Frequency shifts of a narrow resonance of OsO4 in an external interferometer due to self-focusing of radiation

Parametric frequency shifts in a CO₂/OsO₄ laser with a nonlinear absorber and an external interferometer were measured. The shifts were interpreted using an aberration-free theory of self-focusing in an external interferometer with a nonlinear absorber. The results indicated that in such a frequency standard system the stability should be higher (~ 10^–14) than in an external cell system, because of the weak sensitivity of the reference resonance to the photodetection regime. The proposed method for control of the shifts due to self-focusing of a Gaussian beam should also ensure a higher (~ 10^–13) frequency reproducibility.