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Acta Physica Sinica

TIME EVOLUTION OF ATOMIC RESPONSE AND LIGHT AMPLIFICATION MECHANISM IN AN OPEN I NVERSIONLESS LASING SYSTEM

Fan Xi-jun, Shufen Tian, LI JIAN, 刘杰 Liu Jie, BAI CHENG-JIE, (1)山东师范大学传播学院，济南 250014; (2)山东师范大学物理系，济南 250014

Published Jan 1, 2000• 5 citations
Publisher

Abstract

We study the law of time evolution of atomic response in an open Λ-type inversi onless lasing system,elucidate the light amplification mechanism without inversi on,and find that the character of the time evolution of atomic response in an open system is obviously different from that in a corresponding closed system. Weconsider that the variation of the oscillation frequency and anharmonic oscillat ion in the process of time evolution originate from the stochastic coherence pro perty of atom oscillators in the system.

DOI
10.7498/aps.49.1719

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We study the law of time evolution of atomic response in an open Λ-type inversi onless lasing system,elucidate the light amplification mechanism without inversi on,and find that the character of the time evolution of atomic response in an open system is obviously different from that in a corresponding closed system. Weconsider that the variation of the oscillation frequency and anharmonic oscillat ion in the process of time evolution originate from the stochastic coherence pro perty of atom oscillators in the system.
We study the time evolution law of the atomic response in an open Λ type inversionless lasing system when the probe or driving field is off resonance,and compare the law with that obtained when the probe and driving fields are resonant.We find that the detuning has considerable effects on the time evolution law:When the probe or driving fields is off resonance,the dispersive responses for the probe and driving fields are no longer 0 and the two photon coherence is no longer a pure real;The variation of the probe detuning can make the time evolution law of the population distributions and the gain (absorbtion) of the driving field changing obviously;With detuning increasing,the time evolution behavior of the gain (absorbtion),dispersion of the probe field and the two photon coherence will gradually diviate from the evolution law of the standard damped oscillator;With the driving detuning increasing,the oscillating time of the dispersion of the driving field becomes longer,the amplitude and the stationary value increase.
The law of time evolution of atomic response in an open V type lasing without inversion (LWI) system with two incoherent pumps is investigated by the numerical results.Following conclusions are shown:the time evolution of the populations of the two levels coupled by the probe field has the same oscillation frequency,however,exists a phase difference π;the initial values of the populations affect mainly the oscillation amplitudes of the gain,coherent item and population difference but dont affect their values in the steady state;the ratio of the atomic injection rates increasing will results in an increase of the gain and a decrease of the population difference in the steady state;the atomic exit rate increasing will make both the gain and population difference in the steady state decreasing.
Under the conditions of the rotatingwave,slowly varying envelope approximations.It was found that Variation of the driving field Rabi frequency doesn′t vary the oscillation (or nonoscillation) characteristic of the atomic response time evolution and the time needed for reaching to steady state,but will vary size of the oscillation frequency and steady value;increase of incoherent pumping rate doesn′t vary the oscillation frequency and steady value,but will make oscillation times decreasing,oscillation amplitude reducing,time needed for reaching to steady value shorting,however,the steady value of each atomic response doesn′t increase or decrease monotonously with incoherent pumping rate increasing;variation of initial condition of the system doesn′t vary the law of time evolution of atomic response and the steady value of each atomic response.
We analyze transient properties of light amplification in a coherently coupled three-level \ensuremath{\Lambda}-type system and study the system evolution from the transient regime into the steady state. From the time evolution of the atomic coherence and population distribution, we discuss the transient light amplification mechanism with and without population inversion. We also solve the density-matrix equations in the steady state and derive the conditions for the existence of specific light amplification mechanisms, such as light amplification without inversion in any standard state basis, light amplification by stimulated Raman scattering, and light amplification from population inversion in the dressed states.
Begin with the density matrix equations of motion under the conditions of the rotating wave,slowly varying amplitude and mean field approximations,by using the numerical calculation results,the time evolution laws of the probe laser field and populations corresponding to two cases in producing inversionless lasing (i.e.,through the Pitchfork bifurcation giving rise to continuous wave lasing emission and through the Hopf bifurcation giving rise to self-pulsing lasing emission) in an open V-type resonant system are studied,and the effects of the system parameters varying on the time evolution laws are discussed.