A novel optical ultrasonic detector that relies on frequency modulatio
n of a microchip laser is proposed and demonstrated. When the laser is
placed in a time-varying acoustic field, the microchip laser cavity l
ength is periodically modulated, creating a frequency-modulated optica
l 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 mum, 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 detect
or performance.