Abstract

Atoms exposed to intense laser fields may absorb more photons than necessary for ionization. This effect is called above-threshold ionization. The typical signature of this phenomenon is a series of maxima (ATI-peaks) in the photoelectron energy spectra being separated by the photon energy. According to the expectations of perturbation theory, the intensity of the above threshold peaks decrease steadily with increasing electron energy. However, at intensities above 10¹³ W/cm² and linear laser polarization the high-order ATI-peaks show a plateau which extends up to 10 times the ponderomotive energy U_P, afterwards the peak heights drop quickly. A similar effect is observed in the generation of high harmonics (HHG). There the existence of a plateau offers the possibility of an efficient generation of short wavelength coherent radiation. In contrast to the ATI plateau the HHG plateau ends at 3.2. U_P plus ionization energy E_IP.

© 1996 IEEE