Abstract

High-order harmonic generation in the strong-filed limit has successfully been modeled by a quasistatic picture based on the tunneling ionization of an atom, acceleration of the electron in the continuum, and recombination to the atomic ground state.^1,2 The experiments reported so far support this model, especially by demonstrating the theoretical prediction that the q th high harmonic with photon energy hv_p much in excess of the atomic ionization potential I_p is very sensitive to the laser ellipricity ε = E_y/E_x^3–5 This model, however, cannot be applied to the generation process of harmonics with hv_q, less than I_p The origin of such harmonics still appears to be unclear, although some possible mechanisms have been proposed.^4,5

© 1996 Optical Society of America