Analysis of the influence of fluctuations of the reference frequency and of the resonator length on the frequency instability of a gas laser and requirements to be satisfied by automatic frequency control systems

An analysis is made of technical fluctuations of the emission frequency of a gas laser with an automatic frequency control (AFC) system. The minimum instability of the emission frequency in a time τ is found as a function of τ and of the spectral densities of fluctuations of the reference frequency and of the optical length of the resonator, photodetector and amplifier noise, and parameters of the forced frequency modulation of the output radiation. The transfer function is found for an optimal linear AFC system ensuring minimum instability. The experimental results are given of a determination of the spectral densities of perturbations and of the relative frequency instability. Practical recommendations are given on the design of optical resonators and AFC systems.