Doppler-free resonances of the second-order Raman scattering

An analysis is made of the possibility of observation of Raman scattering resonances free of the influence of the Doppler effect. Such Doppler-free resonances result from the excitation of a standing wave of Raman vibrations in a gas by two standing optical waves differing in frequency by half the Raman frequency. Complete compensation of the Doppler shifts occurs as a result of simultaneous interaction of atomic particles with two pairs of counterpropagating waves. Scattering of traveling pump waves by a standing wave of Raman vibrations in the fifth order with respect to the field gives rise to resonances in the radiation at the Stokes and anti-Stokes frequencies. Coherent scattering is observed in the presence of dispersion. A resonance in the number of particles excited to the upper level of a Raman transition appears in the eighth order in the field. The expressions obtained are applied to the specific example of neon.