The multiple-scattering series for the transition amplitude in gas-surface collisions is examined using elastic atom-surface diffraction as a test bed. Performing numerical calculations for various scattering angles and incident energies, we assess the role of double and triple successive collisions between the projectile and the surface atoms. For rigid lattices, double- and triple-collision terms are found to be significant in the thermal energy regime and even in the higher-energy regime if the surface is highly corrugated. However, at superthermal incident energies (E≳0.2 eV), the single-collision terms give a good approximation to the overall scattering intensities, provided that the ranges of the atom-pair potentials do not overlap; nevertheless, multiple collisions are still important in elastic scattering with large parallel momentum transfers. These results indicate that single-collision approximations should be employed with care for elastic diffraction.

The proportions of keV ions, incident on a clean silicon surface, which are scattered as doubly or triply charged ions are found to increase with atomic number from ${\mathrm{C}}^{+}$ to ${\mathrm{Ne}}^{+}$. In contrast, the recoil ${\mathrm{Si}}^{2+}$ and ${\mathrm{Si}}^{3+}$ ion yields decrease. A definite collision-energy threshold for the production of each of these multicharged ions is found. All the multicharged recoil silicon ion thresholds are consistent with inner-shell vacancy production at the 3dσ-3pπ level crossing. However, the multicharged scattered ions seem to be produced by a different process. The surface-scattered ion yields may follow the same systematics as x-ray yields, which pass through maxima when the shell energies match.

The renormalization of the motion of the valence electrons in metal clusters arising from the coupling to the fluctuations of the cluster surface is calculated. Sizable effects are found, which lead to renormalization coefficients which deviate 30–40 % from unity.

A method of slowing and cooling a thermal sodium atomic beam using the Stark effect to hold the atoms in resonance during the slowing is described. A deceleration of the atoms down to 17 m/s could be experimentally achieved.

Volkov wave functions describe the motion of an electron in a plane-wave laser field and are widely used in the treatment of multiphoton ionization and laser-assisted scattering. These functions are not applicable for fields of a more general type in which the various modes propagate in different directions. Recent work on the development of generalized Volkov solutions, applicable when the field is not a plane wave, is extended here to account for the effect of virtual Compton scattering involving photon pairs that transfer only a small amount of momentum. When such processes occur as initial- or final-state interactions in which the energy of the electron is nearly conserved, near degeneracies are introduced requiring special care in the solution of the wave equation. Methods for constructing approximate solutions that treat these effects accurately are described here for both nonrelativistic and relativistic wave equations. The solutions are used in an analysis of the Kapitza-Dirac effect—the scattering of an electron in a standing-wave laser field—and more general results are obtained than have been in earlier treatments of this problem. In a different class of applications, the generalized Volkov solutions are adopted in a study of the (relativistic) potential scattering of an electron in the presence of a two-mode laser field. A variational formulation, evaluated in the weak-field limit, is used to generate a low-frequency approximation for two-photon bremsstrahlung. A sum rule is derived that provides a simple relation between the true cross section and that obtained with the omission of virtual Compton scattering effects.

We develop a systematic expansion based on a semiclassical description of the ionized electrons for an atom subjected to a laser field. This expansion yields a transition amplitude for atomic multiphoton ionization which accommodates both the above-threshold ionization peaks and atomic resonances. The lowest-order term in the expansion yields the usual Keldysh approximation if the final state is replaced by a plane wave. We show that, even though this term is not reliable in general, it may produce an excellent agreement with the exact result for a three-dimensional zero-range potential and a circularly polarized field. For this situation, we calculate exactly the next nonvanishing term in the expansion, and establish precisely the conditions under which it can be neglected.

We have investigated the change in the transverse-velocity distribution of a beam of metastable argon atoms when crossed by an intense, near-resonant, standing-wave laser field. A time-of-flight technique that provides a better resolution at low velocity than the Doppler fluorescence technique used in earlier experiments has been utilized. The effect of 3–13-photon velocity-tuned (doppleron) resonances in the mean force acting on the atoms has been studied for various laser-frequency detunings and truncations of a Gaussian light beam. The experimental results have been compared with semiclassical laser cooling theory.

