Through a study of the spontaneous rotation of laser patterns, a phenomenon that appears in class-A lasers with a cylindrically symmetric configuration and a homogeneous active medium, we found that class-A lasers support the spontaneous creation of three types of rotational patterns. We derived analytically a general cooperative relation to describe the spontaneous rotation of these patterns. This relation contains three characteristic frequencies: the central carrier frequency, the rotational frequency of the pattern, and the frequency spacing between the transverse cavity modes.

We apply the concept of the mazer to the two-photon process and propose the idea of the two-photon mazer. We establish the general quantum theory of the two-photon mazer and calculate its emission probability in the special case of a mesa mode function. We study not only the case in which the cavity field is initially in a number state, but also the case in which the cavity field is initially in a coherent state. Under the condition of an initial coherent field, the emission probability shows the collapse-revival phenomena, which have different features in different regimes. In the thermal-atom regime, the collapse revivals are similar to that in the two-photon Jaynes-Cummings model. In the critical regime, the collapse revivals look like that in the one-photon Jaynes-Cummings model. In the ultracold-atom regime, the collapse revivals are different from those in the above two regimes. The reasons for these results have been analyzed.

The propagation of resonant $0\pi$ pulses in atomic rubidium is investigated experimentally and theoretically. In order to explain the observed pulse shaping, the hyperfine structure of the $D1\mathrm{}$ transition for both isotopes is included. The influence of the hyperfine structure is also demonstrated by comparison between measurements in a natural mixture of atomic rubidium and pure rubidium 87. The characteristic difference between pulse shapes for moderate and large absorption is explained by means of a transfer function.

We developed a model for the intensity noise of a multimode semiconductor laser which includes both the nonlinear gain and the nonlinear loss. The nonlinear gain stems from spectral hole burning and population pulsation. Saturable absorption by deep trap levels results in the nonlinear loss. We find that the nonlinear gain alone does not enhance the total intensity noise above the quantum efficiency limit. The nonlinear loss, however, does increase the intensity noise when longitudinal side modes have considerable intensities, and thus explains the observed excess intensity noise. In this case the perfect anticorrelation among the longitudinal modes is degraded, which in turn converts the mode-partition noise to the total intensity noise. We remark that larger (smaller) saturable absorption in the quantum-well (transverse-junction-stripe) lasers could explain the larger (smaller) excess noise behavior observed in these lasers.

We propose to test experimentally the nonclassical character of radiation states through homodyne tomography. For single-mode states we check violations of inequalities involving the photon-number probability. For two-mode states we test the nonclassicality by reconstructing some suitable number-operator functions. The test can be performed with available quantum efficiency of homodyne detection, by measuring the pertaining quantities on the corresponding noisy states.

The dynamics of a quasi-isotropic continuous-wave solid-state laser sustaining the oscillation of two orthogonally polarized eigenstates is experimentally investigated. A set of phase-sensitive vectorial Maxwell-Bloch equations is developed to describe theoretically the evolution of such a laser. Different temporal behaviors for the output intensities are observed, depending on the relative amounts and orientations of the phase and loss anisotropies and on the frequency of relaxation oscillations. Namely, the frequency locking of the two orthogonally linearly polarized eigenstates is shown to lead to a surprising pulsed mode-locked oscillation regime. In addition, for different values of the parameters, other peculiar operation regimes are found, such as cw circularly polarized, double-pulsed, or triple-pulsed output intensities. These experimental results, obtained using a diode-pumped Nd:YAG (YAG denotes yttrium aluminum garnet) laser, are well confirmed by the theoretical model.

The quadrature squeezing spectra produced in the resonance fluorescence of a two-level atom are investigated, including the effects of a finite laser bandwidth due to phase diffusion. For resonant excitation at low intensities, the fluorescence field exhibits narrow bandwidth squeezing in the out-of-phase quadrature, centered at the laser frequency. Otherwise, squeezing occurs only in the in-phase quadrature. Specifically, for slightly off-resonance and weak excitation, the squeezing still centers at the laser frequency, with a finite bandwidth of the order of $\gamma .$ More importantly, for far-off-resonance and strong excitation, the resonance fluorescence exhibits two-mode squeezing around the Rabi sideband frequencies. Thus we have a source of two-mode squeezing that is very easily frequency tuned simply by adjusting the generalized Rabi frequency. The presence of a laser linewidth substantially reduces the degree of squeezing obtainable. The fluorescence shows no squeezing at all when the laser linewidth is greater than the atomic spontaneous emission linewidth.

