PHOTOTHERMAL TRANSPORT EFFECTS IN A THICK-FILM YBCO BOLOMETER UNDER MAGNETIC-FIELDS

Thick (similar to 50 mu m) YBCO superconducting film bolometers have b een fabricated to operate in the temperature range 89-92 K. Responsivi ties greater than 1 V/W have been achieved by biasing with a current s lightly less than that of the critical current, and observing the phot ovoltage in the resistive state. The time response of these films due to photo-conduction is slow (ms). The present work concentrates on the resistive transition and the width of the photosignal peak under the effect of applied magnetic fields. The width of the photo-signal peak over the transition is found to be strongly magnetic field dependent a t low field values while at higher field values it has been used to de termine a value for the vortex tilt modulus. Further, it is found that a temperature difference in the position of the photo-signal peak rel ative to that of the dR/dT peak changes with applied field.