We study the effect of Doppler broadening on the inversionless gain that can be realized in a ladder configuration. The gain is calculated when the strong coherent pump and the weak probe are either copropagating or counterpropagating. The results indicate that the counterpropagating situation is the optimal one for obtaining maximum amplification, since for identical Doppler broadening, the counterpropagating geometry yields higher amplification than the copropagating geometry. The effect of Doppler broadening on electromagnetically induced transparency in the same atomic system is also briefly discussed. © 1996 The American Physical Society.

We analyze intensity and statistical properties of lasers without population inversion in a closed three-level V-type system. We derive the threshold condition and examine the intensity dependence on various system parameters. Unlike other inversionless laser systems that generate amplitude-squeezed light, the intensity fluctuation of the inversionless laser from the three-level V-type system is above the shot-noise limit in a wide parameter range studied here. © 1996 The American Physical Society.

The nonlinear analysis of the model equation for the single-feedback-mirror device with rubidium atoms predicts that a stable quasipattern of eightfold orientational order occurs in the profile of the output light beam. This pattern is numerically reproduced for different transverse shapes, either rhombohedric or circular, of the input beam. © 1996 The American Physical Society.

Degenerate four-wave mixing using broadband, non-transform-limited (incoherent) laser light having a Lorentzian spectral density is treated analytically for a Bloch two-level system. We consider the configuration in which an incoherent beam from a Lorentzian source is split into two beams having distinct k vectors, k and ${\mathit{k}}^{\prime }$. The twin beam along ${\mathit{k}}^{\prime }$ has been subjected to a controllable delay, τ, relative to k. These twin beams, focused into the sample of interest, generate new fourth fields, the signal at ${\mathit{k}}_{\mathit{s}}$=2k-${\mathit{k}}^{\prime }$ being examined here as a function of τ. A set of factorized time correlation (FTC) diagrams is introduced to organize the calculation and to yield both analytic expressions as well as physical insight. Not only is the signal not symmetric in τ but the signal can peak at τ≠0 even in the absence of inhomogeneous broadening. Finally, the physical insights and the use of the FTC diagrams are extended to rationalize several other incoherent light spectroscopies. © 1996 The American Physical Society.

The evolution of a quadrature-squeezed state through a Kerr medium is studied from the point of view of amplitude squeezing. We propose a Mach-Zehnder interferometer configuration, which incorporates a squeeze- state generator and a nonlinear Kerr medium, to generate and subsequently displace these states. The displaced states show amplitude squeezing for a proper choice of the initial quadrature squeezed state, and we study two such cases here in detail. In the limit where the evolution through a Kerr medium results in a macroscopic superposition, an initial phase-squeezed coherent state shows significant amplitude squeezing, and we have shown that the photon-number uncertainty 〈(Δn^${)}^2$〉 can be minimized to a value smaller than 〈n^${\mathrm{〉}}^{2/3}$. On the other hand, an initial quadrature-squeezed state, whose direction of squeezing is along the direction of excitation, upon evolving through a Kerr medium for a suitable small duration of time shows substantial amplitude squeezing for an appropriate displacement, and we show that the photon-number uncertainty in this case can be minimized to 〈n^${\mathrm{〉}}^{1/5}$, which is far below the previously achieved limits. © 1996 The American Physical Society.

We study theoretically resonance absorption of γ rays by nuclei exposed to an external radio-frequency (rf) magnetic field. The external field is taken to couple directly to the nuclear magnetic moments. Perturbation theory is developed for Mössbauer spectroscopy in terms of Floquet eigenstates that incorporate the rf field exactly. The present treatment allows for calculation of the conventional time-averaged absorption spectrum, as well as analysis of the time dependence of absorption, resolved on the scale of a period of the rf field. An efficient numerical implementation of the theory is described and comparisons with the equally general approach of Salkola and Stenholm [M. Salkola and S. Stenholm, Phys. Rev. A 41, 3838 (1990)] are made. We demonstrate that even at off-resonance frequencies a strong modulation leads to shifts of the original static hyperfine lines. Examples of line splittings of NMR’s associated with Rabi flopping are also shown. © 1996 The American Physical Society.

We derive a general expression for the linewidth of inhomogeneously broadened traveling-wave gas lasers, without any assumption on the relative magnitude of the atomic and field decay constants, and for several types of atomic pumping statistics, ranging from Poissonian to regular. For small inhomogeneous broadening, an important linewidth narrowing occurs in the bad-cavity limit. This effect disappears, however, in the large inhomogeneous broadening limit (Doppler limit). © 1996 The American Physical Society.

We present a general formalism for studying the cavity quantum electrodynamics for an atom or a radiating dipole inside a hollow spherical cavity. The atomic-energy-level shifts and the modified dipolar decay rates are calculated in specific cases. In particular, the energy shifts for an atom located at the center of an empty sphere (radius a) vary as 1/${\mathit{a}}^4$ for large ka and 1/${\mathit{a}}^2$ for small ka, where k is the wave number. We attribute these variations to the retarded Casimir-Polder interaction and the state-independent vacuum-field contribution, respectively. © 1996 The American Physical Society.

A theory of selective reflection (SR) of a light beam from the interface of a dielectric medium and a dense atomic vapor is presented. Following another earlier work on this subject [J. Guo et al., Opt. Commun. 110, 732 (1994)], we calculate the atomic density matrix and the transmitted field in the vapor self-consistently. We extend our previous theory to include an attractive atom-dielectric wall interaction and multiple atomic transitions. We examine the limits at which the conventional SR theories, which are based on the assumption of a plane-wave field in the vapor, start to fail. It is shown that at or above vapor densities of order ${10}^{17}$/${\mathrm{cm}}^3$, the frequency shifts of the SR line shape due to the local-field correction (Lorentz-Lorenz shift), the atom-wall interaction, and the nonexponential attenuation of the field in the vapor can have comparable orders of magnitude, and the proper determination of all these effects is essential for calculating the correct SR signals. A comparison of the theoretical SR spectra with an experimental result for a Rb vapor with a density of order ${10}^{17}$/${\mathrm{cm}}^3$ is also presented. © 1996 The American Physical Society.

