Amplification without population inversion and enhancement of refractive index with zero absorption using two-photon pumping

Abstract

ABSTRACT The simple model is proposed for amplification of a probe optical radiation without popu- lation inversion and enhancement of refractive index at a point of vanishing absorption whena strong driving field is present at the adjacent two-photon transition. The conditions for observation of the effects have been determined. Keywords: atomic coherence, quantum interference, amplification without population inver- sion 1 .INTRODUCTION Considerable interest has been paid recently to the study of effects of an amplification with-out a population inversion (AWl) 1 and enhancement of refractive index at a point of vanishingabsorption of probe 2• AWl means amplification of a weak probe radiation by resonant atomicsystem in the absence of population inversion between the operating atomic levels. At the sametime it is supposed that the system can be driven by the external coherent fields and can contactwith reservoir. Many schemes for amplification and lasing without a population inversion havebeen proposed and the dependence of the optical gain on various system parameters has beenexamined. Among the proposed schemes, some are based on the quantum interference effectswhich result in different emission and absorption profiles in the atomic system; others dependon the utilization of external coherent fields that generate atomic coherence leading to opticalgain in the absence of population inversion. Several experimental studies of AWl in the opticalregion have been published recently We'd