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Chinese Physics Letters

Effects of Detunings on Dynamically Induced Irreversibility in Coherently Driven Systems

Xiangming Hu, Jin-sheng Peng

Published Mar 1, 2000• 7 citations
Publisher

Abstract

Effects of detunings on dynamically induced irreversibility is studied for coherently driven V systems in which there is no conventional source of irreversible population pumping. For atomic barium (γ 1 /γ 2 = 400 >> 1, where γ 1 and γ 2 are the rates of the spontaneous decay from the excited states 6 s 6 p 1 P 1 and 6 s 6 p 3 P 1 to the ground state 6 s 2 1 S 0 , respectively), the strong irreversibility is found to lead to a maximum inversion of 0.77 [only 0.1 in Phys. Rev. Lett. 71 (1993) 4311 ]. The maximum population inversion requires relatively strong fields coupled respectively to two transitions, a disparity in two atomic decay rates, and the atom-field detunings of opposite signs. However, it is also shown that even in the cases where two detunings have the same sign, or where two decay rates are equal, population inversion takes place.

DOI
10.1088/0256-307x/17/3/016

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Effects of detunings on dynamically induced irreversibility is studied for coherently driven V systems in which there is no conventional source of irreversible population pumping. For atomic barium (γ 1 /γ 2 = 400 >> 1, where γ 1 and γ 2 are the rates of the spontaneous decay from the excited states 6 s 6 p 1 P 1 and 6 s 6 p 3 P 1 to the ground state 6 s 2 1 S 0 , respectively), the strong irreversibility is found to lead to a maximum inversion of 0.77 [only 0.1 in Phys. Rev. Lett. 71 (1993) 4311 ]. The maximum population inversion requires relatively strong fields coupled respectively to two transitions, a disparity in two atomic decay rates, and the atom-field detunings of opposite signs. However, it is also shown that even in the cases where two detunings have the same sign, or where two decay rates are equal, population inversion takes place.
We show that continuous-wave, two colour excitation of three-level atoms opens new channels of irreversible population transfer between atomic levels. This process, which we describe as dynamically induced irreversibility, leads to unanticipated phenomena including the inversion of atomic transitions whose upper atomic level has no conventional source of irreversible population pumping. We also study the effect of excitation-field bandwidth on the gain exhibited by driven, three-level, V-type atomic systems. Gain, which may or may not be inversionless in the atomic-state basis, is produced through strong monochromatic driving of one atomic transition and weaker pumping of a coupled transition. It is found that monochromatic pumping frequently yields greater optical gain than incoherent (wide bandwidth) pumping. This is particularly true when system gain can be attributed to hidden inversions among the eigenstates (semi-classical dressed states) of the coupled atom+driving field quantum system. Last, we report the observation of continuous-wave lasing in a strongly driven barium cascade system and interpret its properties in terms of the models presented.
We present a theory of light amplification in a cavity based on irreversibility of coherent excitation. It is predicted that the irreversibility of coherent excitation leads to a new way of lasing which is different from lasing with and without inversion in the conventional sense. Lasing with dynamically induced inversion is possible in coherently driven systems in which there is no conventional source of irreversible population pumping. This laser displays two interesting and important features: the maximum gain with inversion is substantially greater than gain without inversion, and in spite of the presence of the inversion, the noise intensity is reduced below the shot-noise limit.
Quantum interference in a decaying three-level system of V type with degenerate upper levels driven by a single incoherent field is shown to lead to a coherent population-trapping state and more generally to a population-locked state. The latter is a state with half the population locked in two upper states regardless of the strength of incoherent pumping and decay rates. We reveal the mechanism by which half the population is pumped to the upper states no matter how weak is the incoherent pumping. Transient regimes of gain without inversion and inversion without gain are demonstrated. Quenching of spontaneous emission due to electron collisions is also discussed in support of the experiments and ideas of Suckewer and [Phys. Rev. Lett. 60, 1122 (1988)].
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.