Ch. Lee et al., Classical calculation of high-order harmonic generation of atomic and molecular gases in intense laser fields - art. no. 043410, PHYS REV A, 6404(4), 2001, pp. 3410
Based upon our previous works [Eur. Phys. J, D 6, 319 (1999); Chin. Phys. L
ett. 18, 236 (2001)], we develop a classical approach to calculate the high
-order harmonic generation of the laser-driven atoms and molecules. The Cou
lomb singularities in the system have been removed by a regularization proc
edure. Action-angle variables have been used to generate the initial microc
anonical distribution that satisfies the inversion symmetry of the system.
The numerical simulation show, with a moderate laser intensity, a harmonic
plateau with only odd harmonics appears. At higher intensities, the spectra
become noisier because of the existence of chaos. With further increase in
laser intensity, ionization takes place, and the high-order harmonics disa
ppear. Thus, chaos introduces noise in the spectra, and ionization suppress
es the harmonic generation, with the onset of the ionization follows the on
set of chaos.