We investigate the effect of a linear host medium on the dynamics of a dense collection of resonant atoms. We find that near dipole-dipole interaction is enhanced by the presence of the host dielectric, resulting in a lower threshold density and a greater hysteresis area for intrinsic optical bistability. Cooperative decay terms appear that represent the interaction of near dipoles mediated by the absorptive component of the dielectric function of the host medium. These terms are part of the local response and correspond to local cooperative decay effects. © 1996 The American Physical Society.

We present a general theory that connects the pump process in multilevel lasers with the statistics of the laser field. The key ingredient in our approach is the derivation of an effective master equation that involves only the two laser levels and that contains a non-Markovian pump term. This pump term gives rise to a narrowing of the photon-number distribution in steady state. The qualitative features of this dynamic noise reduction can be inferred from the eigenvalues of the pump term, which are known analytically. As the mechanism that is responsible for the noise reduction, we identify a correlated excitation process in which the effective excitation rate from the lower to the upper laser level depends on the photon number. This correlated excitation process is very different from an excitation at equidistant times, such as in lasers with periodic external injection. We stress that our approach is general and the treatment nonlinear because we do not resort to approximations such as an adiabatic elimination of atomic variables or the linearization of a Fokker-Planck equation. It is therefore particularly relevant for the description of systems where the active medium consists of a few atoms only and where the field losses are not negligible on the time scale of the atomic relaxations. This would be the case in an ion-trap laser. For such a situation our results are substantially different from those obtained by a linearized treatment. © 1996 The American Physical Society.

The electromagnetically induced transparency in a @sV-shaped atomic system is observed by a spectroscopy technique. The experimental results show that the absorption coefficient at maximum coherence is reduced by about 72% of the maximum absorption ${\mathrm{\alpha }}_0$, which is the case without the coherent effect. Meanwhile we also observed indirectly population trapping in the two excited states, which means that there is no decay via spontaneous or stimulated emission to the lower state. © 1996 The American Physical Society.

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. © 1996 The American Physical Society.

The "welcher Weg" (which-path) detector as described by Scully et al. [Nature 351, 111 (1991)] employs a pair of initially empty micromaser cavities placed in front of a double-slit apparatus in an atomic interferometer. Laser excited atoms spontaneously emit a photon into either cavity thereby marking the atoms' path and thereby destroying the interference. I propose an alternative method wherein at least one of the cavities is prepared in a coherent state with a strong amplitude. Which-path information is obtained by a nonresonant, dispersive type of atom-field interaction associated with quantum nondemolition measurements. Ground-state atoms passing through the cavity remain in the ground state but impart a phase shift to the cavity fields. Velocity selection is shown to affect the visibility of the fringes. An associated quantum eraser is also discussed.

We have measured the ${\mathit{D}}_1$ and ${\mathit{D}}_2$ Faraday spectrum and absorption spectrum of Rb atoms immersed in high-density Xe buffer gas in the range ${\mathit{n}}_{\mathrm{Xe}}$=0.8–4.5×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$. We find that the shape of the Faraday spectrum obeys the Becquerel relation over this whole density range; however the relative strength of the Faraday effect compared to absorption changes rather abruptly near ${\mathit{n}}_{\mathrm{Xe}}$=1×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$. This is ascribed to the onset of a many-body nature (overlapping collisions) of the Rb:Xe line broadening; the number of perturbers within the Weisskopf sphere is unity at ${\mathit{n}}_{\mathrm{Xe}}$∼1×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$. © 1996 The American Physical Society.

The dissociation of ${\mathrm{CO}}^{\mathit{Q}+}$ molecular ions (Q=4 to 9) produced in multiply ionizing collisions accompanied by the transfer of an electron to the projectile has been studied using time-of-flight techniques. Analysis of the coincident-ion-pair flight-time-difference distributions yielded average values of the kinetic-energy releases for the various dissociation reactions. These values were found to be as much as a factor of 2 greater than the kinetic-energy releases expected for dissociation along Coulombic potential curves. The average kinetic-energy release observed for a given ion pair with charges ${\mathit{q}}_1$ and ${\mathit{q}}_2$ are nearly equal to the point-charge Coulomb potential energies for an ion pair with charges ${\mathit{q}}_1$+1 and ${\mathit{q}}_2$+1, suggesting that the parent molecular ion is formed with two electrons, on average, in highly excited states that do not contribute to the screening of the nuclei. © 1996 The American Physical Society.

The quasicausal expansion of the quantum Liouville propagator is introduced into the Weyl-Wigner picture. The zeroth-order term is shown to lead to the statistical quasiclassical method of Lee and Scully [J. Chem. Phys. 73, 2238 (1980)]. © 1996 The American Physical Society.

We report observations of destructive quantum interference in multiphoton resonant excitation of high-lying Rydberg states in xenon. In a recent laser-induced breakdown experiment by Peet [Phys. Rev. A 51, 3982 (1995)], it was claimed that the interference was absent for such high-lying states. © 1996 The American Physical Society.

It is shown that the whole manifold of normally ordered field correlation functions can be obtained by averaging the measured quadrature component distributions with pattern functions, which are simply Hermite polynomials multiplied by an exponential phase factor. © 1996 The American Physical Society.