the space filtering type differential resonance photoacoustic cell are symmetrically arranged in a large tube buffer cavity, and two Brewster windows are respectively and hermetically arranged at two ends of the large tube buffer cavity. The invention can effectively inhibit the optical damage of the window sheet and improve the system stability.

Inventors

LI ZHENGANG
YU XIN
XU HAICHUN
MIAO JUNFANG
WANG CANLONG
FANG YONGQING
LIU JIAXIANG
PAN YING
FANG YONGHUA

Assignees

中国科学院合肥物质科学研究院

Dates

Publication Date: 20260512
Application Date: 20260311

Claims (10)

1. A space filtering type differential resonance photoacoustic stimulated Raman detection system is characterized by comprising a laser source module, a Raman frequency shifter module, a space filtering type differential resonance photoacoustic cell and a signal acquisition and processing unit, wherein high-energy pulse laser generated by the laser source module is collimated and then is emitted into the Raman frequency shifter module, a bicolor coherent beam output by the Raman frequency shifter module is focused by an achromatic lens and then coaxially emitted into the radial tube center of the space filtering type differential resonance photoacoustic cell, and an excited photoacoustic signal is acquired by two microphones of the space filtering type differential resonance photoacoustic cell; The space filtering type differential resonance photoacoustic cell comprises a first acoustic pipe, a second acoustic pipe, a large pipe buffer cavity, a first Brewster window, a second Brewster window, a first microphone, a second microphone and an optical trap, wherein the first acoustic pipe and the second acoustic pipe are symmetrically arranged in the large pipe buffer cavity, the first Brewster window and the second Brewster window are respectively and hermetically arranged at two ends of the large pipe buffer cavity, the optical trap is arranged at the tail end of an optical path at one side of an optical outlet of the space filtering type differential resonance photoacoustic cell, and the first microphone and the second microphone are respectively and hermetically arranged at the axial middle parts of the first acoustic pipe and the second acoustic pipe.
2. The space filtering type differential resonance photoacoustic stimulated raman detection system of claim 1, wherein the laser source module comprises a laser, a laser beam emitted by the laser enters the raman frequency shifter module through an optical window, and the laser adopts a neodymium-doped yttrium aluminum garnet solid laser.
3. The spatially filtered differential resonance photoacoustic stimulated raman detection system of claim 2 wherein the raman shifter module comprises a raman shifter, a pressure valve disposed in the raman shifter, an optical window sealingly mounted to the raman shifter light inlet and a long Jiao Pingtu lens sealingly mounted to the raman shifter light outlet.
4. The space filtering type differential resonance photoacoustic stimulated Raman detection system of claim 1, wherein the signal acquisition and processing unit comprises a differential circuit, a preamplifier, a band-pass filter, a data acquisition card and an upper computer, wherein the input end of the differential circuit is respectively connected with a first microphone and a second microphone, the output end of the differential circuit is sequentially connected with the preamplifier, the band-pass filter and the data acquisition card, the data acquisition card is in communication connection with the upper computer, the differential circuit performs differential processing on photoacoustic signals of a first acoustic tube and a second acoustic tube, the preamplifier amplifies the photoacoustic signals after differential processing, and the band-pass filter primarily filters low-frequency noise in the environment, the data acquisition card acquires time domain signals, and the upper computer performs spectrum analysis on the time domain photoacoustic signals and performs inversion after extracting characteristic spectrums to obtain the concentration of target gas to be detected.
5. The spatially filtered differential resonance photoacoustic stimulated raman detection system of claim 3 wherein the optical window is sealed with a fused quartz window and the output is sealed with a long Jiao Pingtu lens while collimating the diverging beam, the surface of the raman shifter being provided with air holes through which the raman shifter is first evacuated and then Gao Chunla man-active gas is pressed in.
6. The spatially filtered differential resonance photoacoustic stimulated raman detection system of claim 1 wherein the centers of the first acoustic tube and the second acoustic tube are each provided with an aperture, and the first acoustic signal extraction tube and the second acoustic signal extraction tube are each sealingly connected between the apertures and the microphones to guide photoacoustic signals to the first microphone and the second microphone.
7. The spatially filtered differential resonance photoacoustic stimulated raman detection system of claim 1 wherein the acromatic lens acts as a beam-combining focusing lens, the surface of which is coated with a visible light anti-reflection film.
8. The space filtering type differential resonance optoacoustic stimulated Raman detection system is characterized in that two ends of a large tube buffer cavity are processed into Brewster angle inclined planes conforming to the refractive index relation by adopting a precise chamfering processing technology, a first Brewster window and a second Brewster window are respectively embedded into annular positioning counter bores on the inclined planes at two ends of the large tube buffer cavity, and an air inlet hole and an air outlet hole are respectively arranged at two ends of the large tube buffer cavity.
9. A spatially filtered differential resonance photoacoustic stimulated raman detection system according to claim 3, wherein the raman frequency shifter is made of stainless steel material.
10. A spatially filtered differential resonance photoacoustic stimulated raman detection method for a spatially filtered differential resonance photoacoustic stimulated raman detection system according to any one of claims 1 to 9, comprising: s1, preheating a laser, and setting working parameters of the laser through an upper computer; s2, monitoring and adjusting the pressure of Gao Chunla Mans active gas in the Raman frequency shifter, generating stimulated Raman scattering of pump light output by the laser in the cavity to generate first-order Stokes light, scanning different pressures, measuring the product of residual pump light and the first-order Stokes light energy, taking the pressure corresponding to the maximum value as the optimal experimental pressure, and fixing to obtain the optimal bicolor coherent light source; S3, determining the longitudinal resonant modal frequency of the spatial filtering type differential resonant photoacoustic cell; S4, exhausting air in the large pipe buffer cavity, the first acoustic pipe and the second acoustic pipe, and pressing the air into a gas sample to be detected through an air inlet; S5, focusing the bicolor coherent light beams output by the Raman frequency shifter through an achromatic lens, and converging the bicolor coherent light beams at the geometric center of the first acoustic tube; s6, the first microphone and the second microphone respectively collect photoacoustic signals in the first acoustic pipe and the second acoustic pipe, and the two photoacoustic signals enter a differential circuit to perform inverse summation operation at the same time, so that pure differential mode photoacoustic signals are output; S7, the differential-mode photoacoustic signal sequentially passes through a preamplifier and a band-pass filter and is acquired by a data acquisition card to obtain a time-domain photoacoustic signal; S8, the upper computer receives the time domain photoacoustic signal, converts the time domain photoacoustic signal into a frequency domain signal, and extracts a signal amplitude at a resonance frequency to serve as an effective photoacoustic signal value corresponding to the target gas to be detected; s9, sequentially preparing and measuring a plurality of groups of gas samples to be measured with different standard concentrations according to S4 to S8, and performing linear fitting on the concentration of the target gas to be measured and the effective photoacoustic signal amplitude to obtain a system calibration curve; S10, substituting the time domain photoacoustic signal into the system calibration curve of S9 for the gas sample to be detected with unknown concentration, and inverting the concentration of the gas sample to be detected.

