Effects In Resonance Fluorescence Research Articles

Phase Dependence of Fluorescence Spectrum of a Two-Level Atomin a Trichromatic Field

We examine the phase-dependent effects in resonance fluorescence of atwo-level atom driven by a trichromatic modulated field. It is shownthat the fluorescence spectrum depends crucially on the sum of relativephases of the sideband components compared to the central component, notsimply on the respective phases. The appearance or disappearance of thecentral peak and the selective elimination of the sideband peaks areachieved simply by varying the sum phase. Once the sum phase is fixed,the spectrum keeps its features unchanged regardless of the respectiverelative phases.

Quantum interference effects in resonance fluorescence and absorption spectra of a V-type three-level atom damped by a broadband squeezed vacuum

The resonance fluorescence spectrum (RFS) and the absorption of a weak probe beam of a V-type three-level atom damped by a broadband squeezed vacuum and driven by a single coherent field which simultaneously couples the two upper states are studied. We consider the interplay between the squeezed field and the vacuum-induced coherence (VIC) between the two possible decay channels. The RFS for a degenerate excited doublet exhibits a high narrowing of the central line. In the situation in which the excited doublet is non-degenerate, we found that the squeezed field breaks the trapping condition attained when induced interference is maximal. A explanation of the main features in terms of dressed atomic states is given. We have also studied the probe absorption spectrum for a resonant driving field. It is shown that the probe may be amplified or absorbed over a wide range of frequencies when both quantum interference and the squeezed vacuum are considered. The sensitivity of the spectrum to the squeezed phase allows the control of the amplification/absorption of the probe signal.

Continuous photodetection of resonance fluorescence

The concept of photodetection as a continuous quantum measurement introduced by Srinivas and Davies is extended to the detection of resonance fluorescence. This is a new approach to an old subject. This is also a new development in continuous photodetection in the sense that a fermion rather than the traditional boson field is the subject of monitoring. The superoperators for the no-count and the one-count processes are postulated, following the examples of Srinivas and Davies. The probability for the m-count process is then derived on the basis of these postulates. The first two factorial moments of the photon-number distribution are calculated, which are then used to evaluate the non-classical effects in resonance fluorescence. A parameter slightly different from Mandel's is found to be more suitable indicator of photon antibunching in the transient state.

Nonclassical effects in resonance fluorescence from optical molasses.

Nonclassical effects in resonance fluorescence from optical molasses.

Coherent interatomic interaction and cooperative effects in resonance fluorescence

The influence of interatomic interactions on the coherently emitted transient in resonance fluorescence from a condensed-matter sample of identical two-level atoms is studied for the ultratransient regime. A closed solution of the modified Bloch equations is given. Temporal and spectral properties of the coherently emitted light as well as chirping are discussed.

Modeling of the optical piston: Density-wave shape and resonance-fluorescence effects.

We present results of a numerical model of the optical piston driven by laser-induced drift (LID). The model is based on a drift-velocity formulation of Lawandy, derived from an asymmetric-random-walk argument, and includes resonance-fluorescence effects. The model is applied primarily to the experimental conditions of H. G. C. Werij and co-workers (Phys. Rev. A 33, 3270 (1986)). It is shown that both the velocity and the shape of the propagating density wave change continuously throughout the traverse of a (finite) diffusion tube under these conditions. In addition, we have numerically verified the contention of G. Nienhuis (Phys. Rev. A 31, 1636 (1985)) that a ''self-preserving'' form of the density wave is indeed possible for the case of a ''finite number of absorbers in an infinite medium,'' both with and without saturation. Finally, we show that resonance fluorescence slows the piston velocity, broadens the density distribution, and decreases its peak height. It is concluded that resonance fluorescence can play a significant role in determining the time evolution and detailed shape of the optical-piston density distribution in sodium.

Nonlinear and stimulated effects in resonance fluorescence of one and two atoms

The Stark representation of the resonator field and the first order of perturbation theory of the fluorescence field are used to study the fluorescence spectrum of one and two two-level atoms in an ideal resonator as a function of the initial excitation of the system. It is shown that in the absence of resonator photons (nc = 0) the spectrum obtained for initial excitation of one atom consists of two lines located symmetrically relative to the central frequency ωα. In all other cases the spectrum consists of the central harmonic ωα and of ωα ± 2Ω satellites (Ω is the Rabi frequency). The intensity of collective higher harmonics ωα ± 4Ω is low and it falls on increase in the resonator field as I/nc2. The nonlinearity of the interaction Hamiltonian results in parametric amplification of the ωα + 2Ω harmonics and in attenuation of the ωα–2Ω harmonics. In the case of two atoms it is possible to achieve stimulated fluorescence at the harmonics ωα ± 2Ω.

