Degenerate four-photon probing of the kinetics of a nonlinear response of high-temperature superconductors in pump–probe spectroscopy

It is shown that the spectral–temporal and temperature "anomalies" of the kinetics of reflection and transmission coefficients of high-temperatures superconductors (HTSCs) at high "impact" excitation levels have direct analogies also in the case when the instant state of samples is probed by using the self-diffraction of probe pulses made coincident in time and propagating at an angle to each other. The possibility of using the transient modification of the method of degenerate four-photon spectroscopy for the HTSC diagnostics substantially expands the scope of experiments that can confirm or refute the correctness of the model based on the consideration of the contribution of interband electronic transitions to the response of an excited HTSC film with the "frozen" energy gap.