In this paper we present some of the general features of autoionizing Rydberg wave packets. We assume the wave packets are generated by a short, perturbative laser pulse that excites the electronic wave function to a coherent distribution of final state energies in the autoionizing regime. We describe a possible experiment for generating and detecting these autoionizing wave packets. A physical effect we call ‘‘cresting of a wave packet’’ is described. Several calculations for Ba are presented. The cresting of the ejected wave packets should be observable for this atom. Several other effects may also be of interest: the suppression of particular wave packets, the angular distribution associated with a wave packet, different decay rates in different directions, and the systematic variation of angular distribution with the delay time. © 1996 The American Physical Society.

A one-dimensional model of ${\mathrm{H}}_2$ is used to examine the nonlinear behavior of a pair of electrons in the presence of intense laser fields and fixed nuclei. We present ionization rates of ${\mathrm{H}}_2$ at different frequencies and intensities of short intense electromagnetic pulses by solving exactly the time-dependent Schrödinger equation for the above system as a function of internuclear distance. Anomalously high ionization rates are found at large critical internuclear separations, akin to similar results found previously in the one-electron molecule ${\mathit{H}}_2$${\mathrm{}}^{+}$. Independent one-electron and simultaneous two-electron ionizations are identified from the numerical simulations to occur at different intensities and frequencies. Field-induced barrier suppression models are shown to explain qualitatively the numerical results. © 1996 The American Physical Society.

Velocity (mode) selection accumulates atoms in long-lived atomic (dark) states thereby reducing the entropy and energy. We present a scheme using a two-frequency laser field acting on two separate dipole transitions that supports dark atomic states in a spatially arbitrary three-dimensional (3D) field configuration. Monte Carlo simulations of a 1D model of velocity selection demonstrate a reduction of the velocity spread of the atomic ensemble to less than 1 nK. Schemes to combine selection and trapping of atoms to reduce phase space density in 3D by mode selection are discussed. © 1996 The American Physical Society.

We have measured separately the ionization threshold fields of the sets of Li states composed of l+m even and l+m odd zero field states. In spite of the fact that the states composed of l+m even states are, by one measure, more nonhydrogenic than those composed of the l+m odd states, we observe that both sets of states ionize at a microwave field well below the hydrogenic ionization field. The ionization of the states composed of l+m odd states shows that even small departures from hydrogen lead to completely nonhydrogenic ionization, as in a static field. In contrast, in a linearly polarized microwave field small departures from hydrogen do not lead to nonhydrogenic ionization. The excitation spectrum of the states composed of l+m odd states exhibits regular structure, while that of the states composed of l+m even states does not, a difference due to the differing energy shifts of m=0 and ±1 states on transformation between the laboratory and rotating frames. © 1996 The American Physical Society.

We show that the problem of the net absorption of one photon from a strong laser pulse in a bound-to-continuum transition can be recast as a single integral equation. For a certain class of absorption spectra, this integral equation can be converted to a second-order Schrödinger-like differential equation, which can be accurately solved in an essentially closed form using the semiclassical uniform approximation. With the aid of the integral equation and the uniform solutions we find that for strong short pulses, irreversible transitions to a perfectly absorbing continuum in the weak-field regime become reversible. In particular, continuum levels may execute Rabi oscillations with the precursor bound state. These oscillations occur at different frequencies, depending on the continuum energy. As a result, spectral migrations and formations of transparent lines may occur. Field-induced interferences between neighboring lines is also investigated. © 1996 The American Physical Society.

We develop a method for reconstructing the quantum mechanical state of a trapped ion by bichromatically irradiating it on a weak electronic transition and subsequently probing a strong electronic transition for resonance fluorescence. Based on this recently proposed scheme [S. Wallentowitz and W. Vogel, Phys. Rev. Lett. 75, 2932 (1995)] the density matrix of the vibrational motion can be readily obtained either in a generalized position representation or in the number-state representation. The method allows to uniquely define an ultimate classical noise level by a reference measurement with an ion cooled to its vibrational ground-state. Disturbations of the measurement and their suppression are considered. Moreover, we study the effect of the back action of the measurement principle on the motional quantum state. It consists in the splitting of the state to be measured into two substates, giving rise to quantum interference effects. © 1996 The American Physical Society.

