Generation of narrow-band ultrasound with a long cavity mode-locked Nd:YAG laser

Abstract
A passively mode-locked, flashlamp-pumped Nd:YAG laser with a cavity length of 11.19 m has been developed to study the noncontact generation of narrow-band ultrasound. The individual mode-locked pulses acted as separate sources of ultrasound, producing a train of acoustic pulses with a repetition rate of about 13.4 MHz. The ultrasound was generated in an aluminum sample and remotely detected with a path stabilized Michelson interferometer. The energy in the multiple pulse acoustic signal was confined to a considerably reduced spectral range compared with that in a single pulse.