High sensitivity and stability cavity-enhanced photoacoustic spectroscopy with dual-locking scheme

We present a high sensitivity and long-term stability cavity-enhanced photoacoustic spectroscopy (CE-PAS) system with optical cavity and acoustic frequency dual-locking scheme for trace acetylene (C2H2) detection. The first mechanism involves locking the optical wavelength to the cavity resonance by comparing the phase-sensitive component of the reflected light with a reference signal in a feedback loop. The second locking mechanism controls the gas proportion inside the photoacoustic cell to lock the acoustic frequency, suppressing the drift caused by environmental temperature variation. By minimizing amplitude fluctuations through dual-locking, the sensor achieves improved stability with reduced fluctuations from ±10.12% to ±1.16%. The linear responsivity and excellent linearity of the sensor are demonstrated over a concentration variation spanning four orders of magnitude. Experimental results showcase a minimum detection limit of 1.2 parts-per-billion (ppb) at an integration time of 400s, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 1.37×10-11cm-1·W· Hz-1/2 for C2H2 detection. Long-term stability is within ±2% over a 15-day period. The combination of high sensitivity and long-term stability make this CE-PAS sensor suitable for a wide range of applications in environmental monitoring, industrial process control, and gas leak detection.