Photoresponse of high Tc superconductor thin films

A fast photoresponse is observed in a current-biased epitaxial YBa 2 Cu 3 O 7 thin-film bridge structure exposed to 100 ps laser pulses. A bolometric response, with a pulse width of the order of 10 ns, dominates at temperatures close to T c and at high laser fluences. At lower temperatures and fluences, the observed transient response contains distinct fast and slow components. Preliminary results indicate a pulse width for the fast component less than 500 ps. Application of a small magnetic field perpendicular to the sample increases the amplitude of the slow component while leaving the fast component relatively unaffected. Comparison of these results with resistance versus temperature measurements in the same magnetic field suggests that the fast component is nonthermal in origin.