A free-parameter linear-combination-of-atomic-orbitals approach is presented for analyzing the stopping power of slow ions moving in a metal. The method is applied to the case of He moving in alkali metals. Mean stopping powers for He present good agreement with local-density-approximation calculations. Our results show important variations in the stopping power of channeled atoms with respect to their mean values.

Kβ spectra of heliumlike iron, Fe xxv, have been observed from tokamak-fusion-test-reactor (TFTR) plasmas with a high-resolution crystal spectrometer. The wavelength range of the Fe Kβ spectrum partially overlaps the spectrum of heliumlike nickel (Ni xxvii), which is used on TFTR and the joint European torus for ion-temperature measurements. The experimental arrangement made it possible to observe the Fe xxv Kβ lines and their satellite transitions of the type 1s2l’3l’’→1${\mathit{s}}^2$2l’, as well as the entire satellite spectrum of the Ni xxvii Kα line simultaneously. In order to identify the features of the Kβ spectra and to study their possible interference with the Ni xxvii spectrum, the intensity of the Kβ spectrum was enhanced by the injection of iron into the plasma. Accurate wavelengths and intensities have been obtained and compared with different theoretical calculations.

Wavelengths and isotope shifts have been measured for the 1738.4-, 1738.5-, 1740.2-, and 2354.2-Å lines of Hg iii with an uncertainty of 0.002 Å. The lines were excited in a pulsed radio-frequency discharge and observed with a 10.7-m normal-incidence vacuum spectrograph. Observations were made with lamps containing natural Hg, ${}_{}{}^{198}{}_{}{}^{}\mathrm{Hg}$, and ${}_{}{}^{204}{}_{}{}^{}\mathrm{Hg}$. By using well-established relative isotope shifts, wavelengths of these four lines for ${}_{}{}^{196}{}_{}{}^{}\mathrm{Hg}$, ${}_{}{}^{200}{}_{}{}^{}\mathrm{Hg}$, ${}_{}{}^{202}{}_{}{}^{}\mathrm{Hg}$, and the centers of gravity for ${}_{}{}^{199}{}_{}{}^{}\mathrm{Hg}$ and ${}_{}{}^{201}{}_{}{}^{}\mathrm{Hg}$ were also determined. The results provide important data for determining elemental and isotopic abundances of Hg from spectra of Hg-rich chemically peculiar stars.

Core-excitation spectra at the carbon K threshold of methane, ethane, and propane, as well as of the deuterated molecules, were studied by high-resolution photoabsorption using synchrotron radiation from the SX700/II monochromator at BESSY. The spectra contain signals from excitations to C 1${\mathit{s}}^{\mathrm{-}1}$np Rydberg states and their vibrational substates, as well as from transitions to C 1${\mathit{s}}^{\mathrm{-}1}$ns Rydberg states. The latter excitation is dipole forbidden in methane, but rendered possible by strong vibronic coupling. Transitions to vibrational substates could be identified via the observed isotope effects. The C 1${\mathit{s}}^{\mathrm{-}1}$np Rydberg states were found to be split by a Jahn-Teller effect or by molecular-field interaction. C-H and C-C equilibrium distances as well as vibrational frequencies in the core-excited molecular states were derived within the Franck-Condon model from the vibrational fine structures of the C 1${\mathit{s}}^{\mathrm{-}1}$3p Rydberg excitations.

The spectrum of iodine was photographed in the 300–2000-Å wavelength region on a 3-m normal-incidence spectrograph. The source used was a triggered spark. The previously reported analysis of I iii was found to be completely erroneous. All levels of the ground state 5${\mathit{s}}^2$5${\mathit{p}}^3$ and all but three levels of the three excited configurations 5s5${\mathit{p}}^4$, 5${\mathit{s}}^2$5${\mathit{p}}^2$5d, and 5${\mathit{s}}^2$5${\mathit{p}}^2$6s have been established. 117 lines have been classified in this spectrum. Configuration-interaction calculations involving the 5s5${\mathit{p}}^4$, 5${\mathit{s}}^2$5${\mathit{p}}^2$6s, 5${\mathit{s}}^2$5${\mathit{p}}^2$5d, and 5${\mathit{s}}^2$5${\mathit{p}}^2$6d configurations describe the observed spectrum quite satisfactorily.

