Light-induced gratings in a medium exhibiting two-photon absorption
An analysis is made of the excitation of transient gratings as a result of the interaction of ultrashort pulses with a medium characterized by a two-photon nonlinearity. The amplitudes of the spatial modulation of the gratings are described by fourth-order correlation functions of a pulse and in the absence of phase modulation one of these functions is identical with a two-photon absorption trace (profile) measured by a traditional method. The spectral or angular distribution of the radiation diffracted by such gratings is linked uniquely to the amplitudes of their spatial modulation. A practical method is suggested for the study of ultrashort pulses: this method is free of the influence of the background and contrast, is independent of the luminescence mechanism, and can be used in conjunction with traditional methods.