NONEQUILIBRIUM AND BOLOMETRIC RESPONSES OF YBACUO THIN-FILMS TO HIGH-FREQUENCY MODULATED LASER-RADIATION

Picosecond nonequilibrium and slow bolometric responses to infrared ra diation from a patterned high-T-c superconducting (HTS) film in resist ive and normal states deposited onto LaAlO3, NdGaO3, and MgO substrate s were investigated using both pulse and modulation techniques. The re sponse time of 35 ps to a laser pulse of 17 ps FWHM has been observed. The intrinsic response time of the fast process is expected to be abo ut a few picoseconds. The modulation technique, being free from the di sadvantages of pulse methods (poor sensitivity, limited dynamic range) , makes the detailed study of a number of relaxation processes possibl e. Besides the nonequilibrium response, two kinds of bolometric proces ses, namely phonon transport through the film-substrate interface and phonon thermal diffusion in a substrate, manifest themselves in certai n frequency dependences.