We show how the multiphoton-ionization matrix element for an atom in a laser field at intensities beyond the regime of perturbation theory can be calculated from the standard Floquet expansion of the electron wave function. We expand the harmonic components in a discrete complex Sturmian basis set, and we evaluate the resulting (divergent) sum for the matrix element by using the Padé method. We present results for partial rates and angular distributions for hydrogen.

The influence of the microscopic shape anisotropy of the micelles on the pitch of a cholesteric lyotropic liquid crystal is investigated by x-ray diffraction and optical techniques. The mixture studied is potassium laurate, decanol, water, and brucine sulfate. The relative molar concentration of the brucine sulfate is kept constant and the relative molar concentrations of the alcohol and the soap vary. The microscopic shape anisotropy of the micelles is controlled by the balance between the molar concentrations of alcohol and soap. For a fixed molar concentration of the chiral molecule, the greater the shape anisotropy of the micelles, the smaller the cholesteric pitch. This result is discussed in terms of the analogy between the local rotation induced by the chiral molecule and the electrostatic field in a dielectric medium. The relation between the optical birefringence and the shape anisotropy is also discussed.

Exact deterministic equations for the evolution of temporal sequences with a delay stabilization and heat-bath dynamics are derived. The temperature may be arbitrary and both parallel and sequential updating are allowed. The equations display limit-cycle oscillations with a broad diversity of waveforms. For exponential delay it is shown how an increase of the transition amplitude leads to local chaos.

Autoionization of the triplet Rydberg states in the region between the v=0 and v=1 thresholds of ${\mathrm{N}}_2^{+}$ ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$ is observed following photoexcitation from the v=1 level of the E ${}_{}{}^3{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ state of ${\mathrm{N}}_2$. The triplet equivalent of Worley and Jenkin’s np series is observed up to n values of 80. Most of the photoionization intensity in the threshold region derives from autoionization of interlopers of low-n Rydberg states which derive from excited ionic cores $A^2$${\Pi }_u$ and B ${}_{}{}^2{}_{}{}^{}\Sigma _u^{+}{}_{}{}^{}$. Band simulations of the np series and a proposed assignment for the interlopers are presented. Photoionization from other metastable species of ${\mathrm{N}}_2$ is observed as well.

Calculations of the photoelectron angular distribution resulting from N 3p photoionization are compared with experiments at a single energy and reasonably good agreement is found. The energy dependence of the angular distribution and the cross section are discussed.

The photoionization cross section for the excited Na 4d state has been calculated with the multiconfiguration Hartree-Fock method. Ab initio methods are used to take into account the core-polarization effects. The minimum (zero) in the 4d→kp cross section has been calculated and it is found that including the effects of core-polarization shifts the position of the minimum (zero) to a higher energy. The calculation of the photoionization angular distribution asymmetry parameter is an excellent test to locate the minimum (zero) in the cross section. The present results are in good agreement with the experimental results of Smith et al. [Phys. Rev. A 22, 577 (1980)] performed at a single photon energy.

The microscopic system best suited to the high-precision confirmation of a retardation (or Casimir) effect—originating in the finiteness of the speed of light—would seem to be the Rydberg helium atom (a helium atom with one electron in its ground state and the other in a high-n state, preferably with l≊n). For the helium atom, calculation of the retardation energy shift Δ$E_{\mathrm{ret}(\mathrm{n}}$,l) that arises from the retardation effective potential $V_{\mathrm{ret}(\mathrm{r}}$) seen by the outer electron, where r is the separation of the nucleus and the outer electron, is not limited to the case of a Rydberg outer electron. We evaluate Δ$E_{\mathrm{ret}(\mathrm{n}}$,l) numerically in the dipole approximation for a range of values of n and l. The dynamic electric dipole polarizability of the ${\mathrm{He}}^{+}$ core is approximated using pseudostates (a finite number of effective excitation energies and oscillator strengths for the core). We also show how the evaluation can be performed analytically, again using pseudostates. Finally, we give $V_{\mathrm{ret}(\mathrm{r}}$) as an expansion in powers of 1/r; this often provides an easy means of estimating Δ$E_{\mathrm{ret}(\mathrm{n}}$,l) quickly and relatively accurately, and we present various results of use for the Rydberg helium atom, in tabular and graphical form. The effects of exchange, higher multipoles, and of the finite nuclear mass have not been included. As experimental capabilities improve, other systems, such as an ion composed of a nucleus with Z>2, a single core electron, and a Rydberg electron, may someday prove as useful as helium. The formalism for helium can readily be adapted to this case.

