The intensities of high-order rotational Raman lines are calculated by computer simulation in the approximation of time-independent plane-wave pumping based on the currently accepted model used in studies of four-wave Raman mixing (FWRM). When the phases of the rotational lines are assumed to be slightly random, the intensities are drastically decreased. Such reduction in intensity becomes more serious with increasing phase distortion, indicating that the emission lines generated by FWRM requiring phase matching are coherently phased. In other words, phase matching is equivalent to phase locking or mode locking in FWRM. These results suggest that FWRM has potential for use in generating ultrashort optical pulses shorter than 1 fs.

The recently derived input-output relations for radiation at a dispersive and absorbing four-port device [T. Gruner and D.-G. Welsch, Phys. Rev. A 54, 1661 (1996)] are used to derive the unitary transformation that relates the output quantum state to the input quantum state, including radiation and matter and without placing frequency restrictions. It is shown that for each frequency component the transformation can be regarded as a U(4) group transformation, which can directly be calculated from the underlying complex refractive-index profile of the device without additional postulates. If for narrow-bandwidth radiation far from the medium resonances the absorption matrix of the four-port device can be disregarded, the well-known U(2) group transformation for a lossless device is recognized. Explicit formulas for the transformation of Fock states, coherent states, and phase-space functions are given.

We have measured spectrally resolved fluorescence lifetimes of dye incorporated in high-quality photonic crystals, made of colloidal spheres. The emission spectrum shows a pronounced Bragg notch. In contrast, the fluorescence lifetime does not depend on the interaction between light and the photonic crystal. The results are explained with a simple model of an atom in a cavity. The effects of homogeneous and inhomogeneous broadening of the emission spectrum of dye inside photonic crystals are discussed.

A large increase in atomic absorption due to coherent interaction with resonant radiation is predicted for a closed transition between two degenerate atomic levels verifying $0<\mathrm{}{F}_g<F_e{(F}_g$ and $F_e$ are the total angular momentum of the ground and the excited levels, respectively). In good agreement with the theoretical prediction, a total absorption enhancement by a factor 1.7 was obtained on the $D_2$ line of ${}^{85}\mathrm{Rb}\mathrm{}$ in a vapor cell experiment.

We discuss a simple one-dimensional (1D) model of the modification of Planck blackbody radiation by photonic band-gap materials (PBG’s). The model gives qualitative predictions for the thermal power spectrum of 2D and 3D PBG structures, and quantitative results for 1D, distributed Bragg reflecting PBG thin films.

The correlations arising between identical atoms resonantly coupled with the same radiation field are studied within a fully quantized theory. The atoms do not interact with each other and may be widely separated. We study how a modulation of the atom-field parameter of any one atom is transmitted to the others. This exchange of informations between remote systems was predicted in a previous account in the case of two atoms (signal transmission by optical correlations). In this paper, the theory is generalized to more than two atoms in order to model the effect of onlooker atoms. Outlines of experiments enabling investigation of the observability of these correlations and the applications that can be made are presented.

We present a theoretical model for the electrically pumped single-quantum-dot microsphere laser. We solve the master equation of the system and analyze the steady state and dynamical properties of the optical field, such as output power, photon number fluctuation, and linewidth, for realistic experimental parameters. The laser threshold power is several orders of magnitude lower than is currently possible with semiconductor microlasers. A semiclassical approximation for the output power and laser linewidth is derived and compared to the exact solution. Electrical pumping together with Coulomb blockade effect allows for the realization of regular pumping in the system. We discuss the possibility for the generation of heralded single photons and of sub-Poissonian laser light.

A study of the spatiotemporal evolution of a pulsed ${\mathrm{CO}}_2$ laser is performed using an experimental setup which allows transverse pattern recordings with 1-ns resolution. A rich laser dynamics, hidden until now behind temporal averages, is uncovered. Features like spontaneous symmetry breaking, mode beating, and phase locking are observed and theoretically interpreted using Maxwell-Bloch equations. Numerical simulations by means of mode decompositions are performed, showing very good agreement with the empirical results. The influence of the curvature of the mirrors in the dynamics of the system is also theoreticaly analyzed.

We have observed diffraction signals by a grating originating from electromagnetically induced transparency (EIT) in a three-level Λ system of cold sodium atoms. Theoretical and experimental analyses of this phenomenon, called the electromagnetically induced grating (EIG), have revealed that EIG spectra exhibit background-free, Lorentzian signal profiles regardless of the pump frequencies, making a clear contrast to the case of ordinary EIT spectra.

We have used a generic two-mode Hamiltonian with two associated time scales to study the evolution of generalized SU(1,1) coherent states, in particular the pair and Perelomov coherent states, which have been realized in many systems such as radiation fields, trapped ions, and phonons. We have found that their dynamics does not depend on the ratio of these time scales but is instead determined crucially by the difference in photon numbers of the two modes. This is in stark contrast to the previously studied harmonic-oscillator coherent states and can be attributed to the different nature of the underlying algebra. We provide analytical results for their revival and fractional revival along with numerical plots of the autocorrelation function and the quadrature distribution and demonstrate the formation of Schrödinger cats. The results are extremely sensitive to the Casimir invariant and the complex parameters characterizing SU(1,1) coherent states.

We report observations of conical emission from a pulsed laser beam with incident laser power, detuning, and beam diameter matched to a range of single, steady-state filaments. The beam thus propagates with nearly constant diameter through 5 cm of strontium (Sr) vapor. Emission angles $\left(\theta \right)$ are imaged as the height on the input slit of a 1.5 m spectrometer; a charge-coupled device camera in the spectrometer exit plane measures energy as a function of $\theta$ and frequency. Data are reported versus laser-pulse energy, diameter and detuning, and the collisional dephasing rate. Spectrally broad, red-detuned cones are observed, but only when the laser beam is predominately self-trapped. As previously observed in experiments where the beam breaks up into multiple filaments, forward emission at the blue-detuned Rabi sideband is much weaker than at the red (cone) sideband. The cone angle is largely independent of the phase velocity of the self-trapped laser beam, which varies from the vapor to the vacuum speed. The efficiency of the cone emission shows incomplete saturation, as well as strong dependence on self-trapped filament parameters.

