High finesse membrane-free plano-concave optical detector for photoacoustic sensing

Acoustic sensors with high sensitivity and broadband response are essential for high-precision signal detection technology. In this paper, a high finesse membrane-free Fabry-Pérot (F-P) cavity structure is proposed based on a plano-concave resonator. By further enhancing the end-face reflectivity of the cavity, strong light confinement (Q-factor > 10⁶) is achieved. The membrane-free all-optical detector based on this structure exhibits a sensitivity increased by two orders of magnitude, with a minimum detectable pressure (MDP) of 0.3 mPa/Hz^1/2 @ 1k Hz. The flat response range was 1 Hz-10 kHz with a sensitivity fluctuation of ±2 dB. Moreover, the designed sensor has a compact size of 14 mm×Φ10 mm. These excellent characteristics hold great potential for high-performance photoacoustic sensing technologies.