Influence of the wavefront curvature on the position of a stabilized laser frequency under frequency modulation conditions

A calculation was made of the shift of a stabilized frequency of a laser with a nonlinear absorption cell operating under frequency modulation conditions. An allowance was made for the curvature of the wavefront of the resonator field. It was found that the amplitudes of the shift and of a parasitic signal observed in the line wing depend on the direction of observation (to the right or left) of the resonator.