We present an improved method for the calculation of positronium-formation cross section from one-electron atomic targets of arbitrary charge $Z_T$. The calculation is complete through second order in the collisional potentials. We use this technique to calculate the positronium-formation cross sections for 1s-1s electron capture from atomic hydrogen.

From new measurements of energy-loss distributions of proton beams in thin solid foils we determine the second- and third-order moments of the energy spectra, and evaluate the skewness coefficient γ, which is of interest in studying the asymmetry of the energy-loss spectra. We present calculations of γ based on electron gas and Thomas-Fermi models; we compare these calculations with the experimental results and with the values derived from Bohr’s energy-loss treatment. We present a theoretical analysis of the effects of surface roughness on the skewness of the energy-loss distributions.

In this paper the optical pumping of a cesium beam is investigated. The rate equation model is used to calculate the population difference created by laser diode(s) illuminating the beam. The finite laser and atomic linewidths are taken into account in order to analyze leakage effects on neighboring transitions. One-laser and two-laser pumping is considered and the best-suited two-laser configurations for preparing the cesium atoms in a single $m_F$=0 sublevel are specified. Experimental results on both the leakage effect and the population difference achieved agree with theoretical predictions.

New measurements of the rototranslational collision-induced absorption spectra in the far-infrared (FIR) frequency region of gaseous mixtures of hydrogen (${\mathrm{H}}_2$) and helium (He) are reported. The frequency range extends up to 1500 ${\mathrm{cm}}^{\mathrm{-}1}$ at the temperature of 195 K, and 1700 ${\mathrm{cm}}^{\mathrm{-}1}$ at 296 K. The uncertainties of the measurement are assessed. Comparison with previous measurements show substantial agreement at frequencies where the measurements overlap. For comparison with the measurement, spectra are computed from the fundamental theory using a state of the art ab initio dipole function and an isotropic potential surface as input. The observed agreement suggests that for important applications, such as the analysis of the FIR spectra of the outer planets, the spectra can be obtained reliably as a function of frequency and temperature from quantum calculations of the kind presented here.

Torsional-rotational levels of methanol with energies between 127 and 1600 ${\mathrm{cm}}^{\mathrm{-}1}$ are considered. A description of the procedure for the assignment of the levels is given. A comprehensive statistical study of these levels is made utilizing the nearest-neighbor level-spacing distribution, correlation coefficient, ${\Delta }_3$ statistics, and Q statistics. The results of this analysis are discussed. This work, which treats 2396 levels, completes an earlier work, which reported an analysis involving 1340 levels [Phys. Rev. A 32, 3797 (1985)].

The irreducible moment version of the recursive-residue-generation method is used to study the dynamical behavior of a multimode system, where one radiatively active mode is coupled to a laser field and in turn, intramolecularly, to a set of inactive background modes. Nonperiodic behavior of the survival probability ‘‘observable’’ is numerically detected under certain conditions (large enough background and a randomly scattered frequency spectrum). A quantitative condition is given for the prevalence of this seemingly ‘‘chaotic’’ dynamics.

A comprehensive experimental study of the energy and angular distributions of electrons ejected from the Sr 5$p_{3/2}$${\mathrm{ns}}_{1/2}$ and 5$p_{1/2}$${\mathrm{ns}}_{1/2}$ J=1 autoionizing states with n ranging from 10 to 20 has been performed using multistep laser excitation and time-of-flight electron spectroscopy. The branching ratios for autoionization to the available ${\mathrm{Sr}}^{+}$ ion cores have been determined as well as the asymmetry parameter, β, of the electron angular distributions. Both the branching ratios and the β parameters are constant across isolated autoionizing states. However, measured β values and branching ratios change sharply across the line profiles of those 5$p_{3/2}$${\mathrm{ns}}_{1/2}$ states which have strong localized interactions with 5$p_{1/2}$${\mathrm{ns}}_{1/2}$ and 5$p_{1/2}$${\mathrm{nd}}_{3/2}$ states. A consistent six-channel quantum-defect-theory model has been developed which enables us to reproduce quite well the level positions, the total autoionization rates, the branching ratios to different ${\mathrm{Sr}}^{+}$ ion states, and the angular distributions of the electrons ejected in the autoionization to the ${\mathrm{Sr}}^{+}$ 5$s_{1/2}$ and 5$p_{1/2}$ ion states.

