Abstract

A general, analytic theory is presented of the excitation of a two-level atom by a series of short optical laser pulses. The atom is assumed to be isolated (collisionless) with radiative decay from upper to lower state at rate γ. The laser pulses are assumed to have a duration t_p such that γt_p ≪ 1 (the transient regime), and the spacing between pulses t_r is such that t_r ≫ t_p. In this regime the atomic density matrix is calculated as a function of time during each optical pulse. An analytic expression for the atomic state (Bloch vector) after n optical pulses is also derived. For large n the atomic state converges to a repeating (steady state) cycle of pump excitation followed by radiative decay. The excited-state population in the steady state can be large but only if the spacing between pulses t_r is small so that γt_r ≲ 0.5. These results indicate that lasers that produce trains of pulses, such as mode-locked conventional lasers and free-electron lasers, can be effective in optical pumping of atoms.

© 1993 Optical Society of America

Absorption spectra of pulse-train-excited sodium two-level atoms

E. Krüger
J. Opt. Soc. Am. B 12(1) 15-24 (1995)

Pulse-train excitation of sodium for use as a synthetic beacon

Lee C. Bradley
J. Opt. Soc. Am. B 9(10) 1931-1944 (1992)

Theory of mesospheric sodium fluorescence excited by pulse trains

P. W. Milonni and L. E. Thode
Appl. Opt. 31(6) 785-800 (1992)

Response of a two-level atom to a frequency-modulated optically coherent pulse train

James M. Supplee, Edward A. Whittaker, and Keith Andrew
J. Opt. Soc. Am. B 15(7) 1833-1838 (1998)

Resonant radiation of an atom in laser pulse train

Weiping Zhang and Weihan Tan
J. Opt. Soc. Am. B 4(11) 1885-1892 (1987)