Electromagnetic plasma computer simulations are used to analyze the frequency shifts caused by the ionization of atmospheric-density noble gases during interaction with intense femtosecond laser pulses; the results are presented and compared with experimental data. The simulations trace the temporal evolution of plasma growth during the femtosecond ionizing pulse and calculate the resulting self-induced blue shift of the ionizing pulse spectrum. Variations with pulse intensity, gas pressure, and gas species are calculated. The relative contributions of strong-field ionization and electron-impact ionization on the frequency shifts are discussed. The simulations provide qualitative explanations of most of the features observed experimentally in the blue-shifted spectra. The technique of spectral blue shifting intense femtosecond laser pulses provides a new diagnostic tool for studying strong-field ionization and laser-induced breakdown in dense plasmas.
© 1992 Optical Society of America
Original Manuscript: January 24, 1992
Published: November 1, 1992
B. M. Penetrante, W. M. Wood, C. W. Siders, J. N. Bardsley, and M. C. Downer, "Ionization-induced frequency shifts in intense femtosecond laser pulses," J. Opt. Soc. Am. B 9, 2032-2040 (1992)