The Study Of Lasing Without Inversion And Coherent Control Of Optical Properties And Propagation Of The Sub-cycle Pulse In An Λ-Type Three-level System

This paper represents mainly two aspects research: one is the study of lasing without inversion and coherent control in an inhomogeneous broadeningΛ-type three-level system; the other is to numerically solute the Maxwell-Bloch equations employing predictor-corrector finite-difference time-domain method, and simulate propagation of sub-cycle laser pulse in a denseΛ-type three-level system. This paper consists of eight chapters, and the main contents and results are illustrated as follows:In chapter 1, we explain the significance of the studying coherent control, LWI showed the basic principle of producing LWI, give the development and applications of ultrashort laser pulses, and introduce simply the current research state of coherent control, LWI and the interaction of the ultrashort laser pulse with medium.In chapter 2, we discuss the effect of the Doppler-broadening on the gain and the population difference. The result shows that regardless of the driving field being on resonance or not, for the counter- or co-propagating of the probe and driving fields (PDF), GWI does not monotonously decrease or increase with Doppler width increasing; except the case of the counter-propagating PDF with off-resonance driving field, at a suitable Doppler width one can get a gain maximum value much larger than that without Doppler broadening; especially in the situation of the resonant driving field, the co-propagating geometry leads to a more large GWI; in addition, for the counter-propagating geometry, when Doppler width is larger enough, GWI oscillation occurs, and the oscillation amplitude and region increase with Doppler width increasing. These conclusions are very different from that obtained in previous investigation (i.e. the gain monotonously decreases with Doppler width increasing). In chapter 3, based on the work of chapter 2, we firstly investigate the effect of the spontaneously generated coherence (SGC) on gain of lasing without inversion (LWI) in a closed three-levelΛ-type atomic system with Doppler broadening. It is shown that, regardless of the driving and probe fields being co- or counter–propagating, at a suitable value of the Doppler width, we can obtain a much larger LWI gain with SGC than that without SGC; and the region of the LWI gain spectrum with SGC is obviously larger than that without SGC. When the Doppler width takes a constant value, the gain does not monotonously decrease or increase with increasing of strength of SGC, the largest LWI gain can be obtained by adjusting strength SGC. Generally speaking, the co-propagating probe and driving fields is favorable to obtain a larger LWI gain.In chapter 4, for the first time, we studied the control role of the relative phase between the probe and driving fields on inversionless gain of the probe field in a closed and Doppler broadeningΛ-type three-level system with the spontaneously generated coherence (SGC). It is shown that:(1) Regardless of the driving field being on- or off- resonance, and regardless of the probe and driving fields being co- or counter- propagating, always the gain maximum value varies periodically with variation of the relative phase, the period is 2π. (2) When the driving field is on-resonance, the gain maximum value decreases monotonously with Doppler width increasing, moreover, the decreasing in the counter-propagation case is quicker than that in the co-propagation case; when the driving field is off-resonance, the gain maximum value does not monotonously decrease or increase with Doppler width increasing. For above both cases, the largest inversionless gain can be gotten by adjusting value of the relative phase. (3) The contribution of SGC to the inversionless gain is much larger than that of the dynamically induced coherence.In chapter 5, we derive Maxwell-Bloch equations beyond slowly varying envelope approximation (SVEA) and rotation-wave approximation (RWA) are located in chapter five, and simply elucidate the predictor-corrector finite-difference time-domain method.In chapter 6, by solving the full Maxwell-Bloch equations without SVEA and RWA, we numerically investigate the interaction of sub-cycle laser pulse and a denseΛ-type three-level atomic system. We find that the Rabi frequency and the populations in a dense medium are quite different from those in a dilute medium; the time derivative of the electric field has stronger effects on the time evolution of the pulse in the dense medium than that in a dilute medium, so the trailing and leading edge of the pulse occurs oscillations; for the larger pulse area, split of pulse occurs in a dense medium, and not occur in a dilute medium; the time of pulse appearing in a dense medium is later than that in the dilute medium; the larger is the area of the input pulse, the more evident is the difference. In addition, the time evolution rules of the carrier Rabi frequency in the two cases with and without LFC are much different in a dense medium; the amplitude of the main pulse is larger or smaller with LFC than that without LFC since the effect of the NDD interaction will enhanced or depresses the light-matter interaction; when the area of the input pulse is larger, split of pulse occurs, and the time interval between the two sub-pulses increase with propagation distance increasing and the time interval between the two sub-pulses in the case without LFC is longer than that with LFC; the time evolution rules of the populations of levels |1>, |2> and |3> in the two cases with and without LFC are much different in a dense medium; the larger is the area of the input pulse, the obviously evident are the effects of LFC on time evolutions of the pulse and populations.In chapter 7, we analyze spectrum of a sub-cycle laser pulse propagating in a denseΛ-type three-level atomic medium. It is found that regardless of in a dilute medium and in a dense medium, the spectrum is broaden due to the self-phase modulation (SPM); however, the width is much larger in the dense medium than that in a dilute medium because of NDD interaction. In the dense medium, the supercontinuum spectrum occurs due to SPM and NDD interaction, and the maximum frequency is 10ωp.In chapter 8, we investigate the propagating property of the two-color sub-cycle pulses in a denseΛ-type three-level atomic system, we find that the initial phase of the two-color pulse has the effect on the time evolution, and the pulse splitting in a dense medium is very different from those in a dilute medium.