Fast infrared response of YBCO thin films

This paper reports on epitaxial thin films of superconducting YBCO by sputter deposition and by electron-beam evaporation. The sputter-deposited films were grown in-situ by rf magnetron sputtering from a single 8-inch diameter target onto substrates of MgO, LaAlO3, and LaGaO3 heated to 650--725 degrees C. By placing the substrate in the center of the magnetron racetrack and using a grounded shield to avoid negative ion bombardment, highly c-axis oriented films with Tc = 87 K were obtained. The evaporated films were prepared by coevaporation of Y, BaF2, and Cu onto SrTiO3 followed by post annealing in wet oxygen. The films have been used to investigate the interaction of YBCO with pulsed infrared laser radiation. Pulses 100 psec long from a Nd:YAG laser (λ = 1.06 μm) were directed onto a current biased line patterned into the superconducting film. It was found that the response was essentially bolometric in nature but with indirect evidence of nonequilibrium hot-electron transport. Fast switching (1 ns rise) of optically thick films could be obtained either by biasing the switch close to the critical current or by cooling the film below about 20 K. These results, which are similar to our earlier results with granular YBCO films, are encouraging for potential application to a high-current optically-triggered opening switch