Temporal probing of an ultrafast plasma shutter driven by a KrF femtosecond laser system

A femtosecond high-power KrF-laser system was used to create a rapidly ioni zing plasma on a BK7 glass slide and the plasma formation was probed by a s econd laser pulse at 497 nm. During the formation of the plasma the electro n density reaches the critical density for 497 nm. Therefore, the reflectiv ity of the surface rises from a value given by the Fresnel formulas to a va lue close to 100% and the transmission decreases on the same time scale. it is shown that this method permits a precise timing Of two femtosecond lase r pulses at different wavelengths.