Biexponential decay and delay artifact in the photoresponse of superconductors

The photoresponse of superconductor exposed to narrow and wide laser pulses is examined in terms of the superconductor´s impedance. The impedance helps to identify the causes and the origins of the fast and slow photoresponse decay in YBCO and Nb. The source of the asymmetrical photoresponse signals in Pb is explained in terms of impedance nonlinearities with temperature. Finally, the impedance model is used to explain what has been previously identified incorrectly as delayed photoresponse signals in In and Pb. All these temporal manifestations are produced by the impedance and are not indicative of a delayed response or of intrinsic or sudden changes in the recombination-generation lifetimes in the superconductor.<>