Rydberg states of ${\mathrm{H}}_2$ consisting of a 10F or 10G electron bound to the ν=0,R=1 state of ${\mathrm{H}}_2^{+}$ are studied using Doppler-tuned laser spectroscopy of Rydberg-Rydberg transitions. The positions of all such states are measured to a precision of better than 0.01 ${\mathrm{cm}}^{\mathrm{-}1}$ and are compared with the predictions of the polarization model. The polarization model is derived from first principles. Nonadiabatic corrections to the dipole polarization energies, calculated for the first time, are found to be expressible in terms of the $S_{\mathrm{-}3}$-moment functions of ${\mathrm{H}}_2^{+}$. Higher-order adiabatic polarization energies are estimated from calculated higher-order ${\mathrm{H}}_2^{+}$ polarizabilities.

Multiphoton ionization of hydrogen, at laser frequencies, is studied numerically using the stretched hydrogen atom Hamiltonian. In particular, the role of excited bound states in short-pulse, above-threshold ionization (ATI) is emphasized. These states are shown to play a dynamical role both in the production of the higher ATI peaks as well as in the appearance of peak substructure. A simple criterion is used to assess the importance of this process, as a function of field strength and frequency. Arguments are presented for the interpretation of ionization characteristics for short pulses which suggest important differences from that for longer pulses. The extension of these ideas to other frequency regimes is also discussed.

We employ crossed-beam laser spectroscopy with a frequency-stabilized laser diode to measure the Stark shift of the 6$P_{3/2}$ state relative to the ground state of atomic cesium. The scalar and tensor polarizabilities are determined from the measured Stark shifts in the transitions 6$S_{1/2}$ F=4→6$P_{3/2}$ F’=5, $M_F$=5 and 4. Our results are ${\mathrm{\alpha }}_0$(6${\mathit{P}}_{3/2}$)+${\mathrm{\alpha }}_2$(6${\mathit{P}}_{3/2}$)-${\mathrm{\alpha }}_0$(6${\mathit{S}}_{1/2}$)= 977.8(19)${\mathit{a}}_0^3$ and ${\mathrm{\alpha }}_2$(6${\mathit{P}}_{3/2}$)=-262.4(15)${\mathit{a}}_0^3$.

The spectrum of Kr vi has been observed in the 450–1000-Å wavelength range, and 15 lines have been identified as transitions between levels of the 4$s^2$4p, 4s4$p^2$, 4$s^2$4d, and 4$s^2$5p configurations. For seven of the lines the classification is new. All but three of the 14 levels that belong to the configurations have been determined. The result of this analysis is supported by isoelectronic comparisons along the Ga isoelectronic sequence. The configurations are interpreted by fitting the theoretical energy parameters to the observed levels with use of least-squares techniques.

The dc-field-induced interference effects in recombination in a model system consisting of two close-lying autoionizing states are studied. The two states are strongly coupled by a dc field and can decay via both autoionization and spontaneous emission. All possible channels of radiative decay are included for the model system. In special cases the isomorphism of the recombination and photoionization studies is established. The total integrated recombination probability is calculated and its behavior as a function of dc field is presented. Our density-matrix calculations lead to the known results in the limiting case of no dc field.

