Introduction

We have been investigating coherence and interference effects in three level atoms which are probed on one transition while subject to a strong, resonant drive field on another. In a typical experiment, the probe absorption, or phase shift, is measured as the probe is scanned over the atomic resonance. Since both the drive and probe are close to resonace, many different quantum mechanical paths can contribute to the observed probe gain or loss: the single photon linear probe absorption interferes with multi-photon processes involving one probe photon and two or more drive photons. This interference can give rise to many interesting effects including gain and lasing without population inversion (GWI,LWI) and an anomalously large index of refraction with vanishing absorption coefficient. Among potential applications are the generation of short-wavelength coherent radiation, ultra-sensitive magnetometers and sub-Doppler laser cooling of atoms.

At NIST we have examined several aspects of this area. In 1995, we produced the first experimental demonstration of LWI in a room temperature vapor of Rb⁸⁷ atoms (A. S. Zibrov, et al., Phys. Rev. Lett., 75, 1499, 1995). In this experiment, atoms were driven strongly on the D2 line at 780 nm while being probed on the D1 line with a laser at 795 nm. With a suitably applied repump laser, optical gain without population inversion was observed on the probe transition. This experiment was repeated in a sample of laser cooled atoms confined in a magneto-optic trap (J. Kitching and L. Hollberg, in press, Physical Review A).

Further Information:

• Coherence effects in Doppler broadened media
• Coherence effects in a sample of cold, trapped atoms

References:

M.D. Lukin, M. Fleischhauer, A.S. Zibrov, H.G. Robinson, V.L. Velichansky, "Spectroscopy in Dense Coherent Media: Line Narrowing and Interference Effects", Phys. Rev. Lett., 79, 2959-2962, 1997.

A.S. Zibrov, M.D. Lukin, L. Hollberg, D.E. Nikonov, M. O. Scully, H.G. Robinson, and V.L. Velichansky, "Experimental Demonstration of Enhanced Index of Refraction via Quantum Coherence in Rb", Phys. Rev. Lett., 76, 3935-3938, 1996.

A.S. Zibrov, H.G. Robinson, V.L. Velichansky, V.V. Vasiliev, L. Hollberg, E. Arimondo, M.D. Lukin, and M.O. Scully, "Population- and Coherence-Induced Gain and Self-Oscillations in Alkali Vapor", Proc. Fifth Symp. on Frequency Standards and Metrology, ed. J.C. Bergquist, World Scientific, 490-492, 1995.

A.S. Zibrov, M.D. Lukin, D.E. Nikonov, L. Hollberg, M.O. Scully, V.L. Velichansky, and H.G. Robinson, "Experimental Demonstration of Laser Oscillation without Population Inversion via Quantum Interference in Rb", Phys. Rev. Lett., 75, 1499-502, 1995.