Showing papers on "Ponderomotive energy published in 1999"

On electron acceleration by intense laser pulses in the presence of a stochastic field

Abstract: Electron acceleration by intense laser pulses is studied in the presence of a stochastic field representing a background plasma. Electron distributions are generated peaked in the direction of laser propagation and having a quasi-thermal energy spectrum. Effective temperatures are obtained above the ponderomotive energy. They scale with laser intensity I0 and interaction time t0 proportional to I01/2t0α with α≈0.5−1.0.

Tunneling Excitation to Resonant States in Helium as Main Source of Superponderomotive Photoelectrons in the Tunneling Regime

Abstract: We present numerical solutions of the time-dependent Schr\"odinger equation in the single-active-electron approximation and calculate wave functions for photoionization of helium exposed to 800 nm light. Electron spectra show $\ensuremath{\sim}200$ peaks up to 272 eV, due to above-threshold ionization. The simulations confirm the existence of a wide, flat plateau in the electron spectrum due to backscattering, between 3 and 8 times the ponderomotive energy. Electrons in this range originate almost exclusively through resonance enhancement by quivering excited states, which in turn are populated by light-induced tunneling from the ground state.

S-matrix theory of above-threshold ionization in a bichromatic laser field

Abstract: We apply the strong-field S-matrix theory to the above-threshold ionization (ATI) in a bichromatic linearly polarized laser field having frequencies and , and the relative phase between the laser field components. The presented theory includes both the Coulomb and rescattering effects. We compute and discuss the electron energy spectra for different angles between the momentum of the ionized electron and the polarization vector of the laser field. We found that the plateau for and for the backward emission of electrons extends up to , where is the ponderomotive energy of the first laser field component (assuming equal intensities of both components). There are no such high-energy electrons for , in contrast to the symmetry , valid in the monochromatic case. In the bichromatic case the ionization rates possess the more general symmetry property . Therefore, for we predict the emission of the high-energy electrons in the forward direction . In a bichromatic field the sidelobe structures are strongly influenced by quantum mechanical interference effects. We also explore the -dependence of the ionization rates for different relative phases , and for those energies which correspond to the classical cutoff law.