The collisional-broadening and -shift rate coefficients (${\mathit{k}}_{\mathrm{br}}$ and ${\mathit{k}}_{\mathrm{shift}}$), for both helium and argon buffer gases, have been measured in the impact limit for the 6${\mathit{s}}^2$ ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$→6s6p ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$ intercombination transition of barium. Detailed absorption line shapes were measured at three different ground-state number densities by monitoring the transmitted intensity of a weak cw probe laser as it was scanned over the transition. A single, density-independent line shape was then constructed and fit to a sum of Voigt functions (to account for hyperfine structure and isotope shifts) in order to determine the broadening and shift rates. By repeating the process for several buffer-gas pressures, ${\mathit{k}}_{\mathrm{br}}$ and ${\mathit{k}}_{\mathrm{shift}}$ were determined from least-squares straight-line fits to the broadening and shift rates versus buffer-gas number density. Absolute normalization of the line-shape data was used to provide accurate ground-state column densities. Column-density information was then combined with measurements of white-light-absorption equivalent widths for the 6${\mathit{s}}^2$ ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$→6s6p ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ resonance transition to yield broadening rates for that transition. These values for the resonance line lie between previous literature values, which are widely discrepant. Finally we measured the absolute metastable 6s5d ${}_{}{}^3{}_{}{}^{}$${\mathit{D}}_2$ column density under conditions of optical pumping through the ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$ level, and determined that, in steady state, even with a weak cw pump laser, ∼20% of all barium atoms in the vapor could be found in the ${}_{}{}^3{}_{}{}^{}$${\mathit{D}}_2$ level (with approximately 60% spread over the full ${}_{}{}^3{}_{}{}^{}$${\mathit{D}}_{\mathit{J}}$ metastable manifold).

Exact amplitudes for the scattering of an electron on the zero-range potential in a magnetic field are analyzed as functions of a complex energy variable. Trajectories of the poles on various sheets of the Riemann surface are studied. Physically important resonances are identified and analytic estimates predicting their characteristics are presented. Transmission and reflection probabilities are calculated and related to the study of the resonances.

Rydberg atoms in external electric and magnetic fields have recently emerged as atomic-scale laboratories where the quantum mechanics of classically nonintegrable systems can be studied. In this article we show, using classical canonical perturbation theory, how the intricate nonlinear dynamics of a Rydberg electron in crossed electric and magnetic fields can be described in terms of two coupled asymmetric tops.

A pulsed metastable argon beam is transversely cooled in one dimension via the closed 4s[11/2${]}_2^{\mathit{o}\mathrm{-}}$4p[21/2${]}_3$ transition. A standing light wave, orthogonal to the atomic beam and located just at the source, provides the cooling. In all the measurements, the maximum electric field is equivalent to a Rabi frequency of ∼220 natural linewidths. The enhancement of the metastable atom flux is measured as a function of the interaction time with a time-of-flight technique. The dependence on the laser detuning is investigated and compared with theory.

It is shown how to obtain efficiently quantum-mechanical tunneling rates (and energy shifts) induced by electric fields for arbitrary polyelectronic states. The problem is formulated as one of solving nonperturbatively a complex-eigenvalue matrix equation, constructed in terms of two separately optimized multidimensional function spaces, Q and P. The theory is demonstrated on two prototypical ground states, He 1${\mathit{s}}^2$ ${}_{}{}^1{}_{}{}^{}$S and Li 1${\mathit{s}}^2$2s ${}_{}{}^2{}_{}{}^{}$S, as well as on the Li 1${\mathit{s}}^2$ 2p ${}_{}{}^2{}_{}{}^{}$P° excited levels (${\mathit{M}}_{\mathit{L}}$=0,±1). For example, for field strengths F=3.86×${10}^7$–3.86×${10}^8$ V/cm the He ${}_{}{}^1{}_{}{}^{}$S tunneling rates range from 5.79×${10}^7$ to 7.75×${10}^{10}$ ${\mathrm{s}}^{\mathrm{-}1}$.

We have measured the alignment of Hg(6 ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$) atoms following off-resonant excitation of the Hg 6 ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}$–6 ${}_{}{}^3{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$ transition in the presence of Kr. We present a polarization spectrum for both red and blue wings out to detunings beyond 100 ${\mathrm{cm}}^{\mathrm{-}1}$. This represents a considerable extension to the existing results, which has been made possible by the use of a pump-and-probe excitation scheme. In the experiment a pulsed laser, detuned from the resonance, creates an alignment in the upper state. This is probed by tuning a delayed second laser to a higher transition and monitoring laser-induced fluorescence from the two-step process. The alignment of the asymptotic Hg(6 ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_1$) atoms is determined by comparison of the signals obtained for different relative polarizations of the lasers. We discuss the advantages of this method and the relation of the raw data to the polarizations presented. The results are discussed within the context of a simple quasiclassical model of the process.

The connection between the hydrogen atom in a generalized van der Waals potential and the notion of local and normal modes is investigated analytically and numerically. It is found that the dynamics in the hydrogenic case can be classified as local, normal, or precessional normal in a similar way to the spectroscopic description of degenerate vibrational states of a molecule. Semiclassical quantization of the system is discussed.