Analysis of the relative angular response of the degenerate four-wave mixing signal in alkali-metal atoms mixed with a buffer gas allows direct determination of the excited-state diffusion coefficients. The measured diffusion coefficients D at 96 °C and 760 torr for the cesium 6${\mathit{P}}_{1/2}$ and 6${\mathit{P}}_{3/2}$ state atoms in neon gas are 0.348(4) ${\mathrm{cm}}^2$ ${\mathrm{s}}^{\mathrm{-}1}$ and 0.281(8) ${\mathrm{cm}}^2$ ${\mathrm{s}}^{\mathrm{-}1}$, respectively. © 1996 The American Physical Society.

The nature of a class of states of a given mode of a high-Q cavity, which can be produced by suitable postselection experiments, is investigated in terms of phase-space representations of the associated density operators. It is shown that these states have hollow Wigner functions and can be well approximated by coherent superpositions of pairs of squeezed states in many different ways. A remarkable property of these states is that the coherence properties associated with the volcano shape of their Wigner distributions last a fairly long time when usual damping contributions are considered. A procedure to generate these states and to analyze their sub-Poissonian components is proposed. © 1996 The American Physical Society.

Space-dependent Maxwell-Bloch equations are derived for the description of spatiotemporal dynamics of spatially inhomogeneous semiconductor lasers. The dynamics of the charge carriers is described in a density-matrix approach using a Wigner function representation. On this basis, the coupled set of equations of motion for the active medium and the space-dependent light field is derived. Based on typical length and time scales, approximations are performed to obtain a numerically tractable problem. The many-body interactions give rise to space-dependent energy renormalizations, Coulomb enhancement, and scattering processes. The latter ones are considered in the form of momentum- and density-dependent microscopic relaxation rates due to carrier-carrier and carrier-phonon interaction for the carrier distribution functions and the polarization. For the spatial transport or the carriers an ambipolar diffusion model is derived. © 1996 The American Physical Society.

The spatiotemporal dynamics of broad-area lasers is analyzed on the basis of a space- and momentum-dependent density-matrix approach. To this means the space-dependent Maxwell-Bloch equations for the semiconductor laser (derived in our preceding paper I) are solved by direct numerical integration. The space and momentum resolved dynamics of the active semiconductor medium, described by microscopic charge-carrier distributions and nonlinear polarization functions, are treated self-consistently with the spatiotemporal dynamics of the light field. Carrier transport dynamics are approximated on the basis of an ambipolar diffusion approximation consistent with the microscopic processes. Boundary-influenced macroscopic waveguiding properties of typical conventional as well as tapered broad-area laser cavities are taken into account. The dynamics of the formation and longitudinal propagation of unstable transverse optical filamentary structures are analyzed. Simultaneous spectral and spatial hole burning with dynamical spatiospectral variations on ultrashort (ps and sub-ps) time scales are observed in the charge-carrier distributions, reflecting the interplay between stimulated emission and the relaxation dynamics of the carrier distributions as well as the polarization. The transverse hole burning leads to complex spatiotemporal patterns in the macroscopic intensity picture with different optical frequencies associated with various locations of the modelike near-field patterns. © 1996 The American Physical Society.

We discuss a model involving the interaction of a single-mode field with both a Kerr medium and a parametric nonlinearity of the kth order. The system is externally driven by the parametric pump field. We show that applying an appropriately chosen field frequency, and for weak nonlinear process, k-photon Fock state of the electromagnetic field can be achieved. © 1996 The American Physical Society.

The master-equation theory for multimode semiconductor lasers [A. Eschmann and C. W. Gardiner, Phys. Rev. A 54, 760 (1996)] is adapted to treat the case of an injection-locked laser. Both the intensity noise and the phase noise of the system are examined. A decrease in the total intensity noise and in the inten- sity noises of the individual modes is found for increasing injection power, provided the injection signal does not dominate the entire system. A regime is found in which a reduction of the intensity noise below the shot noise level is obtained which is not single-mode squeezing, but which is due to anticorrelations between the individual modes, and a further regime in which true single-mode squeezing exists is also found. The phase noise is found to decrease with increasing injection strength, in other words as phase locking occurs. © 1996 The American Physical Society.

Using the random telegraph model, we investigate optical dephasing processes arising from Poisson stochastic modulation, we obtain the analytic expression for free-induced decay (FID) and photon-echo decay in the whole range of the stochastic parameters. In the small modulation range, FID or echo-intensity decay varies from single exponential to multiexponential with the increase of frequency modulation. In the large modulation range, FID is a damping oscillation, and the echo intensity decays exponentially with periodical fluctuations. When the modulation is very large the echo-intensity decay tends to go back to an exponential. The ${\mathit{R}}_1$(-3/2) echo-intensity decay in ruby at high magnetic fields is calculated based on the analytic expression; the result is compared with experiments and computer simulations. © 1996 The American Physical Society.

