The total cross section for fluorescent scattering by a spherical particle uniformly filled with fluorescent scatters is computed using a model for fluorescent scattering formulated earlier. Results are given for an arbitrary incident beam and for a linearly polarized plane wave normalized to the cross section for the same number of scatterers in bulk medium. The cross section has a form which clearly shows the possibility of resonance peaks when either the incident or the fluorescent frequency (or both) coincides with eigenfrequencies of the particle.

We have measured Lyman-α quantum beats from coherently excited hydrogen atoms produced in 85–235-keV proton collisions with a thin helium jet target. Intensity measurements of the radiation emitted at 90° to the beam direction as a function of distance downstream from the target in electric fields both parallel and antiparallel to the beam axis allow extraction of the coherence between the s and p states by Eck’s method [Phys. Rev. Lett. 31, 270 (1973)]. Because the jet target allows the collisions to occur in the applied field, we have eliminated the problems associated with field inhomogeneities when gas target cells are used. A strong-intensity peak emitted by excited helium in the target allows a determination of the starting point of the evolution in the field as well as a determination of the effects of experimental averaging. We present the s-p coherence parameters as a function of the projectile energy and compare them with recent theoretical calculations.

Differential and integrated cross sections for the formation of antihydrogen by the impact of intermediate-energy (20–500 keV) antiprotons on positronium are calculated using the first Born approximation. The calculations are carried out for the formation of antihydrogen in ground and various excited electronic states (n=1–3) when positronium, the target atom, is in the ground state, and for the formation of antihydrogen in the ground state when the positronium is in various excited electronic states (n=1–2). The 1/$n^3$ behavior for the capture cross sections is used to calculate the total (that is, all states added together) integrated cross sections. The cross sections for the formation of antihydrogen presented here are obtained from those for the formation of positronium by the impact of positrons on hydrogen atoms by using charge invariance and the principle of detailed balance.

Cross sections are presented for the direct electron-impact ionization of the 5p, 5s, and 4d subshells of the ground state of the first six members of the xenon isoelectronic sequence. The calculations were performed in a distorted-wave Born-exchange approximation including the effects of term-dependent partial waves in the ejected-electron channel and ground-state electron correlation. Shape resonances were found to significantly enhance the cross sections at low incident electron energies for Xe, ${\mathrm{Cs}}^{+}$, and ${\mathrm{Ba}}^{2+}$. Term dependence in the 5$p^5$kd and 4$d^9$kf ejected-electron channels was also significant for these ions. Ground-state correlation was somewhat less influential, and affected the cross section only when ejected-electron term dependence was also significant.

We have measured the depolarized-light-scattering spectrum of normal ${\mathrm{H}}_2$ at T=297 K as a function of the density between ρ=17.8 and ρ=129 amagat up to the frequency ν=865 ${\mathrm{cm}}^{\mathrm{-}1}$. The spectrum between 6 and 240 ${\mathrm{cm}}^{\mathrm{-}1}$ is dominated by the ‘‘translational’’ depolarized interaction-induced part from which the two-body spectrum and the three-body correlation spectrum have been extracted and compared with the theoretical predictions obtained with the dipole-induced-dipole polarizability model and an isotropic pair-interaction potential. We have also measured the spectrum in the wings of the rotational transition S(0),S(1),S(2) between 240 and 865 ${\mathrm{cm}}^{\mathrm{-}1}$ and demonstrated, for the first time, its quadratic behavior versus density in the above-mentioned density range. This portion of the spectrum is attributed mostly to pure collisional broadening.

A particular well-defined enveloping construction based on the Hermitian representation of the complex-coordinate method combined with a projection-operator argument leads to a rigorous criterion for the existence of a resonance eigenvalue within a given region in the complex energy plane. The geometrical realization of this idea involves the analysis of a certain ichthyoid ‘‘fishlike’’ enveloping construction. Results for a simple model potential are displayed.

Wavelength measurements of n=3 to n=2 transitions in neonlike ${\mathrm{Xe}}^{44+}$, ${\mathrm{La}}^{47+}$, ${\mathrm{Nd}}^{50+}$, and ${\mathrm{Eu}}^{53+}$ have been made using a high-resolution Bragg-crystal spectrometer on the Princeton Large Torus tokamak. The measurements cover the wavelength regions 2.00–3.00 Å and include the electric dipole and the electric and magnetic quadrupole transitions. The measured wavelengths are compared to energy levels obtained from a multiconfigurational Dirac-Fock calculation. Systematic differences between the experimental and theoretical values are found, which vary smoothly with atomic number. The magnitude of the differences depends on the particular type of transition and ranges from -2.8 eV to +2.2 eV. Inclusion of electron correlation corrections due to ground-state correlations and (super-) Coster-Kronig-type fluctuations in the theoretical energies is shown to reduce the differences for some but not all types of transitions.

