We study the near-resonant dipole-dipole interaction between two atoms in a broadband squeezed vacuum. We show that this ‘‘vacuum’’ modifies the rate of spontaneous emission of the atoms so that it may depend not merely on their relative position, as is normally the case, but also on their center-of-mass position. The explicit form of this latter dependence is a function of the way squeezing is achieved. We also show that in contrast to the spontaneous decay rate, squeezed vacua do not modify the dipole-dipole potential between the atoms as compared to its usual form. Finally, we develop a Monte Carlo wave-function description of the interaction between atoms with an arbitrary internal structure and a squeezed vacuum and apply this formalism to the case of off-resonant excitation of the atoms. We find that in addition to the usual light shift, the squeezed vacuum results in an additional contribution to the effective potential governing the evolution of the atomic ground states. © 1996 The American Physical Society.

The phase relationship between an induced atomic dipole moment and a driving laser field is an essential aspect of high harmonic generation (HHG) in a dense medium. A ‘‘phase-matching’’ criterion must be fulfilled to obtain coherent amplification of harmonic radiation, which is critical for practical HHG. We have performed numerical calculations on model atoms to survey the intensity dependence of the phase in the case of strong one- or two-frequency laser fields. The calculations show that multiphoton resonances significantly affect the yield of harmonic generation and that in the ‘‘plateau’’ regime, the phases exhibit only weak dependence upon the intensity of the driving field. ©1996 The American Physical Society.

We study the spontaneous-emission of a single atom located between two parallel infinite plates where one of the plates is partially reflective and the plate separation is of the order of the wavelength of the atomic transition. We pay particular attention to the nature of the field modes in such a finite finesse cavity, including the full three-dimensional nature of the field. We then compute the decay rate of an excited atom placed inside such a cavity. The angular distributions of the spontaneous-emission and of the cavity field vacuum fluctuation variances are investigated. Finally, we examine the output field from an atom inside a finite finesse microcavity. We show that the radiation transmitted outside such microcavity forms a nondiffracting Bessel beam. © 1996 The American Physical Society.

We investigate the dynamics of a two-mode stimulated Raman scattering model including propagation and the quantum correlations that develop between the Stokes and anti-Stokes fields. For example, under certain conditions two-mode squeezed states can result. We report results for quadrature squeezing and sum squeezing. Quadrature squeezing only occurs when the anti-Stokes coupling constant is larger than the Stokes coupling constant. The amount of squeezing increases as the damping of the material polarization is increased. © 1996 The American Physical Society.

Based on a microscopic theory of a two-band semiconductor light amplifier, we show that plasma heating, cooling, and ultrafast memory effects all act in concert to produce strong distortion of subpicosecond pulses propagating in semiconductor amplifiers. Plasma heating, spectral hole burning, and carrier density depletion are responsible for saturation of the gain seen by a propagating intense femtosecond pulse in the amplifier. Plasma cooling replenishes the carrier population on the trailing edge of the pulse, leading to pulse broadening as a consequence of gain regeneration. The inclusion of memory effects in the description of dephasing processes goes beyond the usual Markov assumption of constant dephasing rates; it significantly affects the dynamical pulse reshaping processes. © 1996 The American Physical Society.

A different way of producing antibunched light was experimentally demonstrated in which the production process is difficult to understand by a naive photon picture. A degenerate beam of down-converted photon pairs from a nonlinear crystal pumped by pulsed light was mixed with coherent local oscillator pulses by a beam splitter, and the intensity autocorrelation of one of the output beams was measured. It showed two-photon interference fringes as the phase difference of the two input fields was varied, and showed antibunching when the interference was destructive. © 1996 The American Physical Society.

We have measured the gain and statistical-noise properties of a weak probe beam amplified through two-beam coupling in atomic-potassium vapor for both the Rabi and stimulated Rayleigh gain features. The probe-beam gain was observed to be as large as 125 for the Rabi feature, whereas the gain was typically less than 2 for the Rayleigh feature. The rms noise at the Rabi gain feature was approximately three times greater than the ideal amplifier quantum-noise limit. For the Rayleigh gain feature, the rms noise was 12 to 15 times greater than the ideal amplifier quantum-noise limit. We present a fully quantum-mechanical theory of two-beam coupling in a system of two-level atoms which includes the effects of atomic motion and pump-beam absorption. The predictions of this theory are in good agreement with the experimental data. © 1996 The American Physical Society.

We consider the interaction of a two-level atom with a squeezed vacuum, both in free space and in a cavity of moderate Q. In the latter case, only vacuum modes coupled to the cavity are squeezed. In both cases we calculate the following quantities for the fluorescent light fields: the second-order intensity correlation function ${\mathit{g}}^{\mathrm{}\left(2\right)\mathrm{}}$(τ), the spectrum of squeezing, the coherent spectrum, and the spectrum obtained in a pump-probe absorption measurement. Nonclassical behavior is discussed and comparison to an ordinary vacuum and thermal fields is made. © 1996 The American Physical Society.

Using only 40 J of drive energy in a 650-ps main pulse we demonstrated lasing on the J=0→1, 3p→3s transition in neonlike titanium at 32.6 nm. This is an order of magnitude smaller drive energy than has been used previously to drive low-Z neonlike x-ray lasers. We present a series of experiments using titanium slab targets which study the threshold for lasing in neonlike titanium when the 1.8-cm-long targets are illuminated by a low-intensity prepulse 5 ns before the main optical drive pulse of the 1.05-μm Xingguang Nd-glass laser. For a 1% prepulse, the energy threshold is measured to be 40 J, which contrasts with 110 J for a 9% prepulse. In both cases, the 32.6-nm Ti lasing line peaks 5 mrad off-axis with divergences of 4 and 5 mrad for the 1% and 9% prepulse cases, respectively. © 1996 The American Physical Society.

