K x-ray intensity ratios in ${\mathrm{Ti}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{-}\mathit{x}}$ and ${\mathrm{Cr}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{-}\mathit{x}}$ alloys have been measured for different compositions x, using 59.54-keV γ-ray fluorescence (γRF) and 4.07-MeV-proton ionization. The intensity ratios were found to be higher than those of pure metal values for Ti in ${\mathrm{Ti}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{-}\mathit{x}}$ alloys for x=0.35 and for Cr in ${\mathrm{Cr}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{-}\mathit{x}}$ alloys for x=0.20. The γRF results are supported by the proton-induced x-ray emission (PIXE) results for all the constituent metals of both the alloys. The results are discussed on the basis of 3d-electron transfer or rearrangement in the individual metals of corresponding alloys.

High-resolution spectroscopy studies of hyperfine structures of stable terms in ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ i, ii, and iii by quantum-beat and rf resonance spectroscopy after grazing-ion–surface scattering are reported on. From the data, the electric quadrupole moment of the ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ nucleus Q=20.0±0.2 mb and the quadrupole coupling constants ${\mathit{eQq}}_{\mathrm{at}}$/h of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ atoms in 2p and 2${\mathit{p}}^2$ configurations have been deduced. Extrapolation yields ${\mathit{eQq}}_{\mathrm{at}}$/h=11.2±0.2 MHz for a single electron in the ground term of the 2${\mathit{p}}^3$ configuration of the neutral atom.

We present the results of R-matrix calculations for the bound-state properties of the atoms in the carbon group for states with odd parity and J=0–3. The calculations were performed in LS coupling with the fine-structure interaction incorporated through an LS-jj frame transformation. We also present the photoionization cross section of the ${\mathit{ns}}^2$${\mathit{np}}^2$ ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_0$ ground state for each of the atoms for final-state energies between the two ${\mathit{ns}}^2$np ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{\mathit{J}\mathit{c}}^{\mathit{o}}$ spin-orbit split thresholds. We discuss some of the limitations of our method.

We present an energy-spectra study of the hydride diatomic molecules where the parameters are constrained by atomic calculations. By means of a coherent-state approach we extract potential-energy curves for these molecules.

The interaction of a four-level atomic system with two electromagnetic radiations has been studied. The two intermediate levels are closely spaced such that a single radiation frequency can induce transitions from the ground state to both of them. In a cascade-type double resonance, the pump electric-field amplitude is much stronger than the amplitude of the signal field, which can induce transitions from both of the intermediate levels to the upper state. The 15 optical Bloch equations obtained from the Liouville equations are solved analytically to obtain the Doppler-free signal line shape. The computed signals, exhibiting two Lorentzian line profiles, are presented for different pump frequencies. In addition to these one-photon transitions, we obtain a weak two-photon resonance peak. The two-photon resonance becomes weaker when the detuning of the pump frequency from a resonance frequency is increased. When the pump frequency ${\mathrm{\Omega }}_{\mathit{p}}$ is intermediate between the pump resonance frequencies ${\mathrm{\omega }}_1$ and ${\mathrm{\omega }}_2$, the two-photon resonance is very weak and almost vanishes when ${\mathrm{\Omega }}_{\mathit{p}}$=(${\mathrm{\omega }}_1$+${\mathrm{\omega }}_2$)/2. When the pump frequency is on resonance with one of the transition frequencies, the Rabi splitting of the signal shows asymmetry because of the presence of a close-lying transition which is pumped off resonance. The intensity-dependent shifts of the transitions are such that they repel each other more and more as the intensity of the pump field is increased. These shifts arise from the nonresonant interaction between the atom and the field.

High selectivity (>10) for separation of ${}_{}{}^{91}{}_{}{}^{}\mathrm{Zr}$ from other Zr isotopes was observed during triple resonant ionization of Zr vapors. Linearly polarized lasers were used to prepare aligned states, from which further excitation to a presently discovered J=0 level could be suppressed for even-mass isotopes, by a suitable choice of relative laser polarization. Photoionization of the odd-mass isotope ${}_{}{}^{91}{}_{}{}^{}\mathrm{Zr}$ could be retained by use of transitions with relatively strong hyperfine interactions, because of associated population redistributions in the magnetic sublevels. The dependence of the even-mass-isotope signals on relative laser polarization followed sinusoidal forms, which are in excellent agreement with predictions derived using only geometric components of the transition dipole moment. The isotopic selectivity for ${}_{}{}^{91}{}_{}{}^{}\mathrm{Zr}$ can be increased by use of saturating fluences, because of the effects of saturation, population trapping in the even-mass isotopes and strong hyperfine interactions in the odd-mass isotopes. For the same reasons, biases in even:odd isotope ratio measurements cannot always be eliminated by polarization scrambling or magic angles.

We report the energy and linewidths of the 7snf ${}_{}{}^{1,3}{}_{}{}^{}$${\mathit{F}}_3$ autoionizing states of barium with n values of 11–21 for the singlet states and 11–18 for the triplet states. Near n=16, the 7snf ${}_{}{}^1{}_{}{}^{}$${\mathit{F}}_3$ states are perturbed by the 6d9p ${}_{}{}^1{}_{}{}^{}$${\mathit{F}}_3$ state. The scaled linewidth of the unperturbed 7snf ${}_{}{}^1{}_{}{}^{}$${\mathit{F}}_3$ states is ${\mathit{n}}^{\mathrm{*}3}$Γ=γ=0.15, which is approximately half of the value for the $6_{1/2}$nf states. This suggests that the larger core size of the 7s core increases the core penetration of the Rydberg electron in the 7snf ${}_{}{}^1{}_{}{}^{}$${\mathit{F}}_3$ states, and thus reduces those autoionization rates.