The cavity shifts in the cyclotron motion of a charged particle in a hyperbolic Penning trap are described using a numerical evaluation of the cavity-mode structure. The frequency shifts are about half as large in the hyperbolic cavity as in a cylindrical cavity of equivalent size. However, this still implies an error in the g-2 experiment that is easily five times the present statistical uncertainty. To account for slit electrodes and imperfect tolerances in existing traps, experimental measurements of the mode structure are still needed. The resonant frequencies of a microwave cavity can be measured very precisely. We show here that an accuracy of 10% in the measurements of certain coupling constants is sufficient to compute the shifts for the g-2 experiment at the level of one part in ${10}^9$.

The Stark spectra of autoionizing Rydberg states of Xe converging to the second ionization limit 5$p^5$ ${}_{}{}^2{}_{}{}^{}P_{1/2}^{}{}_{}{}^{}$ have been investigated as a function of applied electric field over the range 26–2362 V/cm. Single-photon excitation from the Xe ground state was achieved using coherent radiation near 92.5 nm, generated by frequency tripling the pulsed output of a frequency-doubled dye laser in a free jet of rare-gas atoms. For the lowest electric field only the ns’ and nd’ series were observed. As the electric field was increased the np’ series appeared because of the mixing of wave functions with different l values. Further increase of the electric field caused the appearance of hydrogenlike Stark manifolds. The Stark spectrum was simulated in a two-step procedure with no adjustable parameters. Using a jl-coupling basis set the Hamiltonian matrix was diagonalized to determine the energy levels and corresponding eigenfunctions for a given electric field strength. The intensities and line shapes were then calculated using the formalism developed by Fano for a many-discrete-level–single-continuum configuration interaction. This treatment was sufficient to reproduce the positions, widths, and shapes of most observed features. At field strengths between 1000 and 2000 V/cm, however, an additional modulation structure with a spacing of about 2.7 ${\mathrm{cm}}^{\mathrm{-}1}$ appeared on top of the ‖M‖=1 autoionizing resonances, which could not be explained by our simple theoretical model.

The responses of the time-dependent resonance fluorescence spectra of two-level atoms in the presence of (a) strong cw laser fields and (b) short pulsed laser fields to functional disturbances in these fields have been studied by the use of functional-sensitivity-analysis techniques. For the cw case, the transient and steady-state response regions are explored separately. It is found that the response to the field disturbance occurring during the earlier transient period is most prominent at the positions of the well-known three peaks of the corresponding spectrum. In contrast, the response to a disturbance taking place in or near the steady-state region tends to increase the separation between the peaks and lower the intensity of the line center, in exact agreement with the direct calculation of the perturbed spectrum. For the pulsed case, the response to the disturbance is most visible at the line center and at the accompanying multiple peaks caused by the population oscillation of the upper atomic level. The response strongly depends on the magnitude of the pulse area, thus giving rise to distinct asymptotic behavior for (2n+1)π and 2nπ pulses. As the pulse area becomes large enough to cause significant population oscillation of the upper atomic level, the response of the spectrum shows a resemblance to that of the cw case.

Using a multichannel version of the quantum-optical model of above-threshold ionization, we compute the angular distribution of photoelectrons for atomic hydrogen irradiated by a powerful linearly polarized laser pulse. We take into account the distortion of atomic continua by the presence of the strong laser. The distributions are peaked along the polarization direction. The results are in striking but qualitative agreement with the recent experiment of D. Feldmann et al. [Z. Phys. 6, 293 (1987)] for six- and four-photon ionization of hydrogen.

The branching ratios for radiative decay of H atoms excited in small electric fields (0–5 V/cm) have been calculated for the nl states up to n=6. A simple computational procedure was employed, allowing only for Stark-effect mixing of levels with the same values of the quantum numbers (n,j,$m_j$). The results are compared with more detailed calculations available for 3l-state decay made using the density-matrix formalism, and new calculations of this type reported here for 4l-state decay. In conjunction with theory, this allowed the domain of validity of the simple computational procedure to be established as a function of n. The results show that the branching ratios depend quite strongly on electric-field magnitude, pointing to the need to exercise caution in measurements of H emissions, and in application of the available data to other problems.

We have measured ${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$${:}^9$Be isotope shifts in the ${}_{}{}^1{}_{}{}^{}\mathrm{S}$ and ${}_{}{}^1{}_{}{}^{}\mathrm{D}$ Rydberg series by resonance-ionization mass spectrometry. Pronounced interference of exchange and correlation contributions to the isotope shift is observed in the ${}_{}{}^1{}_{}{}^{}\mathrm{D}$ series, reflecting strong interaction of 2snd and 2pnp channels. The finite-mass correction to the ionization energy of ${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$ is inferred to be 270±40 MHz.

Collinear laser–ion-beam spectroscopy has been used to measure hyperfine structure (hfs) in three levels of the 3$d^2$ and six levels of the 3d4p configuration of Sc ii. The results combine with earlier measurements of hfs within these configurations to give a fairly complete picture of hfs in these configurations. The combined results are compared with multiconfiguration Dirac-Fock (MCDF) ab initio calculations. Good agreement is obtained for the magnetic dipole hfs constants of the singlet states in both the 3$d^2$ and 3d4p configurations, but the MCDF predictions for the triplet states are not even qualitatively correct. The poor agreement for the triplet states appears to be due to the neglect of core polarization in the present MCDF approach.

