Applications and accuracy improvement of vibrometer using frequency modulated self-mixing laser diode

Recently, we have reported a new compact vibrometer employing a self-mixing laser diode (SM-LD) which is modulated by a triangular current. The measurement principle of displacement is based on time integration of each sampled velocity, which is measured during every one period of the triangular modulation. In this paper, we proposed to automatically improve the measurement accuracy of the new vibrometer by adjusting a sampling frequency, i.e., the frequency of the triangular current in accordance with an equation which gives a proper sampling frequency to realize a required error. When measuring a sinusoidal amplitude more than 10 /spl mu/m through 39 /spl mu/m, an accuracy more than 98% is realized. Some aperiodic displacement waveforms of various vibrating bodies have successfully been measured.