A quantum nondemolition (QND) measurement scheme utilizing a Kerr medium enclosed in a resonant cavity is described and analyzed theoretically. The theory demonstrates that the conditions for QND can be met in such a device. An experimental realization in the form of an optical-fiber ring resonator has been constructed and initial experimental results are presented.

For the nonrelativistic Kepler problem it is well known that there exists a transcendental equation (the so-called Kepler’s equation) which gives a position in the orbit at a given time. The precessing orbit of the relativistic Kepler problem is reduced to the nonprecessing one by using the transformation related to a rotating Laplace-Runge-Lenz vector. This vector is an extension of the familiar conserved vector and is always oriented to the moving perihelion point of the precessing orbit. From the considerations on Kepler’s equation and the rotating Laplace-Runge-Lenz vector, a relativistic Kepler’s equation is newly defined to find a position in the precessing orbit at a given time. This equation has two expressions corresponding to the relativistic coordinate time and proper time. By using the equation, Lambert’s theorem that gives the required time on the orbit is extended to the relativistic problem.

We formulate radial coherent states for the isotropic harmonic oscillator from the unitary irreducible representations associated with the radial spectrum-generating group Sp(2) which is locally isomorphic to SU(1,1) and SO(2,1). We further consider the time evolution of a coherent-state wave packet and show that, in contrast to the ordinary oscillator coherent states, this wave packet does change its shape (periodically) as it evolves. This change of shape may be interpreted in terms of a generalized squeezing.

A time-dependent, axisymmetric code is employed to examine the development of sidebands in a free-electron laser. For the case where the input signal undergoes an extended period of exponential growth, a broad spectrum of sidebands with growth rates comparable to that of the signal is excited. In general, in an untapered system the optical field displays considerable modulation after several synchrotron periods. An analytical model, in qualitative agreement with a number of features of the simulations, is discussed. In a tapered system the amplitude of the sidebands approaches a quasisteady level that is several orders of magnitude below that of the untapered case, and the output optical field displays only a slight modulation. The optimal rate of tapering employed, to maximize efficiency, leads to substantial reduction in the growth rate of sidebands. This result is discussed in connection with the nonadiabatic nature of particle motion in the tapered system.

The quantum analysis of the influence of a beam splitter on photodetection statistics is discussed. The link between second-order correlation functions and various experimental quantities obtained in photon counting and spectrum analysis is clarified. The introduction of a ‘‘vacuum field’’ is interpreted as a mathematical transformation between two sets of creation-annihilation operators, which can be used as a mathematical device for simplifying the calculations. However, its physical interpretation as a real field is shown to be potentially confusing. The present theoretical approach is used in the interpretation and the analysis of heterodyning experiments of a squeezed signal with a much stronger local oscillator in a coherent state.

We consider the quantization of slowly varying optical fields in a dispersive nonlinear medium and the application of phase-space methods to the resulting quantum field equations. A pragmatic approach to the quantization of the electromagnetic field is adopted whereby we apply canonical quantization to the Hamiltonian expressed in terms of the slowly varying electric field envelope, all approximations (quasimonochromatic and paraxial) having been made at the classical level. This approach allows us to include material dispersion, diffraction, and nonlinearity. Using phase-space methods we then develop a c-number functional Fokker-Planck equation from which the quantum statistical properties of propagating optical fields can be deduced.

Raman-induced phase conjugation (RIPC), a form of four-wave mixing, is used to measure the ratio of the resonant to the nonresonant components of the third-order nonlinear susceptibilities of some derivatives of benzene. This is done by using the dependence of the RIPC spectral shapes on these parameters. A computer code that models RIPC spectra is used to fit theoretical spectra to those obtained in experiment.

A simple N-electron free-electron-laser (FEL) Hamiltonian is seen to define a (1+1)-dimensional quantum field theory. For large N, the FEL dynamics is shown to be solved by a single-electron Schrödinger equation in a self-consistent field. The fluctuations around such a Schrödinger wave function are shown to be O(1/ √N ) and computable by a perturbative strategy. A number of observations are also reported on the best strategy to solve the Schrödinger equation.