The ${\mathrm{F}}^{5+}$(1s2s2${\mathrm{p}}^2$) ${}_{}{}^3{}_{}{}^{}\mathrm{D}$ and ${}_{}{}^1{}_{}{}^{}\mathrm{D}$ states formed by transfer excitation (TE) in 4.75–33.25-MeV collisions of Li-like ${\mathrm{F}}^{6+}$(1${\mathrm{s}}^2$2s) with He and ${\mathrm{H}}_2$ targets were studied using 0° Auger-electron spectroscopy. The TE cross sections for these states showed resonances around 20 MeV with an energy dependence well described by the resonant TE impulse approximation. Resonance excitation cross sections were extracted and found to be about 2.2 to 3.2 times larger than theory.

A correction to the nonrelativistic double differential Compton cross section within the framework of the impulse approximation is discussed. An expression for a first correction is found. The expression explains the asymmetry that is obtained in experiments where the Compton profile is measured.

Expressions for the three-body coefficients are derived by virial expansion of the zeroth and first moments of collision-induced spectra. For the ternary supermolecular complexes He-Ar-Ar, He-He-Ar, ${\mathrm{H}}_2$-He-He, ${\mathrm{H}}_2$-${\mathrm{H}}_2$-He, ${\mathrm{H}}_2$-${\mathrm{H}}_2$-${\mathrm{H}}_2$, and ${\mathrm{H}}_2$-Ar-Ar, these are evaluated numerically from first principles at a few temperatures between 50 and 300 K, using the most dependable induced-dipole and intermolecular potential functions available. Both rototranslational and rotovibrational bands are considered. Only the pairwise-additive contributions to the three-body induced-dipole moments are considered. Quantum corrections of the Wigner-Kirkwood type are given and found to be important. Strong three-body spectral components are predicted at the lower temperatures. The computed three-body spectral moments are compared with available laboratory measurements in the near- and far-infrared regions. At temperatures above 50 K, measured ternary moments are found to be consistently greater than calculated ones, especially at the higher temperatures. The excess may be due to a positive ternary spectral component of collision-induced absorption arising from nonadditive induced-dipole components of molecular triplets.

The spectra of Auger-like electrons of Kr have been studied in detail in the photon energy range of the 3$d_{3/2}$ and 3$d_{5/2}$→np (n=5,6,7,8) excitations. In addition to the 3$d^{\mathrm{-}1}$np→4$p^{\mathrm{-}2}$np spectator Auger-like lines the spectra show structures where the spectator electron is shaken up or down during the decay. Their contribution is found to increase in going to the excitations to higher Rydberg orbitals. Shake calculations are found to agree fairly well with the observed shake contributions.

Hyperfine-structure measurements in high 4$f^{12}$5d metastable levels of ${}_{}{}^{167}{}_{}{}^{}\mathrm{i}\mathrm{i}$ have been carried out to supplement earlier data on the low 4$f^{12}$6s levels. Ab initio multiconfiguration Dirac-Fock (MCDF) calculations have been performed, and the effects of core excitations and configuration interaction have been investigated. While good agreement between experiment and calculation was found for the low 6s levels, a less clear interpretation emerges from the higher 6d levels. This points directly to the problems in the MCDF scheme in understanding the effects of core excitation and configuration interaction.

The threshold behavior of the photodetachment cross section of negative ions as a function of photon frequency is usually described by the Wigner law. However, there is little theoretical guidance about the range or accuracy of the Wigner law. This paper reports the results of a model calculation using the zero-core-contribution (ZCC) approximation. Theoretical expressions for the leading correction to the Wigner law are developed, giving the range of validity of the Wigner law and the expected accuracy. The results, derived within the ZCC approximation, are relevant to extraction of electron affinities from experimental photodetachment data.

Pump and probe methods of laser spectroscopy were used to excite fluorescence from the E1 and F1 states of the HgZn excimer. Several bound-free and bound-bound fluorescence bands as well as excitation bands were recorded and correlated with a potential-energy diagram that includes the various spin-orbit components and supersedes the previously published potential-energy diagram based on Hund’s case-(a) coupling.