The conditions of observation of direct two-photon-induced dispersion in three-level reflection spectroscopy at a vapor-dielectric interface are discussed. One shows how pump frequency modulation allows one to discriminate the two-photon singular contribution associated with atoms moving quasiparallel to the dielectric interface, and therefore single out off-resonant Doppler-free two-photon dispersion in selective reflection. A nonperturbative theoretical approach to two-photon reflection is shown to predict a dynamic Stark shift of the two-photon resonance, which has been experimentally observed on the 6S-6P-8S transition of cesium. © 1996 The American Physical Society.

The propagation of a pair of electromagnetic pulses through a coherently prepared atomic medium in the Λ configuration is studied. We find that even in an absorbing medium, it is possible to produce pulses that propagate shape invariant. The results reveal the spatiotemporal dynamics associated with field propagation, and highlight the role of atom preparation, pulse intensities, and medium length, on the final output pulses that one obtains. We also explore the prospects for pulse shaping and control by using dissimilar shaped pulses at the input to the medium and following their evolution. © 1996 The American Physical Society.

We present and test against experiment a general technique that allows modular modeling of noise propagation in quantum optics experiments. Specifically, we consider a multielement frequency-doubling experiment that ultimately produces 1.7 dB/32% (3.0 dB/50% inferred) squeezing at 532 nm. Unlike previous theoretical treatments, we obtain completely analytical expressions for each element of the experiment. This allows intuitive analysis and straightforward experimental modeling. The exact role of driving noise is demonstrated: addition of a narrow linewidth mode cleaning cavity to reduce the driving noise improves the inferred squeezing from 0.75 to 3.0 dB. We find excellent agreement between the modular theory and experiment. © 1996 The American Physical Society.

The dynamics of a ${\mathrm{CO}}_2$ laser with ${\mathrm{SF}}_6$ gas in an intracavity cell was studied by detection of the output pulse intensity average as a function of the laser cavity tuning. The derivative of this average power with respect to the control parameter shows the bifurcations, associated with periodic and chaotic regimes, previously identified in these lasers. The technique can be relevant to study the dynamics in high pulse rate lasers and other nonlinear systems where the average of a specific variable has a significant effect. © 1996 The American Physical Society.

We study the response of a two-mode laser to an external periodic pump modulation of small amplitude. The control parameters are the pump-modulation frequency and amplitude. We first show that the ratio of the two relaxation oscillation frequencies may be commensurate. We then investigate the parameter domain in which the lowest of the two relaxation oscillation frequencies is close to half the other relaxation oscillation frequency. We derive analytically a pair of nonlinear amplitude equations for the dynamical modes of the system. This gives access to the stability of the time-periodic solutions that oscillate at the pump-modulation frequency and its first (sub)harmonic. It also determines the occurrence of secondary bifurcations leading to more complex solutions. © 1996 The American Physical Society.

We consider a single perfectly reflecting plane mirror moving in the vacuum of the electromagnetic field, in the nonrelativistic approximation. We calculate the frequency and angular spectra of the emitted radiation. Photons are created in pairs, implying some simple and general properties of the spectra. In the case of TM-polarized photons, the angular distribution is concentrated on a particular direction that depends on the photon frequency, whereas TE photons are smoothly distributed around the direction perpendicular to the surface of the mirror. The total radiated energy is shown to be related to the dissipative force exerted on the mirror, in agreement with energy conservation. © 1996 The American Physical Society.

Biconical emission with wave-number ratio √2 is observed in the numerical simulations of the ring cavity with diffraction effects, on the defocusing side of the resonance. As the intensity of the plane-wave input beam increases, a sequence of stationary patterns is observed, and understood via a nonlinear analysis. The first pattern with (4-4) peaks is a bisquare resulting from a strong coupling between two quasiresonant sets of modes with wave numbers K and √2K. This pattern destabilizes at the onset of the drift bifurcation, into a new (4-4) pattern with a smaller wavelength, that splits into two twisted bisquares, with a 53° rotation angle ensuring the wave-vector locking, or the spatial periodicity of this (8-8) structure. © 1996 The American Physical Society.