Resonance-parametric mechanism of optical rectification and high harmonic generation

The generation of zero and high-order harmonics in the spectrum of a laser pulse propagating through a medium containing quantum particles whose constant resonance transition dipole moment is nonzero is studied theoretically. The consideration is performed in the approximation of slowly varying envelopes modified for the case of the medium with the nonzero permanent dipole moment. It is shown that this modification requires consideration of antiresonance terms, in particular, the Bloch-Siegert shift in equations. The conditions are revealed for the efficient optical rectification and excitation of the second harmonic at a quasi-monochromatic signal applied to the medium.