It is shown that if time delays are not neglected, a pendular Fabry-Perot cavity is no longer stable in some cases of actual interest, including some configurations of each arm of the interferometers designed to detect gravitational radiation.

We present the quantum theory of a microscopic maser operating on a degenerate two-photon transition between levels of the same parity. We derive both a master equation and a Fokker-Planck equation for this system, and show that quantum effects may have a substantial influence on the behavior of the maser. They modify the oscillation threshold and make external triggering of this maser unnecessary, whereas, according to semiclassical theory, such a triggering is required to start up the maser oscillation. We derive the phase-diffusion properties of the field and show that the diffusion coefficient is complex in this case, its imaginary part being associated with a frequency shift of the field inside the cavity. We show that, in steady state, the photon-number statistics is sub-Poissonian for a wide range of pumping rates.

We study laser-induced dissociation of a Morse oscillator by an ir field as a prototype of multiphoton excitation and dissociation of molecular systems. The driving field is modeled both by a sinusoidal interaction term and by a sequence of δ impulses. We have found that the latter case yields results which closely resemble those of the former and considerably facilitates the computation and analysis. Primary and a sequence of secondary resonances are found in our classical dynamical study and are analyzed by using Chirikov’s nonlinear resonance theory. We have also calculated the dissociation rate as a function of time, dissociation fractions, and half-lives, all for ensembles of initial states uniformly distributed over regions in the phase space. The half-life as a function of the driving field amplitude follows a scaling law with a critical exponent in close agreement with that predicted for the standard map. This fact and the time-dependent dissociation rate reflect the effects on dynamic flows of the partial barriers formed by cantori.

Operators are defined which correspond to the real and imaginary parts of the square of the field amplitude. These operators obey an uncertainty relation. Squeezing with respect to these operators is defined and minimum uncertainty states are discussed. A number of nonlinear optical processes are examined and shown to produce this effect. Interactions which couple one mode amplitude to the square of another convert this type of squeezing into normal squeezing. An example of such an interaction is given.

A quantum optical formulation of the action of passive, lossless optical instruments on quantum light fields is developed. The quantum Maxwell equations are formally solved and the commutation relations for various combinations of field operators at different times are studied. General relationships between field correlation functions and correlation functions of source-quantity operators and free-field operators are derived. Formulas are presented for the case when the free field is the vacuum field. Furthermore, the mixing of source-field light with coherent free-field light is treated. The theory is applied to the calculation of the photocount distribution. The theory presented renders it possible to take into account the effects of light propagation through the optical system. It is shown that the effect of the optical instruments may be taken into account by introducing an apparatus function in a way which formally corresponds to that of classical optics. However, the calculation of the corresponding convolution integrals is governed by operator ordering rules, which are essential in the case of quantum light fields and which can give rise to substantial differences between classical and quantum optics.

We evaluate the velocity distributions for both atomic states for optically active two-state atoms immersed in a buffer gas and irradiated with a broadband radiation field. Collisions with buffer-gas particles are assumed to be completely thermalizing and the collision rates are state dependent. Furthermore, we calculate the drift velocity and the anisotropic diffusion tensor as functions of various parameters of the system. In particular we give explicit results for the case of a spectral distribution in the shape of a step function. The results determine the basic equations for light-induced drift and diffusive pulling.

