We have examined the laser ionization of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ using 1.053-μm 1.5-ps laser pulses. The use of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ rather than ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ in the experiment enables the detection of the second charge state separately from a troublesome background contaminant ${\mathrm{H}}_2^{+}$. In these experiments, the production of doubly charged ions is dominated by the sequential process rather than by the direct or simultaneous process.

We have calculated partial cross sections for photoionization of helium in the 2 ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}^{\mathit{e}}$ metastable state above the n=2 threshold. In this process, most of the ${\mathrm{He}}^{+}$ ions remain in an n=2 excited state so that interactions involving the degenerate n=2 open channels can be more easily studied. Our results show that an enhancement of the resonance structures is observed in both total and n=2 partial cross sections with respect to ground-state photoionization. The origin of this effect is discussed in detail.

The normal method for calculating very precise eigenvalues for ${\mathrm{H}}_2$ and its isotopes is to solve the Schrödinger equation using a reduced mass calculated from the bare nuclear mass with the mass-independent Born-Oppenheimer potentials and with mass-dependent adiabatic and nonadiabatic correction terms that account for the finite mass of the nuclei. On the other hand, scattering calculations have used reduced masses calculated from the masses of the separated atoms to solve the Schrödinger equation with mass-dependent adiabatic potentials, but with no explicit treatment of electronically off-diagonal nonadiabatic corrections. We have extended the conventional bound-state methods based on bare nuclear masses into the continuum by introducing an effective local potential to account for the electronically off-diagonal nonadiabatic mass-dependent corrections. Good agreement is found with previously calculated eigenvalues of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$. The scattering length for the ground state ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$ of ${\mathrm{H}}_2$ is very sensitive to the nonadiabatic corrections, but is in good agreement with that previously calculated using a reduced mass based on the separated atomic masses. Using quantum close-coupling methods, we also find good agreement with previously calculated collision-rate coefficients in the T→0 limit for collisions of H with H and D with D.

Various secondary ions have been produced under 1.5-MeV/amu ${\mathrm{Ar}}^{13+}$-ion impact on a condensed CO target. Multiply charged ${\mathrm{C}}^{\mathit{i}+}$ and ${\mathrm{O}}^{\mathit{i}+}$ ions including H- and He-like ions have been observed to be unexpectedly large compared with condensed rare-gas targets and understood to be due to large initial kinetic energies, which are gained through Coulomb explosion of multiply charged molecular ions produced inside condensed targets during energetic collisions. The prominent positive cluster ions are [CO(CO${)}_{\mathit{n}}$${]}^{+}$ as expected, whereas the negative cluster ions are [${\mathrm{C}}_{\mathit{n}}$${]}^{\mathrm{-}}$.

We present measured triply differential cross sections for the ejection of two electrons into the forward direction following impact of 400-, 600-, and 1000-eV electrons on helium atoms. The coplanar, symmetric geometry was used with a scattering angle of 4°. A comparison with our theoretical calculations demonstrates the clear effect of the final-state electron-electron correlation in fast electron-atom ionizing collisions.

We have attempted to measure total cross sections (${\mathit{Q}}_{\mathit{T}}$’s) for positrons and electrons scattered by potassium and rubidium atoms in the energy range 1–102 eV using a beam-transmission technique. The measurements are subject to increasing errors as the projectile energy is reduced below 20 eV due to the incomplete discrimination of our apparatus against projectiles scattered through small angles. Our measured positron-K and -Rb ${\mathit{Q}}_{\mathit{T}}$’s each show a peak in the vicinity of 6 eV and decrease substantially as the positron energy is reduced below 6 eV. The observed peaks may be artifacts due to the incomplete-discrimination problems referred to above, but careful consideration of those problems does not resolve the marked discrepancies between our low-energy positron-Rb results and those obtained in recent five-state close-coupling-approximation calculations.

