Measurement of the frequency fluctuations of a laser with a nonlinear-absorbing cell using the Bershtein method

Abstract

We propose to use the method of I. L. Bershtein for measuring the frequency fluctuations of an arbitrary type oscillator from the error signal at the output of the phase locking system for a laser with internal absorbing cell. The spectral density of the frequency fluctuations of a single-frequency He-Ne/CH4 laser was measured. It is shown that in this case the method allows us to measure the low-frequency technical fluctuations of the laser frequency, which determine the width of the laser emission line. The measurements can be performed in the case of both suppression of low-frequency fluctuations of the laser frequency due to the phase locking system and the regime that is close to that of free generation. It is also shown that an increase in the operating frequency band of the phase locking system makes sense only in the case in which the reference spectral density of the laser frequency fluctuations multiplied by the slope of the frequency discriminator conversion (in this case, the power and photoreceiver peak) exceeds the noise level at the system input.