PURPOSE: To stably maintain single frequency oscillation, by performing automatic control in the on-line real time manner wherein, after the travelling direction of a resonator mirror is inverted on the basis of measured values of oscillation delay time and its irregularity, the inversion is not again performed during movement of a specified number of steps.
CONSTITUTION: By performing initial scanning, a rear mirror 6 is moved at the position where the minimum oscillation delay time has been obtained. The laser light waveform is measured with a transient recorder 13, and outputted to a computer 9. It operates the average value and the irregularity of oscillation delay time measured and stored for each of the waveform data, and compares them with the set values of the past minimum oscillation delay time and irregularity. When a specified condition is satisfied, a signal for driving a piezo element 7 in the direction opposite to the former direction is outputted to a piezo driver 8. However, after the step sending direction is inverted, the inversion is not again performed independently of the measurement results, until a specified number of steps.
SATO TAKESHI
MATSUTOMI SHOKICHI
