Picosecond photoresponse of YBa2Cu3O7−x thin films

The photoresponse of current-biased YBa2Cu3O7−x (YBCO) microbridges, patterned in 100-nm-thick, high-quality epitaxial films on LaAlO3, has been characterized by means of an electro-optic sampling technique. The photoresponse from 100-fs laser pulses (390-nm wavelength) was measured to be in the form of Gaussian-shaped pulses with the width as short as 0.8 ps. The physical origin of the photoresponse signal can be attributed to a nonequilibrium electron heating mechanism. The measured signal represents, in our opinion, the intrinsic photoresponse of YBCO.