Highly sensitive multi-pass enhanced photoacoustic cell based on three spot-ring structure (TSR-MPC)

A highly sensitive photoacoustic cell with three spot-ring (TSR) based on the cylindrical structure is proposed for trace gas detection of acetylene (C2H2). 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 C2H2 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 2.33×10-9cm-1·W·Hz-1/2. The NNEA coefficient of the TSR-MPC was calculated as 1.47×10-9cm-1·W·Hz-1/2.