Wave-front reversal in a medium with inhomogeneities and an anisotropic wave spectrum

The possibility of parametric wave front reversal that involves waves of different nature with substantially different values of group velocity, wave number, and dissipation parameter is demonstrated. This phenomenon takes place in the system of microwave spin waves having anisotropic spectrum and propagating in yttrium-iron garnet films with defects. In our experiment fast input magnetostatic waves (MSW's) having wave vector k~10²0.3em0exrad∕cm and frequency 4.70.3em0exGHz were elastically scattered on defects and inhomogeneities of the YIG film and transformed into slow long-lifetime dipole-exchange spin waves (DESW's) of the same frequency having wave vector of the order of k~10⁴0.3em0exrad∕cm. Then, a short pulse of double-frequency parametric pumping was applied to perform wave front reversal for these DESW's. The reversed DESW's were scattered on the same defects, forming, as a result, an output delayed MSW signal. The dissipation parameter of DESW's was determined experimentally and turned out to be three times smaller than the dissipation parameter of the MSW signal, thus creating a possibility of low-loss delay of microwave pulsed signals.