The width of the argon 2s level was experimentally obtained from x-ray emission-spectroscopy (2.25±0.15 eV) and x-ray photoelectron-spectroscopy (XPS) (2.25±0.05 eV) measurements. A theoretical value of 1.85 eV was obtained by a Green’s-function calculation. A high-energy satellite located 2.7±0.2 eV above the ${\mathit{L}}_{1\mathrm{-}}$${\mathit{M}}_{2,3}$ x-ray emission transition was confirmed and identified as the 2${\mathit{s}}^{\mathrm{-}1}$3${\mathit{p}}^{\mathrm{-}1}$→3${\mathit{p}}^{\mathrm{-}2}$ double-hole transition. The XPS measurement of the argon 2s ionization energy gave a value of 326.25(5) eV.

In the classical limit and within the infinite-order sudden approximation (IOSA), the tetradic collisional spectroscopic cross sections are transformed into a dyadic supermatrix. Each element of this matrix is expressed in terms of generalized state-to-state cross sections, each row or column corresponding to a given spectroscopic branch. These generalized cross sections are convenient both for ab initio calculations, including possible energy corrections to IOSA, and for modeling. One of the main advantages of the present approach is to give a clear understanding of the line-coupling mechanism and of its spectral consequence on complex systems, whatever the type of spectroscopy (infrared absorption, isotropic or anisotropic Raman scattering) and whatever the nature of the observed vibrational transition (stretching or bending band). To illustrate this point, the strong-collision model is used to calculate explicitly the generalized state-to-state cross sections. This model allows one to justify, on a first and simple physical basis, the origin of the ad hoc decoupling ‘‘factor of 2’’ previously introduced to fit the infrared Q-branch profiles for bending bands.

Absolute intensities of various transitions from n=3, 4, 5, 6, and 7 levels in C iv ions have been measured in the recombination phase of a Θ-pinch plasma. The discharge vessel was filled with 1.87 Pa (14 mTorr) of acetylene and 0.07 Pa (0.5 mTorr) of hydrogen gas to generate the plasma. The deduced upper-level populations showed inversions for all levels of n=4 and above. An experiment to produce laser gain at 253.0 nm showed only a factor of 6 enhancement in the line intensity, i.e., there was no lasing. The lack of lasing was attributed to the small gain coefficient, to losses in the cavity, and to the reduced transmission of light at the vacuum-interface quartz windows (due to a coating from the plasma).

Using three-step laser excitation in an atomic beam and a time-resolved spectroscopy technique, we measured both the lifetimes of the Rydberg levels of Yb i belonging to the perturbed series 6nsp ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_2$ and the lifetimes of the perturbing 4${\mathit{f}}^{13}$5${\mathit{d}}^2$6s ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_2$${,}^1$${\mathit{D}}_2$ levels. An expected shortening has been observed for the lifetimes of those levels which are strongly mixed with the perturbers.

The eigenstates of linear combinations of the Susskind and Glogower phase operators [Physics 1, 49 (1964)] for the harmonic oscillator are constructed. It is shown that such eigenstates are squeezed states.

The effects of the dipole-dipole interaction on atomic dynamics in M-photon processes are studied. The general expression for atomic inversion in an arbitrary initial field state is presented. We find that, generally, there are three series of collapse revivals. If the dipole-dipole interaction can be neglected, there will be two series of collapse revivals. If the field is strong enough, there will be only one series of collapse revival; this is similar to the one-atom case.

We performed state-of-the-art calculations of the emitted-electron kinetic-energy distribution for atomic hydrogen, initially in its ground state, and interacting with a linearly polarized laser field. The laser had frequencies in the one-photon-resonant (1s+ω→2p), two-photon-ionization regime, and irradiances between ${10}^{13}$ and ${10}^{14}$ W/${\mathrm{cm}}^2$. A direct numerical solution of the time-dependent Schrödinger equation was performed using a standard method, and incorporating ‘‘slow’’ laser turn-on and turn-off pulse envelope switching functions. Structure was observed, in addition to the usual above-threshold-ionization peaks. This was deduced to be an effect of the Rabi coupling between the 1s and 2p states. The precise form of this structure was found to depend on both the laser detuning and the irradiance, but was unaffected by the turn-on transient.

