THERMAL-MODEL FOR THE BOLOMETRIC RESPONSE OF HIGH-T-C SUPERCONDUCTINGFILMS TO CHOPPED OPTICAL RADIATION

Thermal detectors which convert the incident radiation to heat are fre quently used to give a periodic response to the external signal modula ted at a fixed low-frequency chopping frequency. Many workers have asc ertained the bolometric response of high-quality epitaxial superconduc ting films on different substrates to chopped laser radiation. Based o n these observations we made an a priori assumption that the voltage r esponse of thin film is entirely due to a thermal mechanism, i.e. in t he proposed one-dimensional heat conduction analysis any possible non- equilibrium processes are neglected. A new analytical formula is deriv ed for the mean temperature increase in the superconducting film. This formula generalizes the previously well known analytical approximatio ns. Further we explore a specific numerical example based on experimen tal data for the optical response of a thin (1.5 mu m) high-T-c Bi-bas ed film on an SrTiO3 substrate irradiated by chopped He-Ne laser radia tion (lambda = 633 nm). On the basis of the theory and the chopping fr equency dependence of the peak voltage response an implementation of a new diagnostic method for evaluation of the thermal Kapitza conductan ce at the superconducting film-insulator interface is demonstrated.