The isometry U${\mathrm{^}}^{\mathrm{°}}$,U${\mathrm{^}}^{\mathrm{°}}$U^≠U^U${\mathrm{^}}^{\mathrm{°}}$=1^, which relates the ideal phase measurement to the feasible phase measurement based on heterodyne detection, is specified here. Consequently, the Shapiro-Wagner phase measurement [IEEE J. Quantum Electron. QE-20, 803 (1984)] incorporates the ideal phase concepts of Susskind-Glogower [Physics 1, 49 (1964)] or Pegg-Barnett [Phys. Rev. A 39, 1665 (1989)].

In view of a recent paper [F. Michelot, Phys. Rev. A 45, 4271 (1992)] tackling the Hamiltonian of an arbitrary number of harmonically coupled oscillators, we present a coordinate representation of the unitary operator that can diagonalize the Hamiltonian. The normally ordered form of the unitary operator, which manifestly connects two Fock spaces associated with the uncoupled and coupled oscillators, is also derived by virtue of the technique of integration within an ordered product of operators.

We have constructed a gradient-corrected exchange functional which, when used in a self-consistent Kohn-Sham procedure, gives the exact Schrödinger energy and density for the hydrogen atom. The functional bears very little resemblance to any of the commonly used exchange functionals, even in its asymptotic behavior.

The second-order Born cross sections of positronium formation are calculated for positron-hydrogen collisions in the energy region below 100 eV and compared with the recent measurement of Sperber et al. [Phys. Rev. Lett. 68, 3690 (1992)]. Better agreement is achieved above 25 eV than other existing theoretical values including elaborate close-coupling calculations. This result implies that continuum states that are not taken into account fully in other theoretical calculations are contributing significantly to positronium formation through a second-order process.

Distorted-wave calculations of the triply differential cross sections for electron-impact ionization of Li and Mg are presented for the coplanar, ${\mathrm{\theta }}_{12}$=π geometry in which the final-state electrons share 2 eV of excess energy equally. Our theoretical approach, described in detail elsewhere [C. Pan and A. F. Starace, Phys. Rev. A 45, 4588 (1992)], employs a partial-wave expansion of initial- and final-state wave functions, treats direct and exchange interactions of initial and final electrons with the target core, and treats the final-state interaction between the two continuum electrons by a screening potential. Li and Mg targets are found to have more complex (e,2e) angular distributions than either H or He targets, stemming in large part from significant p-wave and higher one-electron phase shifts in the former elements.

A recent paper by Golser and Semrad [Phys. Rev. Lett. 66, 1831 (1991)] showed a departure from velocity proportionality in their energy-loss measurement of a hydrogen projectile in the gas below 20 keV. We point out that their result is a consequence of complex collision dynamics that is common in the molecular regime and has been known for some time among atomic physicists. The observation is well reproduced by a compilation of published stopping cross sections.

An examination is presented of the adequacy of the frequently used incoherent scattering function S(x,Z) for an explanation of available semiconductor detector results concerning atomic Compton-scattering cross sections at small momentum transfer. The conclusion is that the underlying simple theoretical treatment of electron-binding effects has not been accurately tested so far on account of insufficient energy resolution of the reported experiments.

The production of binary-encounter electrons in collisions of ${\mathrm{C}}^{\mathit{q}+}$ ions with molecular hydrogen has been studied at an impact energy of 0.75 MeV/amu. The measured double-differential cross section (DDCS) at a forward angle (${\mathrm{\theta }}_{\mathrm{lab}}$=0), with respect to the beam direction, is in excellent agreement with the theoretical cross sections evaluated in the impulse approximation by using the elastic-electron–ion differential cross section with the Compton profile of the target electrons. The theoretically calculated DDCS is extremely sensitive to the impact energy. Hence a precise measurement of the projectile beam energy is required to compare predicted values with the data. The agreement between theory and experiment demonstrates the importance of exchange in the description of binary-encounter electrons and that the exchange increases with the number of electrons on the projectiles.

We report on the effect of the spatial inhomogeneity of the assisting infrared radiation on the two-frequency photodetachment of ${\mathrm{H}}^{\mathrm{-}}$. We find that the curves showing the photodetachment cross section as a function of the frequency change their slope at a frequency which depends on the degree of the spatial inhomogeneity of the infrared illumination.