In this paper we analyze two-photon-resonant three-photon ionization of atomic oxygen via the 2${\mathit{p}}^3$${(}^4$S°)${\mathit{np}}^3$${\mathit{P}}_0$,1,2, and the 2${\mathit{p}}^3$${(}^4$S°)nf ${}_{}{}^3{}_{}{}^{}$${\mathit{F}}_2$,3,4 states. The various atomic parameters required for calculating the resonant enhanced multiphoton ionization (REMPI) probabilities are obtained using quantum-defect theory. The infinite sums over nonresonant states are truncated at a finite number of terms. Our calculated two-photon excitation cross sections agree well with the results of other recent calculations and of experimental measurements. The photoionization cross section is calculated for various electron kinetic energies. The REMPI dynamics is analyzed by solving the density-matrix equations. This framework consistently takes into account the effects of saturation and ac Stark shifts. REMPI probability is seen to be quite sensitive to the initial detuning, the intensity, and the particular resonant state accessed. The photoionization cross sections also imply that due to the rapid falloff of the cross section, two-color REMPI schemes with a lower-frequency ionizing photon would increase the effective REMPI probability.

It is shown that nonclassical photon states can be produced by generating correlated photon pairs, measuring the idler mode, and manipulating the signal mode using feedforward and linear attenuators, amplifiers, or phase modulators. The minimum achievable Fano factor for such schemes is (2/π〈n〉${)}^{1/2}$, where 〈n〉 is the mean output photon number. A nondegenerate parametric oscillator followed by linear manipulators can reach this limit. A nondegenerate parametric amplifier followed by linear phase manipulation can produce phase-squeezed states. The minimum achievable phase noise is a factor 1/2G below that of a coherent state, where G is the amplifier gain. The advantages with these schemes are wavelength tunability, potentially very high squeezing bandwidth, and relative simplicity.

A quantum-electrodynamic (QED) description of the resonant interaction of monochromatic light with the $3^2$${\mathit{S}}_{1/2}$(F’=2)→$3^2$${\mathit{P}}_{3/2}$(F=3,2,1) hyperfine transitions of the sodium $D_2$ line is formulated in terms of the Heisenberg atomic operator. Off-diagonal state coherences and all relaxation terms are included. It is found that the equations for the populations, optical coherences, and certain state coherences form a closed subset of the total system of equations. This subset is small enough to be computed numerically. The results of calculations with this model are compared with three previously developed semiclassical descriptions using the density operator. One of the semiclassical models was developed to describe the interaction of weak light with the atomic transition while another is suitable in the case of high-intensity light. For both π and σ excitation it is shown that the QED calculated values for the time-averaged, excited-level population probability converge to those of each of the semiclassical models in the appropriate limit of light intensity. For homogeneous broadening, results show that the optimum light intensity to obtain the largest fraction of atoms in the $3^2$$P_{3/2}$ level after transversing a 1-mm-diam laser beam is 1.15 mW/${\mathrm{mm}}^2$ for π excitation and 1.43 mW/${\mathrm{mm}}^2$ for σ excitation.

The gyrotron, the free-electron laser, and the wiggler-free free-electron laser are compared. First, the flows in the three systems are examined in their steady state. Then the interaction of the electron beam with free-space electromagnetic waves is studied by using a fluid picture. The growth rate of the instability is found by calculating the nonreal roots of the three different dispersion relations. It is shown that at off-resonance the interactions in the gyrotron and in the wiggler-free free-electron laser are identical. However, at resonance, the instability in the gyrotron disappears, while the growth rate in the wiggler-free free-electron laser is maximal, as in the usual free-electron laser. The maximum growth rate in the wiggler-free free-electron laser scales as some small parameter to the power of (2/5, compared to the same small parameter to the power of (1/2 for the gyrotron, and to the power of (1/3 for the free-electron laser. Thus the wiggler-free free-electron laser, while having some resemblance to each of the two other systems, the gyrotron and the free-electron laser, is clearly different from both. In terms of gain, it has a higher gain than the gyrotron but lower than the free-electron laser.

A free-electron laser, which employs a high-density thick electron beam, of a thickness comparable to the wiggler wavelength, is considered. Full transverse dependence of the wiggler field as well as equilibrium self-fields of the beam are taken into account. We identify a domain in parameter space where the electron beam is wholly resonant and the gain scales as in the one-dimensional theory of the free-electron laser in the Raman regime. A family of electron-density radial profiles is shown to have a low shear in the resonance parameter and thus to exhibit a particularly high gain.

The time evolution of squeezed vacuum states, taken to be SU(1,1) coherent states, interacting with a two-photon medium is examined using numerical methods. The non-photon-conserving medium is modeled by a Hamiltonian which consists of the free-field term, a non-photon-conserving term in the form of a degenerate parametric amplifier, and an anharmonic term which gives rise to optical bistability. This system has previously been shown to produce enhanced squeezing when interacting with ordinary coherent light. In the present work we find that the squeezing property is generally revoked by the anharmonic term and increased by the nonconserving term. The combined effects are not additive, however, and a quantum interference effect is observed in the calculations.