Abstract

Atomic coherence gives rise to a series of interesting phenomena in quantum optics.¹ In this work we investigate coherence effects within the Na D_l line, demonstrating coherent trapping and lasing without inversion, and study the dependence of these phenomena on buffer gas pressure. Two pump laser beams (I, and I₂) are tuned to the frequencies υ₁ and υ₂ that correspond to the 3S_1/2 (F=1, 2) → 3P_1/2 transition and are right circularly polarized. Pockels cells are used to turn on or/and off the beams within approximately one nanosecond. To demonstrate lasing without inversion, a weak pulse of left polarized light tuned to t)₂ was used to create a small population in the upper level (3P_1/2) and the amplification of I, was observed. We found a significant gain in the absence of population inversion, which was verified by a direct experimental observation. These results were observed as a function of buffer gas pressure. The atomic coherence effects are shown to disappear in the presence of a helium buffer gas at a pressure of ≈ 1 Torr; whereas, complete optical pumping is only achieved at helium buffer gas pressures >10 Torr.

© 1993 Optical Society of America