Abstract

Plasma-induced spectral blueshifting in rare gases has been investigated using a subpicosecond KrF excimer laser focused to a peak intensity in the region of 10¹⁴ W/cm² (adiabaticity parameter in the range 8 < γ < 10). Blueshifts of up to 2 nm have been observed, and the blueshifted spectrum shows an interference-like oscillatory structure. By comparing experimental results with numerical simulations, the blueshifted spectra are shown to be the result of plasma-induced self-phase modulation, and can be modeled qualitatively by assuming tunneling ionization and one-dimensional pulse propagation. Under the condition of weak ionization, pump-probe experiments and theoretical results show that field ionization occurs over a time equal to about half the pulse width. A two-dimensional pulse propagation model indicates that spatial defocusing causes spectral blueshifting to be spatially dependent.

© 1993 Optical Society of America