Transient flux dynamics in optically irradiated YBCO thin-film switches

A high-current-density, superconducting thin film will exclude a perpendicular magnetic field, produced either by a coil or a magnet. When the film is driven into the normal state by a fast optical pulse, the screening currents decay, allowing flux to enter. The process of flux entry can be observed by measuring the induced voltage across a coil closely coupled to the film. This is equivalent to the operation of an opening switch and can be used to generate fast current pulses. This concept has been experimentally demonstrated in low and high magnetic fields, corresponding to the reversible and irreversible regimes, using 500-nm-thick YBCO films and a 1.064-/spl mu/m, 150-ps pulsed laser. Theoretical analyses of current redistribution in the film associated with the transient flux motion are compared with experimental results. Prospects for applications of this concept are discussed.<>