Coherent Interaction of Frequency-Modulated Laser Pulses with Rb Atoms

Abstract

We investigate the behavior of Rb85 atoms in the field of a sequence of frequency-chirped short laser pulses for coherent manipulation of the Rb atomic beam. The analysis is based on numerical solution of equations for the density matrix elements of the hyperfine levels of the 5S1/2-5P3/2 transition in Rb85 atom. We analyze two different regimes of interaction including relatively short laser pulses (when the width of the pulse envelope spectrum is of order or exceeds frequency interval between the hyperfine levels resulting in effective mixing of them) and relatively long ones (when the ground hyperfine levels are resolved but the excited ones are not resolved). We show that in all regimes considered, the interaction of a frequency-chirped laser pulse with the multilevel Rb85 system is similar to the interaction with an effective two-level atom at sufficiently large peak intensities of the pulses. It allows us to perform efficient excitation of the multilevel atom by transferring populations of two hyperfine ground states to the excited ones and back to the ground states using a pair of frequency-chirped laser pulses. We present experimental results of utilizing this scheme of population transfer for coherent manipulation of an ensemble of Rb85 atoms in a magneto-optical trap.