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Physical Review A

Role of inhomogeneous broadening in lasing without inversion in ladder systems

Gautam Vemuri, G. S. Agarwal

Published Feb 1, 1996• 55 citations
Publisher

Abstract

We study the effect of Doppler broadening on the inversionless gain that can be realized in a ladder configuration. The gain is calculated when the strong coherent pump and the weak probe are either copropagating or counterpropagating. The results indicate that the counterpropagating situation is the optimal one for obtaining maximum amplification, since for identical Doppler broadening, the counterpropagating geometry yields higher amplification than the copropagating geometry. The effect of Doppler broadening on electromagnetically induced transparency in the same atomic system is also briefly discussed. \textcopyright{} 1996 The American Physical Society.

DOI
10.1103/physreva.53.1060

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An analysis is made of the effect of Doppler broadening on the gain in an open ladder inversionless lasing system. It is shown that for co-propagating probe and driving fields, the gain does not monotonously decrease or increase with increasing Doppler width, and at a suitable Doppler width one can obtain a maximum value much larger than that without Doppler broadening. For counterpropagating probe and driving fields, when the Doppler width is large enough, gain oscillation occurs, and the oscillation amplitude and region increase with increasing Doppler width. This conclusion is very different from that obtained in the corresponding closed system.
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We study the response of an inhomogeneously broadened atomic three-level ladder system to a strong probe beam under conditions in which electromagnetically induced transparency would be induced on a weak probe beam. Theoretical analysis and experimental data show that saturation effects associated with the strong probe can substantially alter the behavior of the system and can result in enhanced probe absorption under exactly the same circumstances in which a weak probe would experience enhanced transparency. Strong probe effects are also shown to lead to a breakdown of the correspondence between population inversion and gain. A power-series solution of the density-matrix equations describing the ladder system provides a physical picture for strong probe effects in terms of interfering multiphoton transition pathways.