T-Type Photoacoustic Sensor Based on Multiple Reflection of Light Beams

Photoacoustic spectroscopy plays an important role in the field of gas detection due to its advantages of high sensitivity and good selectivity. To improve the photoacoustic detection performance without increasing the volume of devices and the reflective mirrors, a T-type photoacoustic cell on the basis of the resonant photoacoustic technology is developed, which is composed of an absorption cell with gold-plated inner walls and an acoustic resonance tube. The gold-plated boards are used to replace the traditional optical windows at both sides of the absorption cell. At the same time, the optical fiber collimator is fixed on the board to make the light beam reflect multiple times in the absorption cell, which can increase the equivalent absorption path of the gas samples. The improvement in detection performance by the proposed method is verified by mathematical modeling, theoretical derivation, finite element simulation, and experimental analysis. The signal-to-noise ratio (SNR) of the proposed method is 14.6 times higher than that of the traditional light beam excitation mode when the phase-locked integration time is 1 s, and the single detection time is 5 s. On this basis, a CO2 photoacoustic detection device is built. The experimental results reveal that the lowest limit of detection for CO2 samples is 15x10(-6), and the normalized noise equivalent absorption coefficient is 11. 9x10(-9) cm(-1)center dot W center dot Hz-1/ 2.