The photoionization cross section for the excited 7d state of atomic cesium has been calculated in the Hartree-Fock approximation. The results show excellent agreement with a recent measurement.

The double-photoionization probability of many-electron atoms is calculated within the independent-particle model. The sudden approximation approach and scaled hydrogenic wave functions are employed. The electron-electron interaction is effectively taken into account by screening parameters assigned to individual electrons. The interaction between the ejected electrons and other atomic electrons is described by the respective relaxation energies. The results for He and Ne agree well with the experimental data for photon energies greater than approximately twice the threshold energy.

Due to the increasing role that highly charged ions play in high-precision mass-ratio measurements within a compensated Penning trap, it is imperative that we investigate the dependency of the normal-mode frequencies on the total number of trapped charges. The experimental number dependency has been measured for four different ion species with various states of ionization. The absolute shift in both the observable cyclotron and magnetron frequencies is 0.018(3) Hz per equivalent electronic charge for a trap with characteristic dimension of 0.114 cm (in a 5-T field). The source of this systematic dependency has been traced to image charges induced on the surface of the trapping electrodes, whose electric field at the ion’s position near trap center is approximately linear in the displacement of the trapped ions. A simple spherical model has been developed that is useful as a guide in minimizing this systematic effect.

It has long been known that amplification will degrade an optical signal and will rapidly destroy any intrinsically quantum features that may have been associated with the input. However, devices that exhibit squeezed fluctuations in the gain or loss medium can reduce the detrimental effects of the inevitable amplifier noise. This makes it possible to retain nonclassical features (in particular squeezing) at higher levels of gain than is possible in conventional devices. In this paper we study the effect of these amplifiers on the photon-number fluctuations. We find that, for suitable inputs, phase-sensitive amplifiers can reduce the tendency for the photon-number distribution to spread and allow us to retain sub-Poissonian statistics at a higher level of gain than is possible in conventional devices.

We have applied the recently proposed beam-foil–laser method to determine lifetimes in multiply ionized atoms. The lifetimes of two levels in multiply ionized carbon have been measured. The results are, for C iii 2s3d ${}_{}{}^1{}_{}{}^{}D$, 0.15±0.01 ns and for C iv 3s ${}_{}{}^2{}_{}{}^{}S$, 0.21±0.02 ns. These values are in good agreement with the theoretical predictions. We have also determined these lifetimes using the classical (nonselective) beam-foil method. These latter lifetime results are in agreement with the beam-foil results reported previously but ≊20% longer than the beam-foil–laser values. The factors limiting the accuracy of the lifetime determinations by the beam-foil–laser method are discussed.

The third-order equations of motion for a bidirectional, inhomogeneously broadened ring laser at line center with backscattering are solved exactly when the additive noise terms are negligible. The resulting solution for the relative phase of the two propagating modes may exhibit steady-state or transient oscillations. For certain initial conditions, the solution is not unique and is unstable. This gives rise to deterministic phase jumps in both the transient and steady-state behavior. A series of phase jumps occurs if the system repeatedly crosses its unstable boundary. These series may be random or periodic if the system is driven by a stochastic or deterministic source, respectively. In all cases, the jumps are multiples of π radians in magnitude. The solution for the intensities provides a means to determine the pump parameter and backscattering coefficients for the laser through intensity measurements, provided the effects of spontaneous emission are negligible. The results are compared with numerical solutions of the original Langevin equations and with experiments.

We consider the small-signal response of a rate-equation laser to modulation of the laser cavity length. To avoid nonlinear resonances in modulators and power supplies, we demonstrate that one can hold the modulation frequency and amplitude fixed while varying the cavity detuning to change the resonant response of the laser to modulation, and thereby one can extract the relaxation oscillation frequency and the damping rate of those oscillations. This technique permits a careful study of the relaxation parameters of the laser that govern small oscillations and thereby permits discrimination among several different models recently proposed to describe ${\mathrm{CO}}_2$ laser dynamics. We demonstrate this method of analysis by applying it to such a laser experimentally with the result that the simple rate-equation model is shown to fail while the more complex vibro-rotational model satisfactorily describes the results.

