A method for setting the optimum cavity length for a mode-locked laser oscillator

A method for setting the optimum cavity length for a mode-locked laser oscillator, is coupled a fraction of the laser radiation circulating in the resonator and supplied with a reference frequency and the optimum cavity length is determined by evaluating the frequency difference determined, characterized, in that which adjusting intracavity laser radiation with the rotational frequency (f by the phase relation between the radiation in the laser amplitude fluctuations and spontaneously occurring by unsynchronized superposition of several modes of the reference signal by means of phase detectors (8.1, 8.2, 8.3) is determined and from the beat spectrum by means of Fourier transformation, a value is determined as a function of cavity length and actual applied, thereafter, the cavity length changes, and the rotational frequency (f