Description

Space filtering type differential resonance photoacoustic stimulated Raman detection system and method Technical Field The invention belongs to the technical field of gas detection, and particularly relates to a space filtering type differential resonance photoacoustic stimulated Raman detection system and method. Background As an indirect absorption spectrum technology, the photoacoustic spectrum technology has the advantages of high sensitivity, good selectivity, quick response, zero background detection and the like, and is widely applied to the field of trace gas detection. However, the gas analysis technology based on the infrared absorption principle has the fundamental limitation that the hydrogen equivalent nuclear diatomic molecule cannot be detected because of the dependence of the change of the molecular dipole moment. Raman spectroscopy techniques, while capable of fingerprint identification of nonpolar molecules, have extremely weak spontaneous raman scattering signals. Although the traditional stimulated Raman scattering technology can identify hydrogen, the detection essence is that weak light intensity change signals are extracted under strong background laser, so that the detection sensitivity and stability of low-concentration gas are greatly limited. The existing photoacoustic stimulated raman technique (Photoacoustic Raman Spectroscopy, PARS) combines the molecular selectivity of stimulated raman transition and the 'zero background' detection advantage of photoacoustic spectroscopy, and realizes high signal-to-noise ratio measurement by detecting an acoustic wave signal generated by the non-radiative relaxation of molecules to release heat energy. In homonuclear diatomic gas (e.g., H 2、N2、O2) detection, photoacoustic stimulated Raman techniques typically require very high power pulsed lasers to induce nonlinear optical effects. But high power pulsed lasers, when passing through photoacoustic cell panes, can cause two core technical problems: the window sheet damage risk is that the traditional window sheet which is vertically installed or not installed at the Brewster angle is extremely easy to cause optical damage due to energy absorption or surface reflection when bearing Nd-YAG (neodymium-doped yttrium aluminum garnet) high-energy pulse laser with the order of tens of millijoules. The thermal noise floor, the unavoidable weak absorption of the window panes, can lead to local temperature rise and the generation of pressure waves. The window noise can be directly diffused into the resonant cavity to form background noise which cannot be completely eliminated by an electrical means, so that an effective signal generated by trace gas is extremely submerged, and the breakthrough of a system to the ppb (parts per billion) level detection limit is severely limited. Disclosure of Invention In order to solve the technical problems, the invention adopts the following technical scheme: A space filtering type differential resonance photoacoustic stimulated Raman detection system comprises a laser source module, a Raman frequency shifter module, a space filtering type differential resonance photoacoustic cell and a signal acquisition and processing unit, wherein high-energy pulse laser generated by the laser source module is collimated and then is emitted into the Raman frequency shifter module, a bicolor coherent beam output by the Raman frequency shifter module is focused by an achromatic lens and then coaxially emitted into the radial tube center of the space filtering type differential resonance photoacoustic cell, and an excited photoacoustic signal is acquired by two microphones of the space filtering type differential resonance photoacoustic cell; The space filtering type differential resonance photoacoustic cell comprises a first acoustic pipe, a second acoustic pipe, a large pipe buffer cavity, a first Brewster window, a second Brewster window, a first microphone, a second microphone and an optical trap, wherein the first acoustic pipe and the second acoustic pipe are symmetrically arranged in the large pipe buffer cavity, the first Brewster window and the second Brewster window are respectively and hermetically arranged at two ends of the large pipe buffer cavity, the optical trap is arranged at the tail end of an optical path at one side of an optical outlet of the space filtering type differential resonance photoacoustic cell, and the first microphone and the second microphone are respectively and hermetically arranged at the axial middle parts of the first acoustic pipe and the second acoustic pipe. A space filtering type differential resonance photoacoustic stimulated Raman detection method comprises the following steps: s1, preheating a laser, and setting working parameters of the laser through an upper computer; s2, monitoring and adjusting the pressure of Gao Chunla Mans active gas in the Raman frequency shifter, generating stimulated Raman scattering of pump light output by the l