INFLUENCE OF GRAIN-BOUNDARY WEAK LINKS ON THE NONEQUILIBRIUM RESPONSEOF YBACUO THIN-FILMS TO SHORT LASER-PULSES

The transient voltage response in both epitaxial and granular YBaCuO t hin films to 80 ps pulses of YAG:Nd laser radiation of wavelength 0.63 and 1.54 mum was studied. In the normal and resistive states both typ es of films demonstrate two components: a nonequilibrium picosecond co mponent and a bolometric nanosecond one. The normalized amplitudes are almost the same for all films. In the superconducting state we observ ed a kinetic inductive response and two-component shape after integrat ion. The normalized amplitude of the response in granular films is up to five orders of magnitude larger than in epitaxial films. We interpr et the nonequilibrium response in terms of a suppression of the order parameter by the excess of quasiparticles followed by the change of re sistance in the normal and resistive states or kinetic inductance in t he superconducting state. The sharp rise of inductive response in gran ular films is explained both by a diminishing of the cross section for current percolation through the disordered network of Josephson weak links and by a decrease of condensate density in neighboring regions.