We analyze and discuss the exact solution of a popular model for the influence of pump statistics on laser and maser fields. This model has attracted some attention in recent years and has been used to describe noise reduction in lasers, masers, and micromasers. We show that this model has some serious problems and can create negative probabilities in the photon-number distribution. We determine the origin of the model’s deficiency.

We analyze the excitation of atoms by intense pulsed laser fields and describe a mechanism leading to effective dynamical stabilization at a photon energy below the unperturbed binding energy. At low and intermediate intensities, the atom is left in a coherent superposition of the initial state and a set of Rydberg states which is stable against ionization; this effect subsists for pulse durations presently accessible to experiment. At higher intensities, population is transferred through degenerate Raman coupling to Rydberg states of higher angular momentum.

The effect of plasma dispersion in longitudinally pumped x-ray lasers prepared by optical-field-induced ionization is investigated. Dispersion is shown to bound the x-ray peak intensity along the laser and to stretch the pulse in time, thus coincidentally giving a saturated output energy fluence that increases linearly with laser length as in the nondispersive regime. High output efficiencies η>${10}^{\mathrm{-}4}$ in Li-like Ne at 98 Å are thus accessible in x-ray lasing plasmas of high density ${\mathit{n}}_{\mathit{e}}$>5×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$, low temperature ${\mathit{T}}_{\mathit{e}}$<40 eV, and large radius a>20 μm, despite significant dispersion.

The predictions of the Vogel-Schleich (VS) phase theory are compared to the recent experimental quantum phase measurements of Noh, Fougères, and Mandel (NFM) [Phys. Rev. Lett. 67, 1426 (1991)]. Agreement is found to be excellent over the expected range of validity of the VS theory. Hence it appears that, contrary to the view of NFM, an abstract phase theory can predict their results independently of the detailed experimental configuration.

A noninversion laser system which is closed lifetime broadened and free of the restriction on atomic decay rates is proposed. For the realization of lasing without inversion, the Rabi frequency of the applied field must exceed a lower threshold. Moreover, the coherence term in dressed states must enhance the gain. These results are obtained beyond the specific approximations.

An analytical description of the soliton self-frequency shift (SSFS) of dark solitons is presented, using the conservation laws of the nonlinear Schrödinger equation. It is shown that the influence of intrapulse Raman scattering on dark solitons crucially depends on the sign of soliton’s velocity. Our analytical expressions qualitatively explain the main features of the SSFS of the dark solitons observed recently both in experiment [A. M. Weiner, R. N. Thurston, W. J. Tomlinson, J. P. Heritage, D. E. Leaird, E. M. Kirschner, and R. J. Hawkins, Opt. Lett. 14, 868 (1989)] and in numerical simulation [A. M. Weiner, R. N. Thurston, W. J. Tomlinson, J. P. Heritage, D. E. Leaird, E. M. Kirschner, and R. J. Hawkins, Opt. Lett. 14, 868 (1989); Yu. S. Kivshar and V. V. Afanasjev, ibid. 16, 285 (1991)].

A search is conducted for physical quantum-mechanical supersymmetries involving the hydrogen atom. In all coordinate systems admitting a direct separation of the Schrödinger equation, the structure of the separated equations is examined for possible supersymmetric extensions. In addition to the known supersymmetry involving the radial equation for spherical coordinates, we uncover a related supersymmetry involving the radial equation for conical coordinates and a pair of supersymmetries involving parabolic coordinates. The associated spectra and possible physical import of the latter are discussed. They connect certain eigenfunctions of the hydrogen and lithium atoms in the unbroken-symmetry limit. Following the established procedure for the case of spherical coordinates, the breaking of these parabolic supersymmetries is incorporated in a model constructed using notions of quantum-defect theory. The model yields analytical wave functions in parabolic coordinates for the valence electron of alkali-metal atoms, while correctly reproducing the eigenvalue spectra. These ideas are applied to the study of the Stark effect in alkali-metal atoms. Using supersymmetry-based quantum-defect eigenfunctions, we obtain Stark maps for lithium and sodium. The spherical case shows striking agreement with experiment.