Showing papers by "K. Burnett published in 1994"

Saturation of harmonic generation in one- and three-dimensional atoms

Abstract: A commonly used numerical technique for calculating the harmonic spectrum emitted by an atom exposed to an intense laser pulse is the direct integration of the Schr\"odinger equation. We compare the spectra calculated using two different models. The first is in one dimension with an approximate hydrogenic soft-core potential and the second is in three dimensions with a Coulomb potential. We use realistic laser pulse conditions (100 fs,800 nm) and intensities at which there is significant ionization, leading to a saturation of the harmonic-generation process. Although the ionization rates in the two models differ, the harmonic spectra and the positions of the cutoff are remarkably similar. Only a relatively small number of angular momentum states is needed in the three-dimensional calculation to give a reliable estimate of the cutoff, even for intensities at which there is strong ionization.

Spectral, temporal, and spatial characteristics of plasma-induced self-phase modulation of a subpicosecond excimer laser pulse

Abstract: Plasma-induced self-phase modulation and cross-phase modulation in rare gases and air have been investigated using a femtosecond KrF excimer laser focused to peak intensities in the range 1014 - 1015 W cm-2. Spectral blueshifts of up to 2 nm are observed in the KrF laser spectrum which can be qualitatively modeled by assuming tunneling ionization and one-dimensional pulse propagation. When the degree of ionization Z << 1, pump-probe experiments and theoretical results indicate that field ionization occurs over a time equal to about half the pump pulse width. The pump-probe experiments also show that spatial defocusing causes the spectral blueshifting to be spatially dependent, in agreement with a two dimensional pulse propagation model. Plasma-induced cross-phase modulation can also be used to characterize the pulse width and chirp of an ultrashort laser pulse.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Theory of Interactions Between Laser-Cooled Atoms

Abstract: In this paper, we calculate the resulting momentum distribution for the relative motion of two atoms from a cold atomic collision in the presence of a driving field. We consider temperatures well below the Doppler limit of laser cooling. The collisional process acts as a heating mechanism which competes with the frictional forces in the trap. This limits the possible temperatures and densities and has important implications for the formation of a Bose-Einstein condensate in such a trap.