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Physical Review A

Lasing without inversion in a closed three-level system

Yifu Zhu

Published May 1, 1992• 126 citations
Publisher

Abstract

It is shown that a closed V-type, three-level system, which is incoherently pumped on the transition at which lasing occurs and coherently pumped on the other transition, exhibits lasing without population inversion in any atomic state basis. The same system can be also made to exhibit lasing without population inversion in the bare atomic state basis but with population inversion in the dressed-state basis.

DOI
10.1103/physreva.45.r6149

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EXTERNAL-FIELD-INDUCED COHERENCE AND LASING WITHOUT INVERSION: THE V-TYPE SYSTEM

Zhenfei Luo, Zhizhan Xu, 中国科学院上海光学精密机械研究所,上海201800

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Acta Physica Sinica•Jan 1, 1993•0 citations
It is shown that a closed V-type, three-level system, which is incoherently pumped on the transition at which lasing occurs and coherently pumped on the other transition, exhibits lasing without population inversion in any atomic state basis. The same system can be also made to exhibit lasing without population inversion in the bare atomic state basis but with population inversion in the dressed-state basis.
We show that a closed four-level system can exhibit lasing without population inversion in any state basis. The same system can be also made to exhibit lasing without population inversion in the bare-state basis but with population inversion in the dressed-state basis. We derive the conditions of lasing without inversion and examine the dependence of the gain on various system parameters. The lasing threshold and the steady-state photon numbers are calculated. Comparison with a ssV-type, three-level model is presented.
We show lasing without population inversion in a closed four-level atomic system which is no longer incoherently pumped on the transition at which lasing occurs. The four-level system can overcome some limits in the typical lambda-type and V-type three-level systems, furthermore it is possible to achieve lasing even in the absence of the inversion condition for the thermal radiation fields or of the inversion of spontaneous decay rate. We find that when the detuning of probe field is equal to that of coherent coupling field, there is a peak value along with the increase of the detuning. To explain it, we bring forward that there are adiabatic and nonadiabatic stimulated Raman processes when a three-level atomic system is interacted with two coherent fields, so there are two mechanisms influencing the change of probe field. We believe that it can explain more general lasing without inversion processes because of quantum interference induced by coherent fields.
We analyze transient properties of light amplification without population inversion (LWI) in a closed three-level @sV -type system and study the system evolution from transient LWI into steady-state LWI. From the time evolution of the atomic coherence and population distribution with and without an incoherent pump field, we elucidate the light amplification mechanism and derive the conditions under which the @sV system exhibits LWI in any state basis. We derive analytical solution for the steady-state LWI and discuss other mechanisms of light amplification such as stimulated Raman scattering and population inversion in the dressed states. \textcopyright{} 1996 The American Physical Society.
We have studied an incoherently pumped laser operating with a Doppler-broadened three-level system placed in a doubly resonant cavity. This system generates two laser fields, one of them without population inversion. Both ladder and V-type three-level schemes are considered with a ratio $R={\ensuremath{\omega}}_{\ensuremath{\alpha}}/{\ensuremath{\omega}}_{\ensuremath{\beta}}$ of inversionless laser frequency ${\ensuremath{\omega}}_{\ensuremath{\alpha}}$ to ordinary laser frequency ${\ensuremath{\omega}}_{\ensuremath{\beta}}$ of R=0.67R=0.67R=0.67 and R=1.88,R=1.88,R=1.88, respectively. Dual-wavelength lasing extends up to Doppler-broadening values for optical transitions of atoms in a vapor cell. Some considerations for the practical realization of this dual-wavelength laser are discussed.