The Study Of Lasing Without Inversion And Coherent Control Of Optical Properties In An Open Λ-Type Three-Level System

The study of coherent control of optical properties and optical courses is oneof the most important and active research front fields in international opticsnowadays. The study of coherent control has not only an important theoreticalvalue, but also wide application prospects in many fields, such as quantumoptics, nonlinear optics, quantum information and photo-communication, etc. Inaddition, atomic coherence and quantum interference effects have multiplepotential applications in many aspects. Among numerous phenomena of atomiccoherence and quantum interference, lasing without inversion (LWI) hasreceived tremendous attention. As a new method of producing laser, LWI canobtain laser light in spectral domains, e.g. the x-ray even γ-ray range, whereconventional methods based on population inversion are not available or aredifficult to implement, so the study of LWI has not only an important theoreticalvalue, but also wide application prospects.Based on the work of the former people, we studied the lasing withoutinversion and coherent control of optical properties in an open Λ -type systemin this paper. This paper consists of five chapters.In Chapter 1, we explained the significance for studying coherent controland LWI, showed the basic principle of producing LWI, and introduced simplythe current research state of coherent control and LWI, and the main contents forthe important study subject at present.In Chapter 2, we investigate a way resulting in lasing without inversion(LWI) in an open resonant Λ -type three-level system from a nonlineardynamics viewpoint. The destabilization of the non-lasing solution can occur notthrough Pitchfork bifurcation, giving rise to continuous wave LWI, but alsothrough Hopf bifurcation, giving rise to self-pulsing LWI. This is much differentfrom that of the corresponding closed resonant Λ -type three-level system inwhich the destabilization of the non-lasing solution can occur only throughPitchfork bifurcation. Moreover, we discussed the effect of the unsaturated gaincoefficient, cavity loss coefficient, ratio of the atomic injection rates and atomicexit rate on the two destabilizations that can lead to producing LWI.In Chapter 3, based on the work of chapter 2, using the numerical calculationresults, we have studied the transient evolution processes and steady outputs ofthe continuous LWI originating from Pitchfork bifurcation instability andself-pulsing LWI originating from Hopf bifurcation instability in a resonant openΛ-type three-level atomic system. We found that the two kinds of LWI havesome obvious differences not only from the steady outputs but also from thetransient evolution process. The effects of the unsaturated gain coefficient,cavity loss coefficient, ratio of the atomic injection rates and atomic exit rate onthe transient evolution processes and steady outputs are discussed.In Chapter 4, we have investigated the control role of the relative phasebetween the probe and driving fields on the probe gain, dispersion andpopulations in an open Λ -type system with spontaneously generated coherence(SGC). It is shown that by adjusting the value of the relative phase, a changefrom lasing with inversion to lasing without inversion can be realized;the valuesand frequency spectrum regions of the inversionless gain and dispersion can beobviously varied;high index of the refraction with zero absorption and theelectromagnetically induced transparency can be achieved. It is also found thatwhen the driving field is resonant, the shapes of the dispersion and the gaincurves versus the probe detuning are very similar if the relative phase of thedispersion lags π 2 than that of the gain, however for the off-resonant drivingfield the similarity will disappear;the gain, dispersion and populations areperiodical functions of the relative phase, the modulation period is always 2π;the contribution of SGC to the inversionless gain and dispersion is much largerthan that of the dynamically induced coherence.In Chapter 5, we have investigated the effects of the relative phase betweenthe probe and driving fields and other system parameters on the probe gain (orabsorption) and the group velocity of the probe light pulse (GVPLP) in an openΛ -type three-level system with the spontaneously generated coherence (SGC)when the weak probe field and the strong driving field have differentfrequencies. It is found that: adjusting the detuning or Rabi frequency of theprobe light field can realize the switching of the GVPLP from subluminal tosuperluminal. The absolut value of the GVPLP always increases with Rabifrequency of the driving light field increasing. Changing the relative phasebetween the probe and the driving lght fields or the atomic exit and injectionrates can lead to GVPLP varying in a wider range, without the incoherentpumping, the property of the GVPLP cannot transformed;with the incoherentpumping, the switching of GVPLP from subluminal to superluminal can berealized not only by adjusting values of the relative phase between the probe anddriving fields but also by varying values of the incoherent pumping rate.Without the incoherent pumping, for subluminal and superluminal propagation,the system always exhibits the probe absorption;with the incoherent pumping,for subluminal propagation the system always exhibits the probe absorption,however, the superluminal propagation is always companied with gain of theprobe field. And GVPLP is mainly determined by the slope of the steepdispersion.