Spectral splitting of high order harmonics of ionizing gases irradiated with ultrashort intense laser pulses

The spectrum of harmonics generated and propagated in ionized noble gas has been analyzed using one-dimensional wave propagation equation. The result shows that the spectral lines of harmonic become broadened and then split into two peaks when the laser intensity is strong enough to ionize the noble gas. The influence of laser parameters and gas pressure on the splitting has been made clear.