The influence of intratarget relativistic effects on electron spin polarization is studied for low-energy electron scattering from Ca, Sr, Ba, and Yb atoms, for which a low-lying d-wave shape resonance is predicted. The motion of the scattering electron is described by solving the continuous-state Dirac-Fock equations plus a parameter-free correlation-polarization potential. The targets are represented using Dirac-Fock, Cowan’s quasirelativistic Hartree-Fock, and nonrelativistic Hartree-Fock wave functions, in which the intra-atomic (also called the indirect) relativistic effects are incorporated in varying degrees. It is shown that the intra-atomic relativistic effects, in particular the spin dependence of the Dirac-Fock one-electron orbitals, create apparent quantitative changes in the spin polarization parameters around the d-wave shape resonances.

The valence shell photoionization branching ratios of atomic oxygen are measured at the multiplet term level in a synchrotron-radiation-based electron spectrometry experiment and calculated using the multiconfiguration Hartree-Fock (MCHF) method for photon energies between 20 and 212 eV. The [2p]${(}^4$S${,}^2$D${,}^2$P) branching ratios, [2s${]}^2$P to [2s${]}^4$P intensity ratio, and [2s] to [2p] cross-section ratio for removal of a 2s or 2p electron are presented, and satisfactory agreement between the experiment and the MCHF calculation is found. In addition, the relative photoionization cross section is measured between 24 and 122 eV and is compared with calculations and a previous absolute cross-section measurement. Good agreement between the experimental and MCHF results is seen.

Electron energy-loss spectra (EELS) of ${\mathrm{SF}}_6$ have been recorded in the region of S 2p, S 2s, and F 1s excitation, using both dipole and nondipole electron-scattering conditions. Impact energies between 700 and 3200 eV and scattering angles between 0° and 30° were used. Relative to dipole EELS or photoabsorption, there are large intensity redistributions in both the S 2p and S 2s spectra under nondipole conditions. In contrast, the F 1s spectrum is essentially the same in near-dipole and nondipole scattering regimes. A higher-order electric multiple S 2p spectra feature is observed at 181 eV. It has an unusual multipeaked line shape whose components are more closely spaced than the typical 1.15-eV S 2p spin-orbit splitting. It is attributed to the overlap of several quadrupole-coupled states, which are likely associated with the [S 2p(${\mathit{t}}_{1\mathit{u}}$${)}^{\mathrm{-}1}$,${\mathit{t}}_{1\mathit{u}}$] configuration. Ab initio self-consistent field calculations for various open-shell S 2p excited states are used to assist spectral assignments.

The generalized oscillator strengths (GOSs) for discrete and continuum S 2p excitations of ${\mathrm{SF}}_6$ have been derived in the momentum transfer range (${\mathit{K}}^2$) of 1–20 a.u${.}^{\mathrm{-}2}$ from the angular variation of the relative differential cross section for inelastic electron scattering. The experimental techniques and data processing procedures used to obtain reliable, absolute GOS values are documented. The GOS results are compared to recent literature results [J. F. Ying, C. P. Mathers, and K. T. Leung, Phys. Rev. A 47, R5 (1993)]. Some discrepancies are noted. These are found to arise largely, but not completely, from differences in the data analysis procedures used. The Bethe surface for ${\mathrm{SF}}_6$ in the region of S 2p excitation is derived and the important role of Compton scattering by valence electrons is illustrated.

The emission of K x-rays following the irradiation of solid Ne at various pressures is investigated. A cryogenic target of solid Ne at vapor pressure is obtained by the condensation of Ne gas on an aluminum backing maintained at a temperature of 5.5 K. This target is irradiated with 2-MeV ${\mathrm{H}}^{+}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$, and the evolution of the target is controlled by the detection of backscattered particles. X-ray emission following the ionization of Ne is also detected during irradiation. It is observed that the x-ray spectra do not significantly differ from the atomic spectrum recorded on Ne gas. Samples of metals implanted with Ne ions are irradiated with 4-keV electrons and K x-ray spectra from Ne are recorded. Important broadening effects are observed on the K${\mathrm{\alpha }}_{1,2}$ lines; the satellites from double ionization are less seriously affected. It is observed that the total width of the K${\mathrm{\alpha }}_{1,2}$ band is directly related to the shear modulus of the metal.

