Laser vibrometer using GaAs adaptive photodetectors based on the effect of the non-steady-state photoelectromotive force

We report on simple high-sensitivity interferometric technique of detecting Fibrations and present characteristics of laser vibrometer using GaAs adaptive photodetectors based on the effect of the non-steady-state photoelectromotive force. It enables efficient direct conversion of high-frequency phase modulation of speckle-like optical wave reflected from the vibrating object into an output electrical signal with concomitant setting of optimal operation point of the interferometer and suppression of amplitude laser noise. The results of measurements of small vibration amplitudes of the mirror and diffusely scattering objects are presented Preliminary studies at 1.06 mu m showed that it is possible to detect ultrasonic vibrations with the amplitude of 0.2 Angstrom with a signal po ser of 20 mW and a bandwidth of 15.5 MHz. The sensitivity of GaAs adaptive photodetectors at 0.63 mu m was found to be 0.1 Angstrom for excitation frequency 1 kHz, registration bandwidth 1 Hz and average laser power on the photodetector 200 mu W. This optical phase-to-electrical signal converter is not sensible to ambient vibrations, thermal drift, amplitude laser noise and is therefore appropriated for industrial applications.