Remote eavesdropping at 200 meters distance based on laser feedback interferometry with single-photon sensitivity

•Eavesdropping clear speech within 100 meters and recognizable one within 200 meters•Less than 0.91 photon sensitivity per feedback cycle•Support a range of incidence angle in ± 60° in the distance of 100 meters•Support a range of incidence angle in ±30° in the distance of 200 meters•Meet various requirements of acoustic signals detection