We employ a vector quantum field theory to describe the interaction of a coherent atomic beam with a standing-wave laser field. The coherent atomic beam is assumed to be composed of degenerate bosonic atoms. We derive a nonlinear Schrödinger equation to describe the diffraction of the coherent atomic beam through the standing-wave laser field in the adiabatic regime of interaction of atoms with a light wave. Under appropriate conditions, we find that the standing-wave laser field acts as a quantum nonlinear atomic beam splitter for a coherent atomic beam. The quantum correlations in the nonlinear atomic beam splitter are analyzed and the analogy to quantum correlations of nonclassical light in an optical Kerr-type medium is discussed.

A cloud of atoms reflecting from an evanescent-wave mirror produces a phase shift on the beam producing the evanescent wave. This shift can be used to detect the passage of the atoms. We give a physical discussion of this process and estimate the phase shift. The shift can be greatly increased by using a resonant planar waveguide. We also estimate the signal-to-noise ratio and show how to optimize the experimental parameters of such a measurement. Using the waveguide we find a signal-to-noise ratio of order of 300 in a realistic experimental situation.

Laser cooling in a trap is investigated for laser and trapping configurations which allow the existence of approximate ‘‘dark states’’ of the combined atom-plus-trap system, i.e., states that are decoupled from the laser light by quantum interference. We show that a one-dimensional (1D) free-particle dark state in angular momentum ${\mathit{J}}_{\mathit{g}}$=1 to ${\mathit{J}}_{\mathit{e}}$=1 transitions and in two counterpropagating laser fields survives as an approximate dark state in a ‘‘flat-bottom’’ trap of size much larger than the optical wavelength. Furthermore, we show the existence of approximate dark states in 1D harmonic-oscillator potentials. In the latter configuration we are able to provide analytical results.

We have used amplified, programmable, shaped optical pulses to engineer Rydberg wave packets in cesium. Our apparatus employs a computer-controlled liquid-crystal pulse shaper which could control either the phase or the magnitude of the pulse’s spectrum. The shaped optical field was analyzed via cross correlation and frequency-resolved optical gating. The wave-packet evolution was analyzed by monitoring temporal interference via the optical Ramsey method to obtain both auto- and cross-interferograms of the engineered wave packet.

It is known that a quantum master equation that describes dissipative relaxation (such as spontaneous decay) can be separated in a part that describes spontaneous jumps and a jump-free part. The jump-free part of the evolution is determined by a non-Hermitian Hamiltonian H, which acts on state vectors, rather than on density operators. We identify a class of systems for which the complete evolution is entirely determined by the jump-free evolution, which is governed by H. Although this class is restricted, it contains a sizable number of systems of physical significance. Among these are two-, three-, and four-state atoms. The method is used to find explicit expressions of time-dependent expectation values in terms of the complex eigenvalues of H. As a first application we evaluate exactly the photon statistics in the driven Λ system. As a second example of the method, we treat the configuration of a V system driven by two standing waves. This system constitutes an effective beam splitter.

We present a cooling scheme based on interactions between atoms in different internal states and on energy shifts produced by external fields. The scheme predicts temperatures below the photon recoil limit without atomic losses. It can be considered as an alternative route to reach the conditions for Bose-Einstein condensation.

We numerically solve the time-dependent Schrödinger equation for a two-level atom interacting with an evanescent light field. The atom may be reflected or diffracted. Using the experimental parameter values we quantitatively model the evanescent field dopplerons (velocity-tuned resonances) observed by Stenlake et al. [Phys. Rev. A 49, 16 (1994)]. Besides successfully modeling the experiment, our approach provides complementary insights to the usual solution of the time-independent Schrödinger equation. We neglect spontaneous emission.

A recently formulated theory of high-order harmonic generation by low-frequency laser fields [Anne L’Huillier et al., Phys. Rev. A 48, R3433 (1993)] allows us to study the phase of the induced atomic dipole moment. We show that this phase exhibits a piecewise-linear dependence on the laser intensity. This dependence can be interpreted in quasiclassical terms, and is related to the action acquired by the electron during its motion in the laser field. The value of the phase, however, is also affected by the quantum effects of tunneling, diffusion, and interference. The phase of the dipole moment considerably influences the conversion efficiency, as well as the coherence properties, of the harmonics generated in macroscopic media.

We show that an approximate quantum-nondemolition measurement of the vibrational energy of a trapped ion in a standing wave may be made by monitoring the fluorescent intensity from a probe transition. The ac component of the mean photocurrent signal is directly proportional to the average vibrational quantum number. The power spectrum of the photocurrent also contains information on the vibrational energy. We show that the phase of the vibrational motion undergoes diffusion as expected for a quantum-limited measurement of the energy of oscillation.

