On the mechanism of anomalous ellipticity dependence of high-order harmonic generation in intense laser fields
(Physics Department, Kansas State University, Manhattan, KS 66506),
(Department of Chemistry, University of Kansas, Lawrence, KS 66045)
Based on the weak field approximation, the high-order harmonic generation (HHG) yield should decrease monotonically as the ellipticity of a laser field increases. In the experiment, for certain HHG, the observed HHG yield may increase as the ellipticity of the laser field increases. Here we investigate the mechanism of this anomalous ellipticity dependence of the HHG spectra by solving the time-dependent Schrödinger equation. Two kinds of anomalous ellipticity dependence of the HHG spectra have been found. One appears near the ionization threshold and another appears in the cut-off regime. The near ionization threshold one is originated from the near-resonance due to the ac Stark shift and such an enhancement strongly depends on the laser intensity, wavelength as well as atomic structure. The one in the cut-off regime is due to that the higher energy photo-electron is confined by the circular component of the field and emits a HHG.
This work was supported by the
Chemical Sciences, Geosciences and Biosciences Division,
Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.
Submitted to DAMOP, May 2004 in Tucson, AZ.
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