Optical nonresonance and two-photon resonance breathers in anisotropic media

Anisotropic optical crystals with two-photon resonance impurity atoms are shown to have three different mechanisms of the formation of breathers depending on the direction of the wave propagation and on the symmetry of the medium. Explicit analytic expressions for the parameters of nonresonance and resonance two-photon breathers of extraordinary waves are obtained. It is shown that, unlike one-photon breathers, for two-photon breathers in the media with quadratic susceptibilities and the crystal classes 3, 3m, 4, 4mm, 6, 6mm, and Kerr media two different structures of the breathers zones are realized.