The spectrum of harmonics generated and propagated in ionized noble gas has
been analyzed based on one-dimensional wave propagation equation. It shows
that the spectral lines of harmonic become broaden and then split into two
peaks when the laser intensity is strong enough to ionize the noble gas. T
he relation of splitting upon laser parameters and gas pressure has been fo
und. (C) 2000 Elsevier Science B.V. All rights reserved.