Frequency fluctuations in a gas laser with nonlinear absorption

Technical fluctuations of the frequency of a gas laser with nonlinear absorption are analyzed theoretically. The spectrum of frequency fluctuations is calculated for a laser with automatic frequency stabilization and an external automatic frequency control (AFC). The frequency instability σ(τ) is calculated as a function of the averaging time τ, the time constant of the automatic frequency control circuit τ₀, and of the nonlinear frequency pulling factor S. The limiting values of the short-term and long-term stability are deduced allowing for the intrinsic noise of the AFC circuit. A frequency-stabilization system with two nonlinearly absorbing cells (tandem system) is discussed. It is shown that this system can raise considerably the short-term and long-term stabilities by automatic frequency stabilization.