In this paper we discuss the effect of scattered radiation generated by a gas of cold atoms on the temperature of the gas. We show that by treating the reradiated field of the atoms as a fluctuating background field we can derive a master equation for a single atom where the effect of the surrounding medium is included in an effective relaxation operator. This relaxation operator is of second order in the interaction with the medium and in the binary-collision approximation can be written as the sum of two-body interactions with a correlation time equal to the natural lifetime of the atomic transition. The effect of the medium on the two most important sub-Doppler cooling mechanisms, Sisyphus and motion-induced orientation cooling, is investigated analytically in a one-dimensional model. In this we restrict ourselves to the limit of low saturation, weak background field and take the rate-equation limit for the collision operator. We find that both mechanisms are very sensitive to such a background field and that the temperature increases approximately as the number of atoms to the one-third power.

Lasing without or with population inversion in a simple three-level atomic system has been analyzed by taking into account the effect of phase fluctuations in the driving field. An interesting phenomenon has been found: When the driving field is not very intense, a change from inversion laser to noninversion laser behavior can occur as the driving field linewidth increases.

We study the influence of quantum interference on the spontaneous emission from an excited two-level atom when either the atomic upper or lower level is coupled by a coherent field to a third, usually higher-lying, state. In the case of the upper level coupling, destructive quantum interference between two competing decay amplitudes produces a dark line in the emission spectrum, a phenomenon that should not be confused with the well known population trapping, and a narrowing of one of the two side lobes that make up the spectral profile. Quantum interference is absent, instead, in the case of the lower level coupling, and the spectrum modified by the external driving field is just the incoherent superposition of two Lorentzian lines. We suggest a physical interpretation of these results. In addition, we compare the analytic predictions of the simplest nontrivial versions of these models with more realistic but nonanalytic descriptions and show, numerically, that the interference effects persist in the upper level case even when additional complications are taken into account.

The quantum interference in the spontaneous-emission spectrum of a driven atom, when the upper level of the atomic transition is coupled to a third level via a classical driving field, results in a dark line in the absence of the atomic decays. The existence of the dark line is independent of the Rabi frequency associated with the driving field. There is no such dark line in the spontaneous-emission spectrum when, instead of the upper level, the lower level is coupled to a third level via a driving field. In this paper, we include the level decays, incoherent pumping, and the finite bandwidth of the driving field in our analysis and study their role in the spontaneous-emission spectrum in the two configurations.

We consider the simultaneous measurement of two conjugate variables by coupling the system of interest to two independent probe modes. Our model consists of linearly coupled boson modes that can be realized by quantum optical fields in the rotating-wave approximation. We approach the setup both as a device to extract observable information and to prepare an emerging quantum state. The initial states of the probe modes and the coupling are utilized to optimize the operation in the various regimes. In contrast to the Arthurs and Kelly ideal scheme [Bell. Syst. Tech. J. 44, 725 (1965)], our more realistic coupling does not allow perfect operation but the ideal situations can be approximated closely. We discuss the conditions for maximum information transfer to the probe modes, information extraction with minimum disturbance of the system mode, and optimal state preparation for subsequent measurements. The minimum disturbance operation can be made to approximate a nondemolition measurement, especially when the information is carried in one quadrature component only. In the preparation mode, we find that the recording accuracy of the probe signals plays an essential role. We restrict the discussion to the first and second moments only, but the method can easily be generalized to any situation. Choosing all modes to be in squeezed coherent states originally, we can carry out analytical considerations; other cases can be treated numerically. The results are presented and discussed in detail as the paradigm of a class of realizable measurements.

The electromagnetic field is quantized in dielectric media that show both loss and dispersion. The complex dielectric function of the medium is assumed to be a known function and the loss is modeled by Langevin forces in the forms of noise current operators. The noise current correlation function is related to the assumed dielectric function by the fluctuation-dissipation theorem. Field quantization is carried out for the infinite homogeneous dielectric, the semi-infinite dielectric, and the dielectric slab, where the fields in the second and third cases are restricted to propagation perpendicular to the dielectric surfaces. The forms of the vector potential operator are obtained in the different spatial regions for all three geometries, and in each case the required canonical commutation relation for the vector potential and its conjugate generalized momentum operator is verified. The spatial dependence of the vacuum field fluctuations is calculated for the two dielectric geometries that have surfaces.