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Quantum Optics Journal of the European Optical Society Part B

Atomic coherence effects within the sodium D1manifold. III. Lasing without inversion via population trapping

Gunasiri G. Padmabandu, Xingfu Li, Chang Su, Edward S. Fry, Dmitri E. Nikonov, Shi-Yao Zhu, Georg M. Meyer, Marlan O. Scully

Published Aug 1, 1994• 8 citations
Publisher

Abstract

Transient lasing without inversion has been experimentally demonstrated in sodium vapour. The principle of this atomic coherence effect can be well understood from the theory of a simple four-level system. The experimental results match with numerical simulations which take the complete hyperfine structure of the sodium D 1 line into account. The differences between our system and a Raman laser are discussed.

DOI
10.1088/0954-8998/6/4/005

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Continuous wave (cw) amplification and laser oscillation without population inversion have been observed for the first time in a $\ensuremath{\Lambda}$ scheme within the sodium ${D}_{1}$ line. This is also the first demonstration in which the lasing medium was an atomic beam; this is an approach which, in addition to elucidating the physics, lays a foundation for extensions into the ultraviolet. Calculations using realistic atomic structure were critical to the choice of experimental approach. Observations agree with full density-matrix calculations and clearly show there was no population inversion.

Physical Review Letters•Mar 18, 1996•269 citations
Transient lasing without inversion has been experimentally demonstrated in sodium vapour. The principle of this atomic coherence effect can be well understood from the theory of a simple four-level system. The experimental results match with numerical simulations which take the complete hyperfine structure of the sodium D 1 line into account. The differences between our system and a Raman laser are discussed.
Atomic coherence effects within the sodium D1{\mathit{D}}_{1}D1​ line are shown to lead to the suppression of optical pumping, to the switching of light on and off when the coherence effects are turned on and off, and especially to lasing without inversion.
For pt. I see ibid. p. 231, 1994. We consider optical pumping in the multilevel sodium D 1 manifold by several coherent light fields. Coherence between atomic states is taken into account by solving the complete density matrix equations. The manifestation of population trapping and the variation of transmitted light intensity are predicted numerically and verified experimentally for the sodium D 1 line. The influence of relaxation and Doppler broadening is elucidated. The interaction of a strong and a weak field is shown to create electromagnetically induced transparency.
Atomic coherence gives rise to a series of interesting phenomena in quantum optics.1 In this work we investigate coherence effects within the Na Dl 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 3S1/2 (F=1, 2) → 3P1/2 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 (3P1/2) 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.
Continuous wave (cw) amplification and laser oscillation without population inversion have been observed for the first time in a $\ensuremath{\Lambda}$ scheme within the sodium D1{D}_{1}D1​ line. This is also the first demonstration in which the lasing medium was an atomic beam; this is an approach which, in addition to elucidating the physics, lays a foundation for extensions into the ultraviolet. Calculations using realistic atomic structure were critical to the choice of experimental approach. Observations agree with full density-matrix calculations and clearly show there was no population inversion.