Spectral, temporal, and spatial characteristics of plasma-induced spectral blue shifting and its application to femtosecond pulse measurement

The spectral, temporal, and spatial characteristics of plasma-induced spectral blue shifting in atmospheric-density rare gases were investigated by a two-color pump–probe technique. When the degree of ionization is less than 1, experiments and theoretical results show that field ionization occurs over a time approximately equal to half the pump-pulse width and that ionization-induced defocusing causes spectral blue shifting to be spatially dependent. The pulse width of a 147-nm pulse generated by four-wave mixing of a femtosecond KrF laser pulse in xenon was determined to be 400 fs by a cross-correlation technique based on plasma defocusing.