ИСТИНА

Nonequilibrium states of HTSC Y-Ba-Cu-O films with a thickness of 300 nm at the temperatures THETA = 80-85 K below the phase transition point THETA(c) congruent-to 91 K have been investigated by a biharmonic pumping (BP) technique. It has been found that as a result of optical excitation by picosecond laser pulses with the energy density of 10^(-4)-10^(-3) J/cm2 at the wavelengths of 1.064, 0.532 and 0.620 mum, thermodynamic equilibrium is attained only after a time delay of more than 1 ns. Both for the above-specified case and for the case with the equilibrium superconductive phase at THETA < THETA(c), we revealed the same specific dip in the self-diffraction efficiency as a function of the BP frequency detuning OMEGA in the spectral range -10 1/cm > OMEGA> -100 1/cm. This dip conservation has been interpreted as a manifestation of a rather slow phase transition being responsible for the pairing of carriers.