We investigate the absorption spectrum of a laser-driven V system in which one of the upper levels is metastable. If the Rabi frequency of the laser driving the metastable transition is sufficiently small we find an extremely narrow peak in the stationary absorption spectrum of a weak probe on the strong transition. We give analytical expressions approximating the stationary absorption spectrum. The absorption spectrum of a two-level system is investigated for the case where an upper limit for the time separation of successive emissions is given. The absorption spectrum then exhibits a delta-function-like peak and using this we then show that the origin of the narrow peak in the absorption spectrum can be traced back to electron shelving, i.e. to the existence of light and dark periods in the resonance fluorescence emitted on the strong transition.
We investigate the absorption spectrum of a laser-driven V system in which one of the upper levels is metastable. If the Rabi frequency of the laser driving the metastable transition is sufficiently small we find an extremely narrow peak in the stationary absorption spectrum of a weak probe on the strong transition. We give analytical expressions approximating the stationary absorption spectrum. The absorption spectrum of a two-level system is investigated for the case where an upper limit for the time separation of successive emissions is given. The absorption spectrum then exhibits a delta-function-like peak and using this we then show that the origin of the narrow peak in the absorption spectrum can be traced back to electron shelving, i.e. to the existence of light and dark periods in the resonance fluorescence emitted on the strong transition.
We investigate the spectrum of resonance fluorescence of laser-driven three-level systems in the V or $\ensuremath{\Lambda}$ configuration where one transition is metastable. If the laser driving the weak transition has a sufficiently small Rabi frequency we find an extremely narrow structure in the resonance fluorescence spectrum of the strong transition. Analytical expressions approximating the spectrum are given and the properties of the spectrum are discussed. With the help of a simplified model of resonance fluorescence emitted on the strong transition we are able to show that the origin of the narrow peak can be traced back to electron shelving, i.e., to the existence of light and dark periods in the resonance fluorescence emitted on the strong transition.
We investigate time-dependent spectra of the intermittent resonance fluorescence of a single, laser-driven, three-level atom due to electron shelving. After a quasistationary state of the strong transition, a slow decay due to shelving leads to the steady state of the three-level system. The long-term stationary spectrum consists of a coherent peak, an incoherent Mollow-like structure, and a very narrow incoherent peak at the laser frequency. We find that in the ensemble-average dynamics, the narrow peak emerges during the slow decay regime, after the Mollow spectrum has stabilized but well before an average dark time has passed. The coherent peak, being a steady-state feature, is absent during the time evolution of the spectrum.
The temporal behavior of a single quantum system may contain information, for instance, about macroscopic dark periods in electron shelving, which is washed out or even lost in ensemble averages. The same is true in principle for spectral information. For example, for an atom with light and dark periods one might try to spectrally analyze the light emitted in a light period of given length or, more generally, the light emitted into one solid angle while monitoring the temporal emission in another solid angle. Considering different emission behaviors one may get different spectra, i.e., spectra that are dependent on the conditions imposed. In this paper, such questions, in particular the notion of spectrum in a light period, are studied. To this end we generalize the recent quantum jump approach to include resonance-fluorescence spectra of single atoms. We explicitly show that the theory developed in this paper easily generalizes, e.g., to absorption spectra. We apply the theory to a V system that has one metastable level and that may exhibit intermittent fluorescence when driven by two lasers. We show that the spectrum of resonance fluorescence of the complete ensemble differs substantially from that observed in a light period. A physical explanation of this behavior is presented. \textcopyright{} 1996 The American Physical Society.
We examine the absorption of a weak probe beam by a laser driven V-type atom with a pair of closely lying excited levels, where both the driving and probe lasers interact simultaneously with the two transitions. The effects of quantum interference among decay channels on the absorption spectra are also investigated. We introduce dipole moments in the dressed-state representation and the Hamiltonian in terms of the dressed states describing the interaction between the probe and the atom. In the degenerate case, features similar to that of a driven two-level atomic system are found due to some dark transitions in the spontaneous emission and the fact that the probe beam only detects certain transitions. In the nondegenerate case, the absorption spectrum is strongly influenced by the degree of quantum interference, resulting in different line shapes for emission peaks, absorption peaks, and dispersionlike profiles. The effect of probe polarization on the absorption spectrum is also investigated.
We investigate the steady-state spontaneous emission spectrum of a three-level atom driven by two coherent fields and the absorption spectrum of a weak probe passing through a collection of such driven atoms. We find that the fluorescence spectrum is strongly affected by the decay rates of all the levels involved in the atomic evolution and not just by the decay parameters of the specific transition whose emission spectrum is being monitored. In particular, the spectral components can acquire very different widths and peak heights relative to the case of the standard resonance fluorescence in which a two-level system is driven by a single near-resonant field. An external probe signal passing through the gas of three-level atoms may be absorbed or amplified, as in the standard two-level case, but under specific operating conditions, amplification (or absorption) occurs over the entire range where the atomic response is appreciable. In this case the existence of amplification or absorption is controlled solely by the population difference between two dressed states of the system. We provide numerical results in support of our arguments for arbitrary values of the atomic and field parameters and also develop an analytic description in the limit of strong driving fields that leads to explicit line-shape and linewidth formulas.
Abstract When a two-level system is driven on resonance by a strong incident field, its emission spectrum is characterized by the well-known Mollow triplet. If the absorption from the excited state, in this continuously driven two-level system, to a third, higher energy level, is probed by a weak field, the resulting absorption spectrum features the Autler-Townes doublet with two peaks separated by the Rabi frequency of the strong driving field. It has been shown that when the two-level system is instead driven by a periodic pulse sequence, the emission spectrum obtained has similarities with the Mollow triplet even though the system is only driven during the short application time of the pulses and is allowed to evolve freely between pulses. Here, we evaluate the absorption spectrum of the three-level system in the ladder/cascade configuration when the bottom two levels are driven by a periodic pulse sequence while the transition between the middle and the highest level is probed by a weak field. The absorption spectrum displays similarities with the Autler-Townes doublet with frequency separation between the main peaks defined by the inter-pulse delay. In addition, this spectrum shows little dependence on the pulse carrier frequency. These results demonstrate the capacity to modulate the absorption spectrum of a three-level system with experimentally achievable pulse protocols.