Losses of high-intensity optical radiation in transparent nonlinear media

One of the possible mechanisms of loss of energy by high intensity optical radiation in media with a quadratic nonlinearity is considered. The source of losses is nonphase-matched secondharmonic generation when the doubled frequency lies within an absorption region of a crystal. A detailed study is reported of the influence of absorption at the second-harmonic frequency on the propagation of the fundamental-frequency wave for different ratios of the characteristic lengths (absorption, nonlinear, coherence, and quasistatic). It is shown that in some cases nonlinear losses of the fundamental-frequency radiation may be considerable and can limit the efficiency of phase-matched nonlinear optical processes.