A highly accurate semiclassical method for high-order harmonic generation

We extend our recently developed semiclassical strong-field Herman-Kluk (SFHK) method to calculate high-order harmonic generation (HHG) from atoms and molecules in intense lasers. We show that our method, based on a combination of the Herman-Kluk propagator and the strong-field approximation, can provide highly accurate for both HHG spectrum and phase, comparable to those from the exact numerical solutions of the time-dependent Schrodinger equation. We provide detailed analyses of our method and its applications to the HHG process, particularly the analyses of the recombination time. The main computational task in this method is to solve the classical Newton equations for the active electron in the combined atomic (or molecular) potential and laser-electron interaction. The motion of the centers of the electron wave packets, modeled by coherent states, is governed by independent classical trajectories so that the computation can therefore be parallelized very efficiently. The method can be extended to polyatomic molecules in a straightforward manner.

This work was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under Award Number DE-SC0023192.