High-sensitivity acetylene detection system using ellipsoid multi-pass cell (EMPC) based on the opposite dual optical source

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 Φ28mm×100mm and the size of the buffer cell at both ends of the PA cell is Φ70mm×10mm. 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 2f 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 was9.84×10-8cm-1·W·Hz-1/2. The whole system has high detection sensitivity and stability.