Nonlinear and Stimulated Effects in Resonance Fluorescence of One and Two Two-level Atoms

The resonance fluorescence spectrum of one and two two-level atoms in an ideal cavity with one resonant mode is investigated as a function of the initial excitation of the system. The analysis is carried out in the Stark representation with respect to the cavity's field and in first-order perturbation theory with respect to the fluorescence field. In the absence of the field of the cavity (n c = 0) and under an initial excitation of one atom only, the spectrum consists of two lines which are symmetrical with respect to ωa. In all other cases the spectrum has a central line at ωa and other lines at ωa ± 2 Ω. The intensity of the higher (ωa ± 4 Ω) harmonics is small and decreases as 1/ 2 c c with increasing n>c. The nonlinearity of the interaction hamiltonian results in the parametric (with respect to the field of the cavity) amplification of the ωa + 2 Ω harmonic and the attenuation of the ωa − 2 Ω harmonic. The stimulated emission of the ωa ± 2 Ω harmonics, vanishing in a strong (n c » 1) field, is shown ...

Thermal reservoir effects in resonance fluorescence

The authors investigate the resonance fluorescence of a single coherently driven atom in the presence of an additional incoherent field. The analysis is based on a master equation describing the driven atom coupled to a reservoir and the incoherent field may be the black-body field associated with the finite temperature of the reservoir. The incoherent field induces asymmetries in the usual three-peaked Stark spectrum and these are compared with asymmetries derived from other models-notably the 'laser diffusion' model, and a more fundamental analysis. The theory is extended to the case of two or more atoms; the additional side bands (dips) in the fluorescence (absorption) spectrum occurring at higher harmonics of the laser Rabi frequency are also affected by the thermal field.

Antibunching, sub-poissonian photon statistics and finite bandwidth effects in resonance fluorescence

It is demonstrated that, although the fluorescent photons from a driven two-level atom always exhibit antibunching, they need not obey sub-poissonian statistics. The maximum sub-poissonian excursion of the normalized second factorial moment (〈(Δ n) 2〉 − 〈 n〉)/〈 n〉 occurs in the transient regime where it can approach the value -1. Effect s of finite bandwidth of excitation on photon statistics are also investigated and it is shown that the photon number distribution may be narrower with finite bandwidth excitation than with coherent excitation.

Collective atomic effects in resonance fluorescence: The "scaling factor"

Collective atomic effects in resonance fluorescence: The "scaling factor"

Erratum: Laser line-shape effects in resonance fluorescence

Erratum: Laser line-shape effects in resonance fluorescence

Laser line-shape effects in resonance fluorescence

The effects of different laser line shapes on the intensity and spectrum of resonance fluorescence from a two-level atom are investigated. The laser model considered is that of an ideal single-mode laser operating high above threshold, with constant amplitude and undergoing phase-frequency fluctuations analogous to Brownian motion. As the correlation time of the frequency fluctuations increases from zero to infinity, the laser line shape changes from Lorentzian to Gaussian in a continuous way. It is shown that for intermediate and strong fields, the average intensity of fluorescence in the case of a resonant broadband Lorentzian line shape is higher than that in the case of a Gaussian line shape with the same bandwidth and total power. This is in contrast to the weak-field case where the higher peak power of the Gaussian line shape makes it more effective than the Lorentzian line shape. It is also shown that in the case of a nonzero frequency correlation time (non-Lorentzian line shape) the intensity of fluorescence undergoes non-Markovian fluctuations. In relation to the spectrum of resonance fluorescence, it is shown that as the line shape is varied from Lorentzian to Gaussian the following changes take place: In the case of off-resonance excitation, the asymmetry of the spectrum decreases. In the case of resonant excitation, the center-peak to side-peak height ratio for the triplet structure increases. Moreover, the recently predicted center-line dip, which develops in the spectrum in the case of broadband excitation when the Rabi frequency and the bandwidth are nearly equal, becomes increasingly deeper.

Resonance fluorescence in a weak radiation field with arbitrary spectral distribution

Abstract : The authors show that the laser bandwidth effects in resonance fluorescence at low intensities can be treated most readily in terms of simple convolutions, and further that this approach allows one to consider an incident field with an arbitrary spectral distribution, with or without the presence of atomic (line-brroadening) collisions.

