CN-121978020-A - Compact low-frequency resonance photoacoustic Raman detection system and method based on hollow fiber enhancement

CN121978020ACN 121978020 ACN121978020 ACN 121978020ACN-121978020-A

Abstract

The invention discloses a compact low-frequency resonance photoacoustic Raman detection system and a compact low-frequency resonance photoacoustic Raman detection method based on hollow fiber enhancement, and belongs to the technical field of gas detection, wherein in the system, low-energy high-frequency pulse laser generated by a high-repetition-frequency low-energy laser source module is focused by a convex lens and is emitted into a hollow fiber Raman frequency shifter module; after being collimated by an achromatic collimating lens, the bicolor coherent light beam output by the hollow fiber Raman frequency shifter module coaxially enters the spiral connection pipe type low-frequency resonance photoacoustic cell, the excited resonance photoacoustic signal is collected by a first microphone arranged in a signal cavity of the spiral connection pipe type low-frequency resonance photoacoustic cell and a second microphone arranged in a reference cavity, and the signal collection and processing unit is electrically connected with the first microphone and the second microphone and is used for carrying out differential phase locking processing and concentration inversion on the collected resonance photoacoustic signal to obtain a concentration value of gas to be measured. The invention realizes the accurate locking of the laser repetition frequency and the acoustic resonance frequency and the high Q value resonance amplification of the photoacoustic signal.

Inventors

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

Assignees

中国科学院合肥物质科学研究院

Dates

Publication Date: 20260505
Application Date: 20260312

Claims (10)

