Theorie der nichtstationären Anregung von Exziton-Polaritonen durch Zweiphotonenabsorption

Theory of nonstationary Exciton-Polariton Generation by Two-photon Absorption A theory of nonstationary two-photon absorption for nonlinear non-centrosymmetric crystals is presented. The time-dependent radiation flux density of the generated polariton beam is calculated under the condition of an ultrashort laser pulse duration T_L ? ΓT^?1 (ΓT is the exciton line width) and a stationary incoherent test field. The “mechanical” response of the excitons and different group velocities of the polariton and the laser and test fields are taken into account. the spatial dispersion of the exciton motion being neglected. With a rectangular laser pulse shape the analytically nonstationary solutions are discussed for identical and for different group velocities of laser and test fields. Using the conservation laws for energy and quasimomentum we illustrate, by considering the polariton dispersion branches, the various possible cases of two-photon absorption in uniaxial piezocrystals.