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Acta Sinica Quantum Optica

Effects of Laser Field Linewidth on Electromagnetically Induced Absorption

Xiao Shao-wu

Published Jan 1, 2008• 0 citations
OpenAlex

Abstract

Using matrix equation,we have calculated the absorpion of the prople field in the four-level atomic system in which three transitions are in N configuration under introducing laser field linewidth.We have done researches on the effects of laser field linewidth on electromagnetically induced absorption.The results indicate that atomic coherence of the four-level atomic system will be abated when the laser field linewidth is build up and laser field linewidth inhibits electromagnetically induced absorption.

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Acta Sinica Quantum Optica•Jan 1, 2012•0 citations
Using matrix equation,we have calculated the absorpion of the prople field in the four-level atomic system in which three transitions are in N configuration under introducing laser field linewidth.We have done researches on the effects of laser field linewidth on electromagnetically induced absorption.The results indicate that atomic coherence of the four-level atomic system will be abated when the laser field linewidth is build up and laser field linewidth inhibits electromagnetically induced absorption.
In this paper, we have calculated the absorption of the probing field in a N-type four-level atomic system with three dipole transitions using density matrix equation. The results indicate that the absorption or amplification of the probing field depends on the Rabi phases of the control field and signal field under introducing laser field Rabi phase, and the absorption or amplification periodically changes with the Rabi phases of the control field and the signal field at a period of 2π. The Rabi phase change of the probe field has no effect on the absorption. In addition, the effect of the signal field Rabi phase on absorption is the same as that of the control field Rabi phase on absorption. Rabi phase has an effect mainly on atomic coherence but little on atomic population.
Using density matrix equation,influence of the absorption(gain)of the probing field and diffraction efficiency of phase grating in a doubly degenerate four-level atomic system was calculated,under introducing laser field linewidth and intensities,and the variance of the probing field frequency and the variance of the ratio of coupling and probing field intensities,respectively.The results indicated that the increases of coupling field linewidth abates the atomic coherence in four-level system.When without considering(R=0)the coupling field linewidth,the gain and diffraction efficiency are larger than them when considering(R≠0)the coupling field linewidth.We found that the first-order diffraction efficiency of phase grating can reach up to 35%,when variance of the ratio of coupling and probing field intensitiesΩc/Ωp≈400.
The optical Bloch equations of a four-level atomic system with three closely spaced upper levels irradiated by a single mode of the electromagnetic radiation field are constructed. Under the rotating wave approximation and by using the slowly varying envelope approximation, we obtain the analytical solution to these optical Bloch equations. These solutions, which are obtained perturbatively, are used to calculate the polarization and hence the absorptive line shape. In particular, we examine the effects of the field-induced coherence arising from the interference between the probability amplitudes of the levels participating in dipole-allowed transitions. We obtain the shifts of the resonance peak positions due to two different reasons. The first is due to the nonlinear effects arising from the closely spaced nature of the peaks. The second is attributed to the field-induced coherence alone. It is found that the shifts of the positions of the resonance peaks due to field-induced coherence may be in the blue or in the red region.
In this paper we reveal that the constructive interference of atomic coherence on absorption leads to electromagnetically induced absorption,which is in sharp contrast to the case in which destructive interference of atomic coherence gives rise to electromagnetically induced transparency. A four-level atomic system is employed in which three transitions are in N configuration and the middle transition is used as a probe transition. In the dressed states representation the probe transition is split into four transitions that are coupled to each other. The coupling originates from the spontaneous emission of the atomic medium and the spontaneous transfer from excited state coherence to ground state coherence. The former leads to couplings between all transitions with the same sign and to the absorption reduction. The latter results in couplings,of which t wo terms have positive sign and another two have negative sign. It is due to the couplings with positive and negative signs that significant modification of the contribution of dressed coherence to absorption occurs,i.e., absorption inhibition is changed to absorption enhancement.
This paper investigates the effects of spontaneously generated coherence(SGC) on the probe absorption in the Y-type four-level atomic system driven by three fields.It finds that the probe absorption at the resonance center shows the different phenomena with the SGC effects.When SGC produces the destructive interference on the probe absorption,the absorption at the resonance center is reduced with the SGC enhancement and the gain appears there.When SGC produces the constructive interference on the probe absorption,the absorption at the resonance center is enhanced with the SGC enhancement.That is electromagnetically induced absorption(being abbreviated EIA);the intensity of double electromagnetically induced transparency(being abbreviated EIT);at both sides of the resonance is increased,and the windows get wider.At the same time,the linewidth of the absorption at the resonance center becomes narrow and the transparent windows at both sides of the resonance get wider when the spontaneous decay rate of energy levels |3〉→|2〉 and 4〉→|2〉 is decreased at the ratio of the spontaneous decay rate of energy levels |3〉→|2〉 and |4〉→|2〉 being constant.