1. The compact low-frequency resonance photoacoustic Raman detection system based on hollow fiber reinforcement is characterized by comprising a high-repetition-frequency low-energy laser source module, a hollow fiber Raman frequency shifter module, a spiral connection tube type low-frequency resonance photoacoustic cell and a signal acquisition and processing unit, wherein the high-repetition-frequency low-energy laser source module, the hollow fiber Raman frequency shifter module, the spiral connection tube type low-frequency resonance photoacoustic cell and the signal acquisition and processing unit are sequentially arranged along an optical path; The device comprises a high-repetition frequency low-energy laser source module, a hollow fiber Raman frequency shifter module, a signal acquisition and processing unit, a differential phase locking processing and concentration inversion unit, a signal acquisition and processing unit and a concentration value acquisition unit, wherein low-energy high-frequency pulse laser generated by the high-repetition frequency low-energy laser source module is focused by a convex lens and is emitted into the hollow fiber Raman frequency shifter module, a bicolor coherent beam output by the hollow fiber Raman frequency shifter module is collimated by an achromatic collimating lens and then coaxially emitted into a spiral connection pipe type low-frequency resonance photoacoustic cell, the excited resonance photoacoustic signal is acquired by a first microphone arranged in a signal cavity of the spiral connection pipe type low-frequency resonance photoacoustic cell and a second microphone arranged in a reference cavity, and the signal acquisition and processing unit is electrically connected with the first microphone and the second microphone and is used for carrying out differential phase locking processing and concentration inversion on the acquired resonance photoacoustic signal to obtain the concentration value of gas to be detected.
2. The compact low-frequency resonant photoacoustic raman detection system based on hollow-core optical fiber enhancement according to claim 1, wherein a pulse laser is used as a pumping source in the high-repetition-frequency low-energy laser source module.
3. The compact low-frequency resonant photoacoustic raman detection system of claim 1, wherein the hollow fiber raman shifter module comprises a hollow fiber, a first air chamber and a second air chamber respectively installed at two ends of the hollow fiber, a first optical window and a second optical window respectively installed on the light transmitting end surfaces of the first air chamber and the second air chamber in a sealing manner, a convex lens arranged at an incident end and an achromatic collimating lens arranged at an emergent end; The first air chamber and the second air chamber are miniature high-pressure air chambers used for sealing hollow optical fibers and filling Raman active gas, the first optical window and the second optical window are used for transmitting light and maintaining high-pressure sealing of the first air chamber and the second air chamber, the convex lens is used for matching laser mode fields and coupling the laser mode fields into the hollow optical fibers through the first optical window, and the achromatic collimating lens is used for collimating divergent light beams output through the second optical window.
4. A compact low frequency resonant photoacoustic raman detection system based on hollow fiber reinforcement according to claim 3, wherein the first air chamber is provided with a first air valve for inflation and deflation and a pressure valve for monitoring air pressure, and the second air chamber is provided with a second air valve for inflation and deflation.
5. The compact low-frequency resonant photoacoustic raman detection system based on hollow fiber reinforcement according to claim 1, wherein the spiral-link tube type low-frequency resonant photoacoustic cell comprises a signal cavity, a reference cavity, a spiral-link tube or labyrinth folded structure, an optical trap; the signal cavity and the reference cavity are placed in parallel and are communicated through a spiral connecting pipe or a labyrinth folding structure to form a differential Helmholtz resonance structure, the double-color coherent light beam collimated by the achromatic collimating lens only passes through the signal cavity, no light passes through the reference cavity, and the optical trap is arranged at the tail end of a light path at one side of a light outlet of the signal cavity and is used for absorbing a transmitted light beam emitted from a third Brewster window.
6. The compact low-frequency resonance photoacoustic Raman detection system based on hollow fiber reinforcement according to claim 5, wherein a first Brewster window and a third Brewster window are respectively arranged at two ends of a signal cavity of the spiral connection tube type low-frequency resonance photoacoustic cell, a second Brewster window and a fourth Brewster window are respectively arranged at two ends of a reference cavity and are sealed by sealing rings, and a bicolor coherent light beam collimated by the achromatic collimating lens is injected through the first Brewster window and is emitted from the third Brewster window.
7. The compact low frequency resonant photoacoustic raman detection system of claim 5, wherein the signal chamber and the reference chamber are each configured with a fourth gas valve and a third gas valve for the ingress and egress of a gas to be detected.
8. The compact low-frequency resonance photoacoustic Raman detection system based on hollow fiber reinforcement according to claim 5, wherein the signal acquisition and processing unit comprises a first microphone arranged in the signal cavity, a second microphone arranged in the reference cavity, a differential module, a filter amplification module, a phase-locked amplifier, a data acquisition card and an upper computer, wherein the first microphone and the second microphone are respectively connected to the input end of the differential module, and the differential module, the filter amplification module, the phase-locked amplifier, the data acquisition card and the upper computer are sequentially connected.
9. The compact low frequency resonant photoacoustic raman detection system of claim 5 based on hollow fiber reinforcement wherein the signal and reference cavities are cylindrical cavities of the same shape and size and placed in parallel.
10. A compact low frequency resonant photoacoustic raman detection method based on hollow fiber reinforcement for a compact low frequency resonant photoacoustic raman detection system based on hollow fiber reinforcement as recited in any one of claims 1 to 9, comprising: Step 1, starting up a compact low-frequency resonance photoacoustic Raman detection system based on hollow fiber reinforcement, and electrifying to preheat a pulse laser; Step2, the low-energy high-frequency pulse laser output by the pulse laser is focused by a convex lens and enters a coiled hollow fiber, under the limit of a hollow fiber waveguide, the laser pulse and high-pressure hydrogen are subjected to high-efficiency stimulated Raman scattering in the hollow fiber to generate first-order Stokes light, and the hollow fiber outputs a bicolor coherent light beam containing the pump light and the first-order Stokes light; Step 3, the dual-color coherent light beam output from the hollow fiber passes through a signal cavity of the spiral connection pipe type low-frequency resonant photoacoustic cell after being collimated, the repetition frequency of the pulse laser is completely consistent with the inherent resonance frequency of the spiral connection pipe type low-frequency resonant photoacoustic cell, a periodic thermal wave generated by absorption of light energy by gas molecules to be tested drives a sound field to perform forced vibration, the sound wave generates constructive interference in the whole resonant structure formed by the signal cavity and a reference cavity, and the amplitude of the excited resonant photoacoustic signal is accumulated and amplified by Q times along with the time; Step 4, synchronously acquiring resonance photoacoustic signals in the signal cavity and the reference cavity by a first microphone arranged in the signal cavity and a second microphone arranged in the reference cavity, removing most of environment common mode noise after the two paths of signals are processed by a difference module, then enabling the signals to enter a lock-in amplifier, and carrying out phase-sensitive detection on the signals after difference by using the synchronous signals of a pulse laser as a reference to extract the resonance photoacoustic signal amplitude with extremely high signal-to-noise ratio; And 5, the upper computer inverts the concentration value of the gas to be detected according to the resonance photoacoustic signal amplitude value measured in the step 4 and combining a pre-calibrated gas concentration-resonance photoacoustic signal amplitude calibration curve.