The dynamic and steady-state processes of the reverse saturable absorption (RSA) and the related optical limiting (OL) and optical bistability (OB) in metallophthalocyanine have been studied in detail using rate equations and the light-propagation equation. The experiments for demonstrating RSA, OL, and OB in a copper phthalocyanine (CuPc) solution with a Q-switched, frequency-doubled neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser were accomplished. The experimental results were consistent with the dynamic theoretical simulations, also approximately in accordance with the expression of RSA derived from the same equations at the steady-state condition.

A barium atomic beam undergoes selective isotopic excitation by a dye laser to the ${}_{}{}^1{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$ state. This state radiatively decays back to the ground state or to the (6s5d)D states, which are deflected out of the beam by an inhomogeneous magnetic field. The residual atomic beam is examined by a quadrupole mass spectrometer, and isotopic depletions of up to 60% are obtained using laser powers of a few hundred milliwatts. The isotopic splitting of the ${}_{}{}^1{}_{}{}^{}$${\mathit{S}}_0$${\to }^1$${\mathit{P}}_1$ transitions for ${}_{}{}^{136}{}_{}{}^{}\mathrm{Ba}$ and the F=5/2 states of ${}_{}{}^{135,137}{}_{}{}^{}\mathrm{Ba}$ are measured relative to that for ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$ and agree well with those found previously.

We discuss atomic stabilization in the process of resonance ionization via Rydberg states. We show that a strong resonance interaction between Rydberg states and a low-lying state substantially suppresses ionization. As a result, the population is trapped in the Rydberg states. Raman-type coupling of Rydberg states via the continuum is shown to be essential for the effect even when the bound-free interaction is weak.

We study the ionization of atoms in weak, strong, and ultrastrong laser fields and especially the possibility to approximate the sinusoidal electric field of the light by alternating δ kicks of appropriate strength. The dynamics of a one-dimensional model atom is considered as well as the real three-dimensional hydrogen atom. We found that the qualitative behavior of the ionization probability and the photoelectron spectrum is not changed by the above-mentioned approximation. However, the effect of the so-called stabilization in ultrastrong fields (fields far beyond the perturbation theory) is stronger with the kick approximation than for a realistic field. This can be understood within the framework of the Kramers-Henneberger picture.

The purpose of this paper is a theoretical study of forces induced by a laser beam on nonresonant cold atoms in the vicinity of a metallic surface. We use the same quantum electrodynamics formalism to study and compare all the kinds of forces which can occur. In a first step, when no incident light is present, forces are caused by exchanges of virtual photons and we recover the monoatomic Casimir force and the interatomic van der Waals force, modified by surfaces effects. In a second step, a laser beam is present and we calculate the induced gradient force on one atom and the interatomic light-induced force, which is a binding when similar atoms are considered. Laser light creates interference fringes above the metallic surface which induces an energy grating, where individual atoms could be trapped. Then we study the optical binding for various atoms positions in the fringes. We compare these forces near a perfect metallic surface and the same forces in free space.

Photodissociation spectra of ${\mathrm{H}}_2^{+}$, obtained using ultrashort (a few femtoseconds), intense (within the range of ${10}^{12}$ to ${10}^{14}$ W/${\mathrm{cm}}^2$) laser pulses (with a peak frequency of 3.761 eV), and displaying well-separated proton kinetic-energy peaks corresponding to one-, two-, or three-photon absorptions are analyzed. Within some approximations, the validity range of which is related to the aforementioned assumptions on the laser and spectrum characteristics, a simple analytic formula is deduced. It gives the spectral widths of the observed peaks in terms of the total number of photons which are absorbed and/or emitted during the dissociation process. A quantitative support to some recent dynamical interpretations is provided. The successive absorption of three photons seems basically to be the initial step which, at intermediate intensities, leads to the three-photon peaks. A subsequent emission of one (or two) photons is responsible for the two- (or one-) photon peaks. Bond softening occurs at higher intensities by the lowering of potential-energy barriers. Dissociation proceeds through these barriers by reflection and tunneling. It involves at least three photons to end in a one-photon peak.

We discuss behavior of a two-electron classical system in a very intense laser pulse of high frequency. We demonstrate significant two-electron stabilization with electrons localized on the opposite sides of the nucleus.