The statistical fluctuations of a single-mode laser with correlations between additive and multiplicative white-noise terms are investigated theoretically. The mean, variance, and skewness of the steady-state laser intensity are calculated through a one-dimensional laser equation. Compared with a laser model of independent noises, the fluctuation appearing in the laser field is much larger.

The overall-permutation-symmetry property of the nonlinear optical hyperpolarizabilities in a nondissipative medium is examined to find that the time-reversal symmetry is already assumed in the Manley-Rowe power relation, a basic relation adopted in the derivation of the overall permutation symmetry. This indicates that the overall permutation symmetry is a consequence of the time-reversal symmetry. The quantum-mechanical expression of hyperpolarizability is shown to satisfy both the overall permutation and the time-reversal symmetry explicitly. From the extended symmetry relation, it is predicted that second-harmonic generation and difference-frequency generation, two different nonlinear optical processes, are governed by the same parameter.

Milburn has recently proposed a model [Phys. Rev. A 44, 5401 (1991)] in which quantum states evolve into statistical mixtures of stationary states. One might think that this would imply that any observable quantity would become independent of time. We argue that, on the contrary, the decoherence implied by Milburn’s model would have no observable effect at all.

Finkelstein’s criticism [Phys. Rev. A (to be published)] of my paper [Phys. Rev. A 44, 5401 (1991)] presupposes time measurements of an accuracy explicitly ruled out in the paper.

This paper prescribes an orbital construction of the exact local effective potential in the Kohn-Sham self-consistent equations, so that from a given electron density the corresponding exact Kohn-Sham potential and orbitals may be found self-consistently. It also shows the convergence of the method if the system is v representable.

We report a study of charge transfer from laser-aligned Rydberg atoms in collisions with ${\mathrm{Ar}}^{+}$ ions in the velocity-matching regime. The Rydberg atoms in well-defined magnetic substates were prepared by two-photon laser optical pumping in a weak magnetic field. The results are compared with classical-trajectory Monte Carlo calculations and can also be understood in terms of a simple and ‘‘intuitive’’ picture.

Measurements of relative dielectronic recombination (DR) cross sections for fluorinelike xenon (${\mathrm{Xe}}^{45+}$) are presented. Recombination takes place in an electron-beam ion trap, where decay rates are obtained as the ions recombine with beam electrons. Experimental data are obtained by counting the number of ions that remain, as a function of time, following the recombination period. The counting is accomplished through the use of an ion-extraction system. An ultralow beam current, 2 mA, was used to obtain an energy resolution of 10.6 eV full width at half maximum. The experimentally measured resonances are compared to convolved theoretical DR resonance strengths. The agreement with theory is excellent.

The response function of alkali-metal clusters, modeled as jellium spheres, to dipole (L=1) and quadrupole (L=2) spin-dependent fields is obtained within the time-dependent local-spin-density approximation of density-functional theory. We predict the existence of low-energy spin modes of surface type, which are identified from the strength function. Their collectivity and evolution with size are discussed.

We calculate fully correlated time-dependent two-electron wave functions for a one-dimensional analog of ${\mathrm{H}}^{\mathrm{-}}$ exposed to a short strong-field laser pulse. The onset of two-electron stabilization is identified with an inactive core electron at intensities around ${10}^{13}$ W/${\mathrm{cm}}^2$ for moderate-frequency (2 eV) laser light. Conventional one-electron stabilization is found at much higher intensities and frequencies.

The use of a very simple technique of proportional feedback is proposed to stabilize an optical bistable system on the entire middle branch of its steady-state characteristic without otherwise altering the system. The conditions of stabilization are analyzed and the efficiency of the method is experimentally demonstrated.

Using classical dynamics we analyze the ionization of the maximum angular-momentum circular Rydberg orbits of the hydrogen atom in strong circularly polarized microwave radiation. We find the ionization threshold generally higher than that for the static field, depending upon the direction of rotation, and in some cases completely different than the prediction based upon the above barrier escape. Below the ionization threshold the system returns to its initial state after interacting with the smooth microwave pulse.