Amplification without inversion in the presence of collisions in V and Λ systems is studied within the framework of density-matrix formalism. We show that while it is possible to achieve amplification without inversion close to Raman resonance in both systems, it is affected by collisions in a different way. In the V system, collisions enhance quantum interference, whereas in the Λ system they quench it. This effect depends crucially on the collision characteristics, essentially on the relative values of the collisional relaxation rates for the Raman coherence and for the optical coherences. For the Λ system, different incoherent pumping processes are studied: pumping via the upper level and direct pumping between the two low-energy levels. The direct pumping process is interesting for the frequency up-conversion of the coherent and incoherent pump fields. Furthermore, with direct pumping the gain always occurs without inversion.

It is shown that the interaction of ultrashort laser pulses with nonstationary semiconductor plasmas can, under appropriate conditions, lead to a variety of interesting phenomena including controlled upshifting of the laser frequency, leading to the possibility of tunable lasers in a wide range of frequencies, and trapping (nonpropagation) of a substantial part of the incident pulse.

We investigate the spontaneous emission rate of ${\mathrm{Eu}}^{3+}$ ions in an asymmetric microcavity. The cavity consists of a thin dielectric layer bounded on one side by silver and on the other by air. Samples were constructed using the Langmuir-Blodgett technique, the emitters being incorporated as a single monolayer within the microcavity. This technique allowed both the cavity thickness and the position of the emitters within it to be controlled to one monolayer (≈2.6 nm). Measurements are presented of the spontaneous emission decay rate as a function of both the dielectric layer thickness and the position of the emitters within the layer. We find good agreement between our data and a classical model. The model allows us to investigate the role of the electromagnetic modes of the microcavity in controlling the spontaneous emission decay rate of the emitters. In particular, we are able to evaluate the contribution each of the modes makes to the decay. We discuss the implication these results may have in increasing the photoluminescence efficiency from microcavity based emissive devices.

The first ionization potentials ($V_{\mathrm{IP}}$’s) of copper, silver, and gold have been reassessed using a two-color resonant excitation scheme on laser-vaporized atomic beams of Cu, Ag, and Au. Rydberg levels of the ${\mathrm{nd}}^{10}{n}_R{s}^1{(}^2{S}_{1/2})$ and ${\mathrm{nd}}^{10}{n}_R{d}^1{(}^2{D}_{3/2,5/2})$ series converging to the ground ${}^{1}S$ term of the singly charged cations were excited and pulse-field ionized. The fit to the Rydberg levels yielded the ionization potentials $V_{\mathrm{IP}}\mathrm{}\left(\mathrm{Cu}\right)\mathrm{}=62\mathrm{}317.3\left(2\right)\mathrm{}{\mathrm{cm}}^{\mathrm{-}1},$ $V_{\mathrm{IP}}\mathrm{}\left(\mathrm{Ag}\right)\mathrm{}=61\mathrm{}106.45\left(20\right)\mathrm{}{\mathrm{cm}}^{\mathrm{-}1},$ and $V_{\mathrm{IP}}\mathrm{}\left(\mathrm{Au}\right)\mathrm{}=74\mathrm{}409.0\left(2\right)\mathrm{}{\mathrm{cm}}^{\mathrm{-}1}.$ A comparison of these results to the currently accepted values revealed slight discrepancies to the previously reported IP of silver.

The differential equation of the mean electric-dipole moment induced by a laser field in a two-level atom is that of a driven parametric oscillator with time-dependent frequency. In the case of a laser field with constant intensity, a connection with the Mathieu equation is stated and it is shown from the known theory that the spectrum emitted must present only odd harmonics of the pumping field.

