Optical detection of ultrasound with a microchip laser

A novel optical ultrasonic detector that relies on frequency modulation of a microchip laser is proposed and demonstrated. When the laser is placed in a time-varying acoustic field, the microchip laser cavity length is periodically modulated, creating a frequency-modulated optical output in which the frequency shift is linearly proportional to the acoustic-wave amplitude. With a confocal Fabry-Perot slope filter and a Nd:YAG microchip laser operating at 1.06 microm, a detector response of 7.5 MHz/kPa was measured at an acoustic frequency of 7.75 MHz. A one-dimensional acoustic model is developed to explain the observed detector performance.