Shifts of the emission frequency of a third-harmonic-stabilized laser due to saturation of the refractive index

A laser with an internal absorption cell stabilized with the aid of its third harmonic is investigated. Considerable frequency shifts are observed when the gas pressure in the cell, depth of modulation, and intensity of the saturating field are altered. These shifts are attributed to the appearance of lens-like properties in the absorbing medium under the action of a resonant field with a Gaussian intensity distribution.