A novel technique to measure the magnetic relaxation of high-temperature superconducting films on ultra-short time scales

A technique to study magnetic flux relaxation in thin films of high-temperature superconductors at times arbitrarily close to the establishment of the critical state is presented. Heating of the film surface by a high-power laser pulse causes a collapse of the critical state profile, with the consequent expulsion of flux through the heated surface. This creates an emf between two contacts on the surface, the time integral of which is related to the number of vortices expelled. Experimental factors affecting the performance of such measurements are discussed.