Using the method of B-spline expansion, we calculate on a VAX-11/785 computer an extensive energy structure of hydrogenic circular states in a uniform superstrong magnetic field (magnetic quantum number ‖m‖=21–40, field strength up to 470 T). Our calculations quantitatively confirm previous results obtained by Wunner, Kost, and Ruder [Phys. Rev. A 33, 1444 (1986)] for selected m values and a smaller range of fields. A formula has been found to describe the dependence on m of the maximum radiative lifetimes of the circular states with negative m values. The effectiveness of the B-spline method in treating the hydrogenic atom in a magnetic field is further illustrated.

We consider nonclassical properties of the field at the output of an amplifier under the operational condition that the output exhibits neither squeezing nor sub-Poissonian statistics but has the nonclassical P function. We also present explicit results for the output P function when the input is strictly a quantum-mechanical state similar to a Fock state. The nonclassical properties of the marginal distribution associated with the output are derived. The domain where the marginal distribution remains nonclassical is different from the domain over which the output P function is nonclassical. The amplifier is shown to be a useful device for direct measurements of the quasiprobabilities.

In this paper, we have investigated the influence of the counter-rotating terms on the squeezing of light in the two-photon Jaynes-Cummings model by means of the nonrelativistic QED. We verified that the effect of the virtual-photon field increases the squeezing. The relations between the degree of squeezing and the frequency of field, the mean photon number, and the atom-field coupling constant have also been analyzed.

A spectral analysis is given of the quantum fluctuations in an optical interferometer to detect gravitational radiation. Two different methods of beating the standard quantum limit are examined: directing a squeezed state into the nonlaser input port of the interferometer and placing a Kerr medium into both arms of the interferometer. For both the Kerr medium and large squeezing cases the interferometer system is limited ultimately by the damping noise in the mirrors, not by noise in the light.

We give a direct method for obtaining exact solutions of the modified nonlinear Schrödinger equation ${\mathit{iu}}_{\mathit{t}}$+ε${\mathit{u}}_{\mathit{x}\mathit{x}}$+2p‖u${\mathrm{\Vert }}^2$u+2iq(‖u${\mathrm{\Vert }}^2$u${)}_{\mathit{x}}$ =0 describing the propagation of light pulses in optical fibers. By using a suggestive particlelike description, we classify all the obtained analytical solutions into one of the following categories: the ‘‘algebraic’’ soliton, the one-soliton solution, the bright solitary waves, and the regular periodic solutions which are very important from the physical point of view.

We consider a Λ-type three-level atom interacting simultaneously with two quantized cavity fields and a classical field, all of different frequencies. The classical field is of constant amplitude and the quantized cavity fields are dynamical variables. The effective interactions are Raman type with the two cavity fields regarded as Stokes and anti-Stokes modes. The classical field acts as the pump-mode, so that both the pump–Stokes and the pump–anti-Stokes transitions are included. We present analytic expressions for the dressed states of the system in a general situation where the two channels have different coupling strengths. The dressed states are closely related to the two-mode squeezed number states. We find that two-mode squeezing and nontrivial phase correlation occur in the model. The effects of weak cavity damping are also discussed.

We have measured the absorption from a weak time-delayed probe field by a two-level atomic system [Na 3${\mathit{s}}_{1/2}$(F=2,${\mathit{m}}_{\mathit{F}}$=2)→3${\mathit{p}}_{3/2}$(F=3,${\mathit{m}}_{\mathit{F}}$=3)] saturated by a phase-diffusing pump field. The pump and probe, derived from the same artificially-noise-modulated phase-diffusing laser beam, are frequency degenerate and resonant with the atomic transition. The probe is a time-delayed replica of the pump. Our results, carried out in a regime where the field bandwidth and the Rabi frequency are comparable, provide confirmation of recent theoretical predictions [K. Gheri, M. A. M. Marte, and P. Zoller, J. Opt. Soc. Am. B 5, 1559 (1991)] for the atomic response to the non-Markovian composite of a pump and time-delayed probe, valid for arbitrary bandwidths and intensities. Amplification of the probe field is observed for delays comparable to the lifetime of the upper level and again for very long delays, if the bandwidth is less than the decay rate of the upper state.

The suppression of forward-propagating stimulated hyper-Raman (SHR) emission is well studied in sodium vapor. Theory predicts that SHR emission to a state linked to the gound state by a one-photon transition is suppressed by an interference with a four-wave-mixing (FWM) emission that links that state to the ground state. Since FWM emission only propagates in the forward direction due to phase-matching considerations, only the forward SHR emission is suppressed. This has been previously demonstrated in sodium. An obvious corollary to this theory is that no suppression occurs if the state is not linked to the ground state by a one-photon transition. A serendipitous arrangement of energy levels in cesium allowed this corollary to be tested and confirmed here.