Tuning mode-coupled laser oscillator, compares laser fluctuation frequency with reference, to determine resonance length adjustment from beat frequency

摘要

The laser (1) is initially decoupled. A sample of the self-adjusting laser frequency (fRT) is compared with an external frequency reference (fref) corresponding with the later operational frequency of the mode coupler (5, 6). Phase detectors (8.1-8.3) determine the phase relationship between laser beam intensity fluctuations and the reference signal. The beat frequency generated is used to derive the departure of resonator length from optimum, using a known relationship. The beat frequency is converted by Fourier transformation into a value which is a function of actual resonator length, the result being applied to alter it. Iterative repetition ensues, until the resultant curve exhibits a marked minimum.