4<i>l</i>-PBD: a probe beam deflection system with quadruple coupling length for acoustic detection

In this Letter, we present a quadruple acousto-optic coupling length-enhanced acoustic detection system, i.e.,4<i>l</i>-PBD, based on light probe beam deflection methodology. By leveraging polarization multiplexing and the non-reciprocal characteristics of Faraday rotator mirrors, the effective acousto-optic coupling length is quadrupled, thereby amplifying the angular deflection of probe beams. Both numerical simulations and experimental validations conclusively demonstrate the effectiveness of the 4<i>l</i>-PBD architecture. This design provides a promising solution for precise measurement of weak acoustic pressure signals, particularly in applications requiring high-sensitivity non-contact detection.