Stabilized gas-discharge laser with an external absorption cell in the gain-modulation regime

A theoretical analysis is presented of the frequency shift of a gas laser stabilized by absorption in an external cell; the shift is caused by gain modulation and parasitic (environmentally determined) frequency modulation effects on the frequency locking system. In the case of combined gain and frequency modulation, the shift occurs not only when the frequencies of perturbations coincide with harmonics of the reference signal of the locking system, but also at combinational frequencies. For this reason, an analysis of frequency fluctuations which takes separate account of gain and frequency perturbations is inadequate. The instability of the scale factor of a ring laser stabilized by an external cell is investigated.