VIBRATION DETECTION USING DYNAMIC PHOTOREFRACTIVE GRATINGS IN KTN/KLTN CRYSTALS

We demonstrate a sensitive, all-optical, self-aligning holographic microphone/vibration sensor utilizing the zero external electric field photorefractive (Zefpr) effect. The device relies on the unique phase relationship, phi = 0, between a spatially periodic intensity standing wave and the resultant index grating created with the Zefpr effect. Under this zero phase condition, the transmitted intensity of interfering beams in a two beam coupling geometry varies linearly with displacement of either the index grating or one of the interfering beams. In this way, vibrations are sensed remotely without any electrical signals in the vicinity of the sensor. The sensitivity of the microphone was determined as a noise equivalent power of 15 dB sound pressure level relative to 0.0002 mubar across the range 1.6-15.5 kHz.