Population trapping in nonstationary conditions

R. R. Jones, Douglass W. Schumacher, P. H. Bucksbaum

We have observed trapping of population in Rydberg states of atoms and ions exposed to intense laser radiation. The trapping occurs in nonstationary ``wave-packet'' superposition states, created, via ac Stark-shifted multiphoton resonances during the laser pulse. The formation of these highly excited bound states requires the nonresonant absorption of up to 20 or more photons; some of the ionic Rydberg states lie nearly 32 eV above the ionic ground state. All of the trapped states having binding energies much less than the photon energy but remain stable against ionization even when the multiphoton ionization probability of the atom is saturated.

Thomas Lindvall, Mikko Merimaa, Ilkka Juhani Tittonen

Olga Makarova, Sergey V. Prants

Novel coherent transient effects of population locking in driven three-level media are demonstrated theoretically. With the help of exact solutions of the evolution equation with the time-dependent Hamiltonian we `design' laser and rf fields to lock population under the conditions of nonstationary two- and tri-photon resonances.

Michihiko Sugawara

S. Swain

The authors consider population trapping in a three-level system which is driven by two applied fields of arbitrary intensity, frequency and bandwidth. An irreversible loss of population is allowed to take place from the common level. The conditions are investigated under which population trapping can occur when spontaneous emission and finite radiation bandwidths are allowed. For the lambda configuration with monochromatic lasers the authors find that increasing the spontaneous emission rate can increase the amount of population trapped in the system, whereas spontaneous emission destroys trapping in the ladder configuration. For the case of uncorrelated lasers, finite laser bandwidths destroy trapping for either configuration.

Wolfgang Maichen, Rainer Gaggl, Ferruccio Renzoni +4 more