We consider nonlinear selective reflection on the interface between dielectric media and dilute vapors of three-level atoms. Assuming a pump-probe scheme with cascade-type excitation, we study the modification ΔR of the reflection coefficient of the probe induced by the presence of the pump. We extend previous calculations of the frequency spectrum of ΔR made for low probe power to the case of arbitrary probe power. One then obtains a strong resonance which has already been observed experimentally. Moreover, for the two-photon resonance present in the low-intensity spectrum, a power splitting can be predicted with increasing intensity © 1996 The American Physical Society.

Indirect path methods, viz., the staircase and the ladder methods of Levy et al. [Phys. Rev. A 36, R249 (1987)], have been employed to estimate the nonrelativistic ground-state energies of neutral atoms He-Ar, within the local-exchange prescription of Harbola and Sahni. We demonstrate that the total atomic energies thus estimated are comparable to their Hartree-Fock staircase counterparts and become superior to the latter for Z≥8. © 1996 The American Physical Society.

A method is introduced that allows the construction of pseudopotentials in the density-functional theory. This method is based on a procedure worked out by one of the authors [J. Phys. B 26, 43 (1993); Philos. Mag. B 69, 779 (1994)] for determining Kohn-Sham potentials, one-electron orbitals, and energies from the electron density. The Hartree-Fock densities of Bunge, Barrientos, and Bunge [At. Data Nucl. Data Tables 53, 114 (1993)] are used to obtain the Kohn-Sham potentials of the Li, Na, and K atoms, and then Phillips-Kleinman-type [Phys. Rev. 116, 287 (1959); 118, 1153 (1960)] pseudopotentials are calculated. The arbitrariness of the pseudo-orbital is removed by minimization of the kinetic energy. © 1996 The American Physical Society.

Based on functional expansions developed recently, transition functional method is introduced. This method can be considered a functional generalization of Slater’s transition-state method. It can be used to calculate energy differences accurately. © 1996 The American Physical Society.

The static quadrupole moments and polarizabilities of ${\mathrm{B}}^{\mathrm{-}}$, ${\mathrm{C}}^{\mathrm{-}}$, and ${\mathrm{O}}^{\mathrm{-}}$ are calculated using many-body perturbation theory and coupled-cluster methods. Results obtained for the ${\mathit{C}}_{\mathit{zz}}$:zz polarizability components for these anions, at the highest level of approximation [double substitution coupled cluster (CCD) plus single and triple CCD], are, respectively, 1.24×${10}^4$, 0.99×${10}^3$, and 4.15×${10}^2$ a.u. As regards the quadrupole moments, the results obtained are 13.02 a.u. for ${\mathrm{B}}^{\mathrm{-}}$ and 3.69 a.u. for ${\mathrm{O}}^{\mathrm{-}}$. The role of correlation effects is discussed at various levels of approximation. © 1996 The American Physical Society.

The double-capture processes involved in the ${\mathrm{B}}^{4+}$(1s)+He(1${\mathit{s}}^2$) collision have been calculated by means of an ab initio configuration-interaction method followed by a semiclassical dynamical treatment. The results are compared to previous theoretical works in order to analyze the adequacy of model potential approaches. © 1996 The American Physical Society.

We apply two different methods to the calculation of the triply differential cross section (TDCS) for double ionization of helium. In one method, the 3C method, the final state is described by a product of 3 Coulomb continuum wave functions, while in the other method, the 2SC method, the final state is described by a product of 2 screened Coulomb wave functions employing effective charges. We present results at the energies and geometries covered in the recent experiment by Lablanquie et al. [Phys. Rev. Lett. 74, 2192 (1995)]. There are substantial discrepancies. We also comment on a recent measurement of the absolute TDCS by Schwarzkopf and Schmidt [J. Phys. B 28, 2847 (1995)]. The measured result, as originally reported, is a factor of two smaller than the value for the absolute TDCS calculated using the 2SC method. We discuss this discrepancy. © 1996 The American Physical Society.

We show that the transverse spatial coherence of the atomic density matrix is destroyed to some extent by the deflection of the atom from an off-resonant quantized standing-wave field. The collapse and revival of the atomic spatial coherence are demonstrated. © 1996 The American Physical Society.

Resonantly enhanced multiphoton ionization of xenon near the three-photon 6s resonance has been studied under the excitation by the Bessel beams. It has been shown that the ionization spectra are significantly different in the cases of the Bessel and the Gaussian laser beams. This difference is caused by an internal third-harmonic field, which in the Bessel beam is generated in a wide spectral range due to the self-phase-matching mechanism. The cancellation of the 6s resonance in the Bessel beam has been demonstrated. Similar to the case of the Gaussian beams the canceled resonance appears in the spectra under the excitation by counterpropagating Bessel beams. The origin of some features in the ionization spectra is discussed. © 1996 The American Physical Society.

The dynamic decoupling of the correlation function hierarchy under the general quadratic Hamiltonian is exploited to extend the results obtained for coherent pumping and squeezing in Ref. . Closed c-number dynamic equations are given explicitly for three- and four-operator averages, for an arbitrary (pure or mixed) initial state of the field. At this level an independent c-number constant of motion appears, related to two-photon correlation properties of the initial state. Extension to higher correlation functions is straightforward. © 1996 The American Physical Society.

The interaction of the electromagnetic field with lossless Lorentz oscillators modeling the inhomogeneous dielectrics is diagonalized in a closed Fabry-Pérot resonator using the generalized polariton transformation. Resulting dispersion relations coincide with the classical ones obtained by the solution of the wave equation. The corresponding decomposition is, however, orthogonal and complete in the enlarged Hilbert space. © 1996 The American Physical Society.