Asymmetry of nonlinear resonances and frequency shifts in stabilized He–Ne/127I2 lasers

An experimental investigation was made of modulation frequency shifts of radiation from stabilized He–Ne/¹²⁷I₂ lasers (λ=633 nm) which occurred when the frequency deviation changed. It was found that the lens-like properties of the absorbing medium were not the dominant cause of the observed shifts. It was concluded on the basis of a theoretical analysis that the most probable cause of an asymmetry of the nonlinear resonances and of the modulation shifts resulting from them in He–Ne/I₂ lasers was an asymmetry of the absorption coefficient caused by collisions involving a velocity change.