OPTICAL MIXING IN THIN YBA2CU3O7-X FILMS

High quality, j(c) (77 K) > 10(6) A/cm(2), epitaxial YBa2Cu3O7-x films of 50 nm thickness were patterned into ten parallel 1 mu m wide strip s. The film structure was coupled to a single-mode fiber. Mixer respon se was obtained at 0.78 mu m using laser frequency modulation and an o ptical delay line. Using two semiconductor lasers at 1.55 mu m wavelen gth the beating signal was used to measure the photoresponse up to 18 GHz. Nonequilibrium photoresponse in the resistive state of the superc onductor was observed. Bolometric response dominates up to 3 GHz, afte r which the nonequilibrium response is constant up to the frequency li mit of our registration system. Using an electron heating model the in fluence of different thermal processes on the conversion loss has been analyzed. Ways of increasing the sensitivity are also discussed.