In the first Born approximation, the laser-assisted rearrangement collision between a positron and a hydrogen atom is systematically studied. In solving the dressed wave functions, the A⋅p gauge is adopted. To overcome the difficulty in the reduction of the S matrix, we have developed the Feynman integration technique. The scattering amplitude is reduced to one-dimensional integrals and analytical expressions. The numerical calculation is greatly simplified, which makes it possible to compute the integral cross sections for Ps formation including multiphoton processes. Our results indicate that when the laser field is presented, the cross sections for Ps formation are remarkably enhanced. This is of great importance in improving this kind of reaction.

I propose a coherent atomic-beam splitter that can be used for atom interferometry. Chirped adiabatic passage between states of the atoms of the atomic beam is employed as they pass through a standing-wave radiation field to split coherently the atomic beam.

A numerical method to solve the Schrödinger equation for a charged particle in a Paul trap is suggested. The quantum secular motion approximation is examined by comparing the exact numerical solution with the approximate result. The stability of quantum motion of the particle is discussed.

The two-photon ionization rate for the lithium atom is calculated in the time-dependent Hartree-Fock approximation for a variety of intensities and photon frequencies. The time-dependent equation for the valence Hartree-Fock orbital is solved on a two-dimensional cylindrical-coordinate lattice using both fixed and variable grid spacings. The nonperturbative results are compared with previous perturbation-theory results at photon energies near the 2s→3p single-photon resonance.

We study theoretically the spectrum of resonance fluorescence and laser-cooling dynamics corresponding to quantized atomic motion in one-dimensional optical molasses. We consider an atom with a ${\mathit{J}}_{\mathit{g}}$=1→${\mathit{J}}_{\mathit{e}}$=2 transition interacting with two counterpropagating laser beams. The laser light is assumed to be linearly polarized with an angle θ between the polarization vectors. We discuss the spectrum of resonance fluorescence, the spectroscopy of band structure in the optical potentials, and the population of the vibrational quantum levels as a function of the angle between the polarization vectors.

We study the nonlinear behavior of the electric susceptibility for several systems showing a high index of refraction without absorption due to quantum coherence and interference. Estimates of cw intensity limits for a given index of refraction are obtained. We calculate critical field intensities for self-focusing and investigate the stability of the absorption cancellation with regard to intensity fluctuations.

We prove that the amplification condition for a multifrequency field in an atomic system with multiple splitting of the operating levels implies a population inversion between the eigenstates of the density matrix. This explains the possibility of amplification without population inversion when a coherent superposition state of sublevels is prepared.

Optical switching between bistable soliton states of the second kind is demonstrated numerically when the amplification of the input solitons is suitably adjusted. The numerical amplification study is supplemented by Anderson’s [Phys. Rev. A 27, 3135 (1983)] variational approach, which sheds considerable light on the observed numerical behavior, although it is not able to predict switching.

We present a generalized Jaynes-Cummings model (JCM) with an intensity-dependent coupling interacting with a quantum group-theoretic coherent state. The field operators of the JCM Hamiltonian are identified as the elements of the ${\mathrm{su}}_{\mathit{q}}$(1,1) quantum algebra in their Holstein-Primakoff realizations. We lay emphasis on the time evolution of field quadruatures and atomic population inversion of the generalized JCM. The revivals of radiation squeezing are obtained for any values of initial squeezing.

We show how a special class of Schrödinger macroscopic quantum-superposition states can be produced by a coherent field propagating through a Kerr medium. We show that these states are eigenstates of the mth power of the photon-annihilation operator leading also to the possibility of producing these using multiphoton Jaynes-Cummings systems. We further show how superpositions of squeezed coherent states can be produced.

We compare the quantum fluctuations in two commonly used models of the laser, the Haken-Lamb model [H. Haken, Laser Theory (Springer-Verlag, Berlin, 1984)] and the Lax-Louisell model [W. H. Louisell, Quantum Statistical Properties of Radiation (Wiley, New York, 1973)]. In the Haken-Lamb model the laser medium is taken to consist of two-level atoms whereas in the Lax-Louisell model it consists of three-level atoms. We compare the predictions of both models for the output statistics of the field in the limit where the atomic variables may be adiabatically eliminated. Our comparison is valid from near threshold to far above threshold. While the three-level model is the more realistic of the two, we find that the simpler two-level model gives good agreement for the amplitude noise, provided this decouples from the phase noise in a given system.

The temporal effects of multiphoton ionization are investigated using a two-color method which determines both the time and intensity at which the process occurs. We show that the total ionization efficiency depends strongly on the time at which an atom makes a transition to an excited state during an intense laser pulse. This result clearly shows that the ac-Stark-shifted bound-state resonances not only enhance the cross section for photoionization, but that the excited bound states provide temporary storage states for the atomic population during the photoionization process.

In the present paper, we report a theoretical description of the internal dynamics of one-dimensional molecular aggregates, subject to fluctuations of the excitation energy and site-site coupling. The role played by these diagonal and nondiagonal stochastic interactions on the nonlinear optical response of the aggregate is studied. As an example, the influence of these processes on the third-order hyperpolarizability is evaluated.