Abstract

High intensity ultrashort laser pulses can be used to study new laser matter interactions in an intensity regime where classical perturbative theories fail. For intensities up to the threshold of ionization, the electric field of an intense laser pulse can induce an extremely anharmonic response in the electrons of gaseous atoms leading to high order harmonic generation. For gaseous targets, the experimentally observed "plateau" and "cutoff" features of the harmonic spectrum have been theoretically explained. However, analytical expressions for the cutoff energy (E_cut) of the plateau are still the subject of discussion. If I_p is the ionization potential of the target material and U_p is the ponderomotive potential of the light field, then the cutoff energy can be expressed as E_cut = I_p + kU_p, where values for the constant k range from 2 to 3.2.¹

© 1994 IEEE