Description

Compact low-frequency resonance photoacoustic Raman detection system and method based on hollow fiber enhancement Technical Field The invention belongs to the technical field of gas detection, and particularly relates to a compact low-frequency resonance photoacoustic Raman detection system and method based on hollow fiber reinforcement. Background The photoacoustic stimulated Raman spectroscopy (PARS) has important roles in the fields of energy safety, environmental monitoring and the like because of the capability of detecting diatomic molecules (such as hydrogen and nitrogen) without infrared absorption activity and the zero background detection advantage. However, in the progress of the prior art towards portability and refinement, two pairs of core physical mechanisms of optical gain and device damage, acoustic resonance and physical size are in conflict, and serious problems of low time domain energy utilization exist, and the following two aspects are particularly shown: (1) Contradiction between raman frequency shifter volume and fiber damage threshold conventional raman frequency shifters typically use stainless steel straight tubes up to 1 meter or more to encapsulate high pressure gas (> 10 atm) in order to obtain sufficient stimulated raman gain, resulting in a bulky system. The advent of hollow core optical fibers (HCF) has provided the possibility for miniaturization, which can confine the optical field within the micron-sized core, greatly improving the raman gain coefficient. But the optical damage threshold of HCF is much lower than that of free space optics. Conventional PARS systems typically employ high energy (50-100 mJ), low repetition rate (10 Hz) pulsed lasers in order to pursue a single pulse high signal-to-noise ratio. Such high energy pulses, once coupled into hollow core fibers, are very prone to burn out the fiber end face or damage the cladding microstructure, resulting in device failure. (2) Mismatch of laser repetition frequency and photoacoustic cell resonance frequency problems in order to maintain a compact volume, the geometry of conventional photoacoustic cells (e.g., cylindrical or H-shaped) is small, with first order longitudinal resonance frequencies typically in the range of 1000Hz-2000Hz or even higher, depending on acoustic theory. A commonly used high energy Nd: YAG (neodymium doped yttrium aluminum garnet) laser operates at a low repetition rate of 10 Hz. When a 10Hz laser pulse excites a 1000Hz photoacoustic cell, it is equivalent to pushing the system every 100 cycles of acoustic oscillation. During the time interval between two laser pulses (100 ms), the acoustic oscillations in the photoacoustic cell have been depleted by damping. This means that existing systems are actually performing discrete pulse damped oscillation detection, rather than continuous steady state resonance detection. The high Q value (quality factor) of the photoacoustic cell is difficult to exert an energy storage effect, and a resonance effect cannot be utilized to accumulate and amplify signals, resulting in extremely low utilization efficiency of laser energy. In view of the foregoing, there is a need in the art for a detection system that can utilize hollow fiber to reduce the volume, protect the fiber from damage, and achieve low frequency strong resonance in a small volume to compensate for signal strength. Disclosure of Invention In order to solve the technical problems, the invention adopts the following technical scheme: a compact low-frequency resonance photoacoustic Raman detection system based on hollow fiber reinforcement comprises a high-repetition frequency low-energy laser source module, a hollow fiber Raman frequency shifter module, a spiral connection tube type low-frequency resonance photoacoustic cell and a signal acquisition and processing unit, wherein the high-repetition frequency low-energy laser source module, the hollow fiber Raman frequency shifter module, the spiral connection tube type low-frequency resonance photoacoustic cell and the signal acquisition and processing unit are sequentially arranged along an optical path; The device comprises a high-repetition frequency low-energy laser source module, a hollow fiber Raman frequency shifter module, a signal acquisition and processing unit, a differential phase locking processing and concentration inversion unit, a signal acquisition and processing unit and a concentration value acquisition unit, wherein low-energy high-frequency pulse laser generated by the high-repetition frequency low-energy laser source module is focused by a convex lens and is emitted into the hollow fiber Raman frequency shifter module, a bicolor coherent beam output by the hollow fiber Raman frequency shifter module is collimated by an achromatic collimating lens and then coaxially emitted into a spiral connection pipe type low-frequency resonance photoacoustic cell, the excited resonance photoacoustic signal is acquired by a first microp