I present an iterative algorithm for reconstructing the Wigner function from homodyne statistics. The proposed method, based on maximum-likelihood estimation, is capable of compensating for detection losses in a numerically stable way.

The Greenberger-Horne-Zeilinger (GHZ) paradox is subject to the detector-efficiency “loophole” in a similar manner as the Bell inequality. In a paper by J.-Å. Larsson [Phys. Rev. A 57, R3145 (1998)], the issue is investigated for very general assumptions. Here, the assumptions of constant efficiency and independent errors will be imposed, and it will be shown that the necessary and sufficient efficiency bound is not lowered, but remains at $75\%$. An explicit local-variable model is constructed in this paper to show the necessity of this bound. In other words, it is not possible to use the independence of experimental nondetection errors to rule out local realism in the GHZ paradox below $75\%$ efficiency.

Spherically averaged electron momentum densities $\Pi \mathrm{}\left(p\right)\mathrm{}$ are constructed by the numerical Hartree-Fock method for 54 singly charged atomic cations from ${\mathrm{He}}^{+}$ (atomic number $Z=2)$ to ${\mathrm{Cs}}^{+}$ $\mathrm{}(Z=55\mathrm{})\mathrm{}$ and 43 anions from ${\mathrm{H}}^{\mathrm{-}}$ $\mathrm{}(Z=1\mathrm{})\mathrm{}$ to ${\mathrm{I}}^{\mathrm{-}}$ $\mathrm{}(Z=53\mathrm{})\mathrm{}$ in their experimental ground state. As in the case of neutral atoms, the Hartree-Fock momentum densities for all these ions can be classified into three types; 28 cations and 10 anions have a unimodal density with a maximum at $p=0,$ 22 cations and 21 anions have a unimodal density with a maximum at $p>\mathrm{}0,$ and 4 cations and 12 anions have a bimodal density with a primary maximum at $p=0\mathrm{}$ and a secondary maximum at $p>\mathrm{}0.\mathrm{}$

The possibility of electron attachment to the valence $a{}^3\Pi$ state of CO is examined using an ab initio bound-state multireference configuration interaction approach. The resulting resonance has ${}^4{\Sigma }^{-}$ symmetry; the higher vibrational levels of this resonance state coincide with, or are nearly coincident with, levels of the parent $a{}^3\Pi$ state. Collisional relaxation to the lowest vibrational levels in hot plasma situations might yield the possibility of a long-lived ${\mathrm{CO}}^{-}$ state.

The modified Faddeev equations are used to calculate the complete multichannel K matrices within the energy gap between the $\mathrm{Ps}\mathrm{}(n=1\mathrm{})\mathrm{}$ and $\mathrm{Ps}\mathrm{}(n=2\mathrm{})\mathrm{}$ thresholds. We report here a number of partial cross sections in this energy range including hydrogen production cross sections in the Ps entrance channel. The angular momentum states calculated are S, P, D, and F states. The number of open channels ranges from two in the Ore gap to four and five above the $\mathrm{H}\mathrm{}(n=2\mathrm{})\mathrm{}$ threshold. Comparison with previous calculations is made whenever feasible. Agreement within a few percentages is observed for most cases.

The Coulomb explosion of ${\mathrm{CO}}_2$ in collisions with ${\mathrm{Ar}}^{8+}$ ions of 120 keV has been examined experimentally using a position sensitive detector with a triple coincidence technique. The technique has allowed the full characterization of the structure of the exploding molecule. Purely Coulombic fragment energies fit the experimental results well, across the range of fragment energies. Modifications to the molecular geometry are observed, in the form of widening of the zero point bend distribution and sequential processes are found to be unimportant in the dissociation process.

Experimental absolute-rate coefficients for electron-impact excitation of ${\mathrm{C}}^{3+}\hspace{0.5em}(2s{}^2{S}_{1/2}\to 2p{}^2{P}_{1/2,3/2})$ near threshold [D. W. Savin, L. D. Gardner, D. B. Reisenfeld, A. R. Young, and J. L. Kohl, Phys. Rev. A 51, 2162 (1995)] have been reanalyzed to include a more accurate determination of optical efficiency and revised radiometric uncertainties which reduce the total systematic uncertainty of the results. Also, new R matrix with pseudostates (RMPS) calculations for this transition near threshold are presented. Comparison of the RMPS results to those of simpler close-coupling calculations indicates the importance of accounting for target continuum effects. The reanalyzed results of Savin et al. are in excellent agreement with the RMPS calculations; comparisons are also made to other measurements of this excitation. Agreement with the RMPS results is better for fluorescence technique measurements than for electron-energy-loss measurements.

A method is proposed for calculating the ratio of triple to double ionization and a number of calculations of the ratios of double to single and triple to double ionization are given for neutral and singly ionized lithium.

Very-low-energy scattering of orthopositronium by helium has been investigated for the simultaneous study of elastic cross section and pickoff quenching rate using a model exchange potential. The present calculational scheme, while it agrees with the measured cross section of Skalsey et al., reproduces successfully the parameter ${}^1{Z}_{\mathrm{eff}},$ the effective number of electrons per atom in a singlet state relative to the positron. Together with the fact that this model potential also leads to an agreement with measured medium energy cross sections of this system, this study seems to resolve the long-standing discrepancy at low energies among different theoretical calculations and experimental measurements.