Calculations of population transfer during intense laser pulses
Abstract
Recent experiments by several groups have examined the question of population transfer to resonantly excited states during intense short laser pulses, in particular the amount of population that remains 'trapped' in excited states at the end of a laser pulse. Calculations of population transfer and resonant ionization in xenon at both 660 and 620 nm are presented. At the longer wavelength, the seven photon channel closes at 2.5 x 10(exp 13) W/cm(exp 2). Pulses with peak intensities higher than this result in 'Rydberg trapping', the resonant transfer of population to a broad range of highlying states. The amount of population transferred depends on both the peak intensity and pulse duration. At 620 mm there are numerous possible six photon resonances to states with p or f angular momentum. A large number of calculations were performed for 40 fs pulses at different peak intensities and the population transferred to these lowlying resonant states were examined as a function of the peak laser intensity. We do not have room to comment upon the resonantly enhanced ionized electron energy spectra that we also determine in the same calculations. Our calculations involve the direct numerical integration of the timedependent Schroedinger equation for an atom interacting with a strong laser field. The timedependent wave function of a given valence electron is calculated on a spatial grid using a oneelectron pseudo potential. This single active electron approximation (SAE) was shown to be a good approximation for the rare gases at the intensities and wavelengths that we will consider. The SAE potential used has an explicit angular momentum dependence which allows us to reproduce all of the excited state energies for xenon quite well.
 Publication:

Presented at the 6th International Conference on Multiphoton Processes
 Pub Date:
 August 1993
 Bibcode:
 1993mupr.conf...25S
 Keywords:

 Energy Spectra;
 Populations;
 Pulse Duration;
 Pulsed Lasers;
 Schroedinger Equation;
 Trapping;
 Xenon;
 Electron Energy;
 Excitation;
 Ionization;
 Wave Functions;
 Lasers and Masers