Search

A photoacoustic spectroscopy (PAS) based on vertical cruciform multi-stepped photoacoustic cell (CMS-PAC) was developed to achieve highly sensitive detection of trace acetylene (C 2 H 2) gas. Compared with the T-type PAC, the CMS-PAC has improved sensitivity through optimization of both the structural design and the direction of laser incidence. Through finite element simulation analysis, when the incidence direction of modulated laser was placed horizontally, the acoustic intensity of the CMS-PAC was ∼2.45 times higher than that of the T-type PAC. When the modulated laser was applied vertically, the acoustic intensity achieved by the CMS-PAC was ∼11 times higher than that along the horizontal incidence direction. The sensitivities of the CMS-PAC-based PAS system have reached 15.06 and 1.83 pm/ppm, along the vertical and horizontal directions, respectively. Combined with assessment using Allan deviation, the CMS-PAC-based PAS system achieved a minimum detection limit of 3.04 ppb@100 s in the vertical direction, and 23.06 ppb@100 s in the horizontal direction. The proposed CMS-PAC not only enhances acoustic intensity through optimized resonant cavity structures but also improves detection sensitivity with the optimized direction of laser incidence, providing a novel perspective for designing highly sensitive and compact PACs. • We propose a vertical cruciform multi-stepped photoacoustic cell. • There are two directions of laser incidence perpendicular to each other. • The proposed new photoacoustic cell has advantages of compact size. • The proposed new photoacoustic cell has better detection sensitivity. [ABSTRACT FROM AUTHOR]

Abstract: An all-optical photoacoustic spectrometer based on the diaphragm-based extrinsic Fabry–Perot interferometer (EFPI) fiber acoustic sensor for trace gas detection at atmospheric pressure and room temperature is first developed. The diaphragm-based EFPI fiber acoustic sensor is used to replace the conventional acoustic sensor in this system. Tunable erbium-doped fiber ring laser (TEDFRL) with an erbium-doped fiber amplifier (EDFA) is used as the excitation light source for the generation of the photoacoustic (PA) signal. A first longitudinal resonant PA cell with double absorption optical path is used to improve the sensitivity of the system. The advantages of all-optical photoacoustic spectrometer are immunity to electromagnetic interference, safely in flammable and explosive situations, and long distance sensing. This system is developed for the continuous and real-time measurement of acetylene gas at room temperature and atmospheric pressure. With the wavelength modulation and lock-in harmonic detection method, the minimum detectable limit of 1.56 parts-per-billion (ppb) volume acetylene (signal-to-noise ratio, SNR=1) at the 1530.37nm transition line was achieved. [Copyright &y& Elsevier]

A highly sensitive photoacoustic cell with three spot-ring (TSR) based on the cylindrical structure is proposed for trace gas detection of acetylene (C 2 H 2). In the resonant cavity, the acoustic characteristic of the three spot-ring multi-pass cell (TSR-MPC), such as the resonance frequency, the distribution of the acoustic pressure and the acoustic pressure level, are simulated. The internal optical path of the TSR-MPC is given in the paper. The optical path length of the TSR-MPC is about three times of the traditional multi-pass cell, which is about 10.2 m with 51 reflections. Combined with a distributed feedback (DFB) laser with the center wavelength was located at C 2 H 2 absorption line of 1531.588 nm, the sensor system was established to verify the feasibility. Experimental results show the normalized noise equivalent absorption (NNEA) coefficient of the traditional MPC was calculated as 2.33 × 10 - 9 c m - 1 · W · H z - 1 / 2 . The NNEA coefficient of the TSR-MPC was calculated as 1.47 × 10 - 9 c m - 1 · W · H z - 1 / 2 . [ABSTRACT FROM AUTHOR]

A multi-pass cell with ellipsoid structure used dual optical source of opposite side was proposed firstly in this paper. The EMPC was composed of double concave spherical mirrors and an ellipsoidal resonator. The radius of curvature of the two symmetric concave spherical mirrors was 200 mm and the length of the cavity was 120 mm. The size of the resonator of the photoacoustic (PA) cell in the experiment is Φ 28 m m × 100 m m and the size of the buffer cell at both ends of the PA cell is Φ 70 m m × 10 m m. The two laser beams were injected from the two sides of the concave spherical mirrors by the optical fiber. The absorption spectrum line with the acetylene wavelength of 1531.58 nm was selected. The simulation results show that the light beam can be reflected 37 times in EMPC and the optical path length can reach 8.64 m. In the experiment, the 2 f signal peak value fitting curve obtained at different concentrations with good linearity. Allan deviation analysis of experimental results shows the detection limit of EMPC was 60 ppb when the average time was 2 s. When the average time was 2 s, the normalized noise equivalent absorption (NNEA) coefficient of the system was 9.84 × 10 - 8 c m - 1 · W · H z - 1 / 2 . The whole system has high detection sensitivity and stability. [ABSTRACT FROM AUTHOR]

In this paper, a new type of ellipsoid photoacoustic cell was designed to enhance the photoacoustic effect for the first time. The COMSOL Multiphysics software was used to stimulate the acoustic characteristics of the traditional cylindrical photoacoustic (PA) cell and the ellipsoid PA cell. The resonance frequency, acoustic pressure distribution and acoustic pressure level size in the resonant cavity of the novel PA cell and traditional cylindrical PA cell were analyzed. The novel PA cell was used to detect the concentration of acetylene. In the experiment, the 1532.83 nm absorption spectral line was selected as the measurement spectral line, and the tunable Distributed Feedback (DFB) semiconductor laser was finally selected as the light source. Fabry–Perot (F-P) fiber optic acoustic sensor which has been reported in other paper was used to collect the sound pressure signal. The signal-to-noise (SNR) of the cylindrical photoacoustic spectral system for the detection of acetylene gas was 23 dB, and the detection limit sensitivity was 2.17 ppb. The SNR of the ellipsoid photoacoustic spectral system for the detection of acetylene gas was 34 dB, and the detection limit sensitivity was 1.47 ppb. The performance of the ellipsoidal photoacoustic cell is better than that of the cylindrical photoacoustic cell. The results shown that the novel PA cell can improve the PA effect significantly. [ABSTRACT FROM AUTHOR]

Photoacoustic spectroscopy (PAS) can be utilized as an ultrasensitive gas detection method. The basic principles of gas detection using PAS are discussed in this paper. First, the basic instrumentation for a PAS gas detection system is introduced focusing on the photoacoustic cell. The discussion includes non-resonant photoacoustic cells and the different types of resonant photoacoustic cells, including the longitudinal photoacoustic cell, the Helmholtz photoacoustic cell, the T-type photoacoustic cell, and the high-frequency resonant photoacoustic cell. The basic working principles of each of these, cells as well as the advantages and disadvantages of photoacoustic cells are discussed, and the development of newer types of photoacoustic cells in recent years is outlined in detail. This review provides detailed reference information and guidance for interested researchers who would like to design and build advanced photoacoustic cells for gas detection. Graphical abstract This is a visual representation of the abstract. [ABSTRACT FROM AUTHOR]