We report differential elastic cross sections for low-energy electron scattering by ${\mathrm{CHF}}_3$, ${\mathrm{CH}}_2{\mathrm{F}}_2$, ${\mathrm{CH}}_3$F, ${\mathrm{CHCl}}_3$, ${\mathrm{CH}}_2{\mathrm{Cl}}_2$, ${\mathrm{CH}}_3$Cl, ${\mathrm{CHCl}}_3$, ${\mathrm{CF}}_2{\mathrm{Cl}}_2$, and ${\mathrm{CF}}_3$Cl, obtained with the Schwinger multichannel method with norm-conserving pseudopotentials. Our results are in excellent agreement with available experimental and theoretical data. We compare the present results with our previous results for ${\mathrm{CH}}_4$, ${\mathrm{CF}}_4$, and ${\mathrm{CCl}}_4$ and show that the oscillatory behavior of the cross sections is related to electron scattering from heavier centers (F or Cl), which favors the coupling of high partial waves. We also include a table with momentum-transfer cross sections.

We have performed continuous slowing of an atomic beam to load a magneto-optical trap (MOT) on axis. To avoid the undesirable effects of the strong slowing laser on the performance of the MOT, a dark spot in the center of the slowing laser beam is used. We varied the spot size and the slowing-laser frequency and intensity to optimize the number of trapped atoms. Our “dark-spot” slowing increased the number of trapped atoms by a factor of 30, allowing us to trap $\sim {10}^9$ atoms in the MOT.

We report on the efficient operation of a double-magneto-optical-trap (MOT) apparatus for potassium isotopes. Mechanisms for the cooling and the transfer between the two MOTs are studied. A magnetic quadrupole trap has been loaded from the second MOT; density and temperature appear to be promising for starting runaway evaporative cooling.

We have observed violet photon emission resulting from energy-pooling collisions between ultracold Rb atoms illuminated by two colors of near-resonant infrared laser light. We have used this emission as a probe of doubly excited state ultracold collision dynamics. By varying the detuning of the lasers, we have clearly identified the effect of spontaneous emission on the collision process.

Because of the orbital degeneracy, the optical pulse induced redistribution of the initial single-state population over different-l Rydberg states in the hydrogen atom cannot be probed by, e.g., the traditional ramped-field ionization or the combination of this technique with the two-pulse Ramsey interferometry. The model calculations performed by us for the ionization from a low-lying hydrogenic state via high Rydberg states suggest that such a probe for the different-l spreading could be the photoelectron angular distributions measured versus laser intensity.

Contrary to claims contained in papers by Grot, Rovelli, and Tate [Phys. Rev. A 54, 4676 1996)] and Delgado and Muga [Phys. Rev. A 56, 3425 (1997)], the “time operator,” which I have constructed [Rep. Math. Phys. 6, 361 (1974)] in an axiomatic way, is a self-adjoint operator existing in a usual Hilbert space of (nonrelativistic or relativistic) quantum mechanics.

Majumdar and Sharatchandra recently proposed a set of “coherent states” for the hydrogen atom [Phys. Rev. A 56, R3322 (1997)]. These states satisfy some of the typical properties of coherent states, such as, for example, continuity in the parameters. The time evolution of these states is given by the classical evolution of the angle variables, and the expectation values of the quantum observables behave quasiclassically. However, those authors also claimed that, although one does not obtain exactly the same state after a Kepler period, the gross features of their wave packets do not change. We show that this is not correct, and that these wave packets do not remain localized on the classical variables, but spread rapidly over the Keplerian orbit. The localization properties of these states do not improve in the limit of large quantum numbers.

Quang and John have, in a recent paper [Phys. Rev. A $56,$ 4273 (1997)], proposed a dressed-state Monte Carlo wave-function (MCWF) approach to a laser-driven two-level atom coupled to a structured radiation reservoir. In this Comment, we argue that this approach is at variance with the underlying physical idea of the MCWF technique, that it is at variance with basic formal requirements for the MCWF technique to apply, and that it produces spurious and unphysical quantitative results for wide ranges of parameters.