EVIDENCE FOR THE SPECTRAL DEPENDENCE OF NONEQUILIBRIUM PICOSECOND PHOTORESPONSE OF YBACUO THIN-FILMS

The transient voltage photoresponse of current biased YBaCuO thin film s to 20 ps laser pulses of 0.63 and 1.54 mum wavelengths is measured f or temperatures around the superconducting transition region. The fast picosecond decay of the response is followed by a slow nanosecond rel axation which is associated with the bolometric effect. The magnitude of the fast component of the response varies in proportion to the squa re root of wavelength that plausibly reflects multiplication processes of photoexcited electrons via electron-electron scattering and intera ction with high energy phonons.