Evidence for vibrational mode-selectivity in the radiationless relaxation of a large molecule

Abstract Resonance fluorescence effects are absent in the two-photon-excited upper state fluorescence spectra of a centrosymmetric aromatic hydrocarbon. Spectra of states populated by radiationless relaxation are structured and sensitive to the excitation conditions. The results are interpreted in terms of vibration mode-selectivity of the internal conversion process between two highly excited singlet states.

Collective atomic effects in resonance fluorescence: Dipole-dipole interaction

The resonance fluorescence of a two-atom system interacting collectively with an intense driving field is studied. The first-order dispersion forces, or dipole-dipole interaction, between the atoms is included as well. The scattered-light spectrum is found to differ considerably from the single-atom spectrum even for very intense driving fields, in direct contrast with the results obtained by Agarwal et al., who studied the two-atom system but neglected the dipole-dipole interaction. The effects of collective scattering are calculated on the fluorescence spectra of idealized beams of atoms moving with uniform velocity, for a number of different number densities $〈N〉$.

Multiatom effects in resonance fluorescence

The intensity spectrum of the scattered radiation in two-atom resonance fluorescence is investigated and compared with the one-atom spectrum. For intense fields the spectra are found to be proportional to one another. A conjecture is made for the $N$-atom spectrum.

Optical bistability and cooperative effects in resonance fluorescence

We discuss a mean-field quantum-mechanical model which describes the dynamics of a homogeneously broadened system of two-level atoms contained in a pencil-shaped resonant cavity and driven by a coherent resonant field ${E}_{I}$. The model is treated in the semiclassical approximation. The model is justified on the basis of Maxwell-Bloch equations with two coherently coupled directions of propagation, with boundary conditions for the fields taken into account. Above a suitable critical density of atoms the system exhibits a bistable behavior including both the stationary situation and the transient, both the light transmitted in the forward direction and the fluorescent light. Bistability is shown to be a consequence of atomic cooperation. We give a simple description of optical bistability leading to new predictions for the transient behavior of the transmitted light and for the spectrum of the fluorescent light. The damping constant which characterizes the rate of appraoch to the stationary situation exhibits a hysteresis cycle. In the low-transmission regime the approach is monotonic, whereas in the highly transmitting situation the approach is oscillatory. One finds a critical slowing down in correspondence with the values ${{E}_{I}}^{(+)}$, ${{E}_{I}}^{(\ensuremath{-})}$ of the incident field where the transmitted field (as well as the total fluorescence intensity, the rate of approach to the stationary state, etc.) changes discontinuously. On the basis of the regression hypothesis we give a qualitative description of the spectrum of the fluorescent light. This is shown to undergo hysteresis and discontinuous changes at the same values ${E}_{I}^{(+)}$, ${E}_{I}^{(\ensuremath{-})}$ of the incident field. Below the critical density of atoms one recovers the usual picture of resonance fluorescence, with a continuous transition from a single-line spectrum to a three-peaked structure when the Rabi frequency becomes equal to the natural linewidth. Above the critical density the triplet appears only when the Rabi frequency becomes equal to the cooperative linewidth of pure super-fluorescence (i.e., for ${E}_{I}={E}_{I}^{(+)}$). Moreover, it appears discontinuously: when ${E}_{I}$ crosses the value ${E}_{I}^{(+)}$ the spectrum changes from a single narrow line to a triplet with well-separated sidebands.

Collective atomic effects in resonance fluorescence

We suggest that the statistical properties of the scattered radiation in resonance-fluorescence experiments may be affected significantly by the existence of atomic correlations. The scattered light spectrum from two- and three-atom collective systems has been calculated and compared with the one-atom spectrum. The differences are quite significant for weak fields, but become less pronounced as the intensity of the driving field is increased. In addition, we have calculated the scattered intensity correlation function for collectively interacting systems, and found that its behavior is very different from that of the single-atom intensity correlation function, both for weak and strong incident fields. The implications of our findings for the observation of photon antibunching are also discussed.

Multiple spontaneous emissions and interference effects in resonance fluorescence

A QED calculation of the resonance fluorescence spectra of a two-level atom in a strong, nearly resonant field, is reported, taking into account multiple spontaneous emissions (in any order) and interference effects. The results of this calculation are compared with the results of the quantum statistical theories, and the role of the elementary processes analysed. At resonance, in the high-field limit, the exact agreement of the QED and statistical theories is demonstrated. It is pointed out that the interference effects are of the greatest importance.