Light-induced drift (LID) dynamics are studied in uncoated and silane-coated capillaries containing sodium and a few torr of neon or krypton. The adopted coating reduces the adsorption energy of the atoms at the surface of the cell by permitting the observation of wall frictionless LID. Moreover, it can be heated up to 200 °C, making it possible to work with saturated vapor over a wide range of densities. A measurement method of the drift velocity is proposed for the optically thin regime, and its dependence on the laser linewidth is observed using both a single-mode and a broadband laser. Drift velocities of up to 30 m/s are measured in a cell containing 6 Torr of krypton under broadband excitation.

Detailed studies of digitized recordings of periodic and chaotic intensity pulsing of an unidirectional far-infrared ${\mathrm{NH}}_3$ ring laser at 81.5 μm reveal common features of a broad range of different pulsing patterns as well as systematic relationships among entropies, dimensions, and decay rates of the autocorrelation function. Spiral-type ‘‘Lorenz-like’’ chaos of many different spiraling rates and of differing modulation depths has an underlying attractor dimension of 2.0–2.3 and an entropy rate that lies mainly in the range (0.2–0.7)$T^{\mathrm{-}1}$, where T is the average intensity pulsing period. Over a wide range of types of pulsing (spiral chaos, period-doubling chaos, and periodic states) the decay rate of the envelope of the autocorrelation function over short times provides an estimator of the entropy. The results are in excellent agreement with the characteristics of the Lorenz-Haken model for similar operating parameters.

The quantum noise properties of atomic and semiconductor lasers are compared. The intensity fluctuation spectrum of the output field is calculated for the case of regularly, i.e., sub-Poissonian, pumped lasers. The effects of spontaneous emission on the output amplitude fluctuations may be suppressed in regularly pumped atomic lasers by requiring the lifetime of the lower lasing level to be short in comparison with that of the upper laser level. The output amplitude fluctuations then tend to zero at the laser frequency. In regularly pumped semiconductor lasers, net stimulated emission of photons dominates over spontaneous emission because of the combination of pumping and rapid intraband thermalization due to Coulomb scattering.

The randomly stirred model of DeDominicis and Martin [Phys. Rev. A 19, 419 (1979)] is studied. It is shown from considerations of energy transfer that y=4 corresponds to the Kolmogorov model, when the wave-number (k) dependence of the stirring force is $k^{\mathrm{-}D+4\mathrm{}\mathrm{-}y}$, D being the dimensionality of space. It is seen that the correlation function has to be non-Lorentzian for y≠2-D, and hence the perturbation theory has to be a double-power series in y and D-2, in accordance with the recent calculation [Phys. Rev. A 36, 3322 (1987)] using the field-theoretic renormalization group. Amplitude ratios are calculated to the lowest order.

Accurate radial-distribution functions obtained from a thermodynamically consistent integral equation are used to calculate upper and lower bounds to the Helmholtz free energies of several inverse-power potential fluids and the Lennard-Jones fluid. Comparisons with results from Monte Carlo simulations indicate that the true free energies are tightly bracketed by the variational bounds. In addition, the simulations agree with the arithmetic mean of the limits near melt to within about 0.03${\mathrm{Nk}}_B$T for inverse power fluids and about 0.06${\mathrm{Nk}}_B$T for Lennard-Jones fluids. These results indicate that it is possible to obtain accurate free energies very efficiently by the variational method.

The hypernetted-chain (HNC) approximation is applied to study the critical behavior of a Lennard-Jones mixture. The parameters of the model potential are appropriate to describe a He-Xe mixture in the thermodynamic region where ‘‘gas-gas phase separation’’ is known to occur. The locus of points in the temperature-concentration plane where the k→0 limit of the concentration-concentration structure factor $S_{\mathrm{cc}}$(k) diverges, i.e., the spinodal line, is determined through an extrapolation of the HNC results from the region where this integral equation is solvable, toward the phase stability boundary, where the algorithm becomes highly unstable and no solution can be found. The extrapolation is based on a power-law behavior of $S_{\mathrm{cc}}$(0) that is verified to hold in the realm of the available results. The critical temperature and concentration so obtained compare quite favorably with the experimental data.