This paper presents a general theoretical analysis of optical-frequency mixing of the radiation of n different laser beams (n=1,2,3,. . . ) in gaseous media with arbitrary density distribution. Phase-matching conditions between the induced nonlinear polarization and the generated optical radiation are calculated for third- and fifth-order sum- and difference-frequency mixing in free expanding gas jets taking into account absorption of the generated light and displacements of the foci of the laser radiation from the center of the gas jet.

A new kind of free-electron-laser (FEL) scheme is proposed, that is, an FEL with an electrostatic centrifugal system of coaxial waveguide, called an ‘‘electrostatic FEL’’ for short. An annular relativistic electron beam in the laboratory frame is assumed to encounter a pump wave of TE mode. Solving the Vlasov-Maxwell equations, we have developed the kinetic theory of the above scheme, and obtained the nonlinear dispersion relation describing the various instabilities of the wave modes which can be supported by the system. We have also numerically solved the dispersion relation in the case of taking both pump wave and scattered wave to be the ${\mathrm{TE}}_{11}$ wave mode, and presented the instability structures, in the beam frame, of Compton scattering (two-wave effect) and Raman scattering (three-wave effect) versus the strength of the pump field. Numerical examples demonstrate that this new FEL scheme is of great interest theoretically and practically.

We analyze the transient probe spectra that arise when two-level atoms in an atomic beam are excited by a ‘‘pump’’ laser field and are probed by a step-function weak field on the same atomic transition. The temporal relaxation of the probe spectra to their steady-state values is found to depend critically on the initial atom–pump-field dressed-state populations and coherences. The transient spectra may be composed of absorption-emission structure that is totally absent in the steady-state limit. A simple physical interpretation of the spectra is given in terms of a conventional dressed-atom picture. In addition, we study the effects of collisions on transient probe spectra and investigate the transient buildup of several collision-induced features in the spectra.

We consider propagation of optical pulses in the anomalous dispersive region of single-mode fibers after including the effects of Kerr-type nonlinearity. It is found that the pulse develops an internal structure with deep amplitude modulation. We show that this self-amplitude-modulation of pulses is related to the modulation instability of continuous-wave optical beams in nonlinear dispersive fibers. The initiation of this phenomenon does not require an external probe or spontaneous emission. Numerical results show that self-phase-modulation broadens the power spectrum enough to encompass the frequency at which self-amplitude-modulation provides the maximum gain. The amplification of these sidebands manifests as a breaking of the optical pulse into several subpulses. For negligible loss, the pulse breakup may also be viewed as the internal structure of a high-order soliton. However, modulation instability appears to provide a simpler interpretation and explains the features of numerical simulation and experiments.

Gaussian kernels representing operators on the Hilbert space scrH=$L^2$(${\mathrm{openR}}^n$) are studied. Necessary and sufficient conditions on such a kernel in order that the corresponding operator be positive semidefinite, corresponding to a density matrix (cross-spectral density) in quantum mechanics (optics), are derived. The Wigner distribution method is shown to be a convenient framework for characterizing Gaussian kernels and their unitary evolution under Sp(2n,openR) action. The nontrivial role played by a phase term in the kernel is brought out. The entire analysis is presented in a form which is directly applicable to n-dimensional oscillator systems in quantum mechanics and to Gaussian Schell-model partially coherent fields in optics.

Two counterpropagating intense light beams linearly polarized along the fast axis of a birefringent fiber may constitute a spatially unstable polarization eigenarrangement. Chaotic behavior in the steady-state polarization evolution of the waves occurs for input powers in a certain interval of values. By evaluating Lyapunov exponents we show intermittent trapping of irregular trajectories around regular islands. The characteristic length scale of this spatial disorder is typically of the order of one beat length.

Conditions for the design of organic solids capable of optimum nonlinear optical behavior are investigated. Generalized expressions describing optimum phase-matching conditions in crystals of monoclinic symmetry and having one-dimensional hyperpolarizabilities are obtained. The results are applied to specific organic molecular solids. An anisotropic in-plane molecular polarizability is shown to provide the best condition for second-harmonic generation in these systems.