Initiation of laser chemical reactions by automatic phase locking in stimulated Raman scattering in a molecular gas

An analysis is made of the possibility of using stimulated Raman scattering in a biharmonic visible or ultraviolet field for the excitation of one of two coupled anharmonic molecular modes whose sum frequency is close to the difference frequency of the biharmonic field. The coupling between the modes and the fields is due to electrooptic anharmonicity in relation to the polarizability and a resonance is maintained by automatic phase locking. It is shown that such excitation of anharmonic modes may occur at power densities of the field harmonics ~10 MW/cm² or less. A system of equations of motion is derived for the process under discussion.