Within certain limits, the dynamics of a single trapped ion oscillating about the node of a standing-wave light field is described by the Jaynes-Cummings model, which is routinely used for cavity-QED experiments. We propose a technique to measure quantum collapse and revival in the population inversion of a single trapped ion, and show that this method is uniquely suited for the measurement of final temperatures of the trapped ion as well as for the analysis of nonclassical states of the ion motion, such as Fock and squeezed states. The results are discussed with particular consideration given to the effects of a finite laser bandwidth.

We present results of calculations of perturbative rates for two- and three-photon detachment and ionization of ${\mathrm{H}}^{\mathrm{-}}$ and He, and for simultaneous excitation of ${\mathrm{H}}^{\mathrm{-}}$, by linearly polarized light over a range of frequencies extending into the ‘‘excess-photon detachment and ionization’’ region, a region replete with resonances. Simultaneous excitation of H is more probable than not in the case of two-photon detachment of ${\mathrm{H}}^{\mathrm{-}}$.

We present a quantum theory of the micromaser which allows for arbitrary (sub- as well as super-Poissonian) fluctuations of the pumping beam. It handles the interaction with the active atoms (gain) and cavity decay (loss) on an equal footing. In conventional reservoir theory the rate of change of the cavity field is a sum of the changes due to separate interactions with the individual reservoirs, i.e., the interactions are uncorrelated. In our approach, corrections to reservoir theory arise. They contain the commutator of the gain and loss operators. The magnitude of these additional terms is characterized by the quantity p/${\mathit{N}}_{\mathrm{ex}}$ where p is a parameter describing pump-beam fluctuations. The parameter is, in fact, the negative of the Mandel Q parameter of the pump beam so that p=1 corresponds to regular pumping, p=0 to Poissonian one and p<0 to super-Poissonian pump beam fluctuations. ${\mathit{N}}_{\mathrm{ex}}$ is the number of excited atoms passing through the cavity during the lifetime of the intracavity field. Thus we recover the conventional reservoir limit if p=0 and/or ${\mathit{N}}_{\mathrm{ex}}$ is large. In all other cases the interactions with the gain and loss reservoirs are correlated. We exploit some of the consequences of the additional terms, presenting analytical as well as numerical results for the steady-state photon statistics (mean photon number and photon-number fluctuations, in particular) without resorting to the p expansion.

A comprehensive formalism for a two-mode SU(1,1) interferometer (a nondegenerate parametric amplifier, a degenerate four-wave mixer, or a phase-conjugating mirror) is presented. The device changes the quantum state of the two incident modes by an SU(1,1) transformation. Apart from phase shiftings, the quadrature wave functions are Lorentz transformed. A transformation formula in the Fock space of the two modes is derived. Hybrids of s and -s quasiprobability distributions are changed by the inverse-mode transformation. It is related to quantum noise in phase conjugation. Linear amplification caused by Gaussian reservoirs corresponds exactly to a heuristic nondegenerate-parametric-amplifier model. It allows a simple geometrical explanation for the sensitivity of squeezing or quantum superposition with respect to phase-sensitive amplification.

The emission of a resonant nondegenerate cascade laser in which up to two fields can be simultaneously amplified inside a cavity is theoretically investigated. Each field is resonantly coupled with one of the transitions of a ladder three-level atomic system, in conditions of homogeneous broadening. General analytical expressions for zero-, one-, and two-field solutions are given. Cooperative emission between both fields is found. Through the linear stability analysis of these solutions we obtain phase diagrams showing their respective domains of stability. Together with the existence of Hopf bifurcations associated with one-photon processes, which coincide with those of a Lorenz-Haken laser, a genuine Hopf bifurcation due to two-photon processes has been found. This last bifurcation does not require the ‘‘bad cavity’’ nor the ‘‘Lorenz threshold’’ conditions. The stability of the orbits that bifurcate from these critical points is analytically investigated. For this we have rewritten one of the standard criteria in a useful and straightforward way. Finally, the dynamic regimes exhibited by the system well above the instability thresholds is numerically investigated revealing transitions to chaos via quasiperiodicity.

We propose a method, which we call the coherent-coupling approach, to determine a slow spontaneous decay rate by coupling coherently a weak atomic transition to a strong one. This approach allows the indirect measurement of a small decay rate from the fast Fourier transform of the time-dependent intensity oscillations of the strong transition, and can be viewed as an alternative to the method of quantum jumps.