We present an analysis of the factors that affect selectivity in resonant multiphoton ionization. After a discussion of the formalism in terms of the density matrix in the context of two-photon-resonant three-photon ionization, we apply the theory to Li and Sr, demonstrating the effects of laser bandwidth, power broadening, and pulse duration.

A theoretical treatment is given of the process in which the two photons produced simultaneously in the parametric frequency splitting of light are allowed to interfere. It is shown that, while there is no interference in the usual sense involving quantities that are of the second order in the field, fourth-order interference effects are present. These may be revealed by measuring the joint probability of detecting two photons at two points x,x’ in the interference plane with photoelectric detectors as a function of the separation x-x’. The probability exhibits a cosine modulation with x-x’, with visibility that can approach 100%, even though the integration time in the experiment may greatly exceed the reciprocal bandwidth of the photons. The interference effect has a nonclassical origin and implies a violation of local realism in the highly correlated two-photon state.

We derive and discuss the dissipative effects of a heat bath on a nonlinear oscillator, excluding very low temperatures [kT≲(level width )] such that a Markovian master equation holds. For temperatures high enough for excited states of the oscillator to acquire noticeable thermal population we find the nonlinearity to have a drastic influence on transition rates and level shifts.

The output state of a nonlinear Mach-Zehnder interferometer is shown to be an effective number-phase minimum-uncertainty state with reduced photon-number uncertainty. This interferometer includes an optical Kerr medium in one arm with a coherent-state input. Unusual ‘‘crescent’’-shaped squeezing which preserves photon number is revealed in the unitary evolution associated with a self-phase-modulation in the Kerr medium. Photon-number uncertainty 〈Δn${^}^2$〉 can be reduced by interference with a coherent-state reference wave. It can be minimized to 〈n^${〉}^{1/3}$, far below the limit 〈n^${〉}^{2/3}$ achieved by an ordinary squeezed state. The increased phase uncertainty due to self-phase-modulation and the reduced photon-number uncertainty still preserve the minimum-uncertainty product 〈Δn${^}^2$〉〈ΔΦ${^}^2$〉∼(1/4). .AE

A high-resolution study of magnetic-field-induced second-harmonic generation in sodium vapor has been carried out with use of a single-frequency continuous-wave dye laser. Resonant enhancement was obtained by tuning the laser to the frequency of the 3S→4D two-photon transition of the sodium atom. Experimental and theoretical results are presented showing the variation of the power and polarization properties of the second-harmonic radiation as the laser is tuned across the two-photon resonance, and as the transverse magnetic field is varied.

Suitable equations for lasers with injected signal are derived in the case of a population decay much slower than the other damping processes. A perturbative approach for a small input field ɛ shows evidence of anomalous pushing of the laser frequency away from the external reference one. A threshold for the appearance of antisynchronized solutions is analytically found and numerically checked. A double-point bifurcation explains the switch from pulled- to pushed-frequency solutions as an exchange with a second branch of auto-Q-switched periodic trajectories. The final analysis of locking threshold allows us to relate the small- and large-ɛ behavior.

We present in this paper a theoretical and experimental study of the effect of an intense pump beam on four-wave-mixing emission in the geometry of phase conjugation. The theoretical model is developed for Γ (natural width) <${\Omega }_1$ (Rabi frequency of the intense pump) <ku (Doppler width) and uses the dressed-atom approach. We have analyzed degenerate and nearly degenerate four-wave mixing. In this latter case, we have studied three situations according to which beam (intense pump, weak pump, or probe) has a different frequency. The experimental study has been done in a neon cell using cw lasers. Our experimental results are in excellent agreement with theory. This study shows the need to take into account the atomic motion in the theory. However a quantitative analysis cannot be done assuming an infinite Doppler width and we show the importance of the Boltzmann factor. In the case of nearly degenerate four-wave mixing, narrow resonances corresponding to transitions between energy levels of the dressed atom are observed.

This paper clarifies the origins of the standard quantum limit for the amplitude noise of a laser-oscillator outgoing field. The amplitude noise within the cavity bandwidth, Ω≤ω/Q, is ultimately caused by the pump amplitude fluctuation, while that above the cavity bandwidth, Ω≥ω/Q, is due to the field zero-point fluctuation. The uncertainty product of the amplitude- and phase-noise spectra at an extremely high pumping level is still larger than the Heisenberg minimum-uncertainty product because of the presence of nonstationary phase-diffusion noise. In this sense, an ordinary laser oscillator is not a quantum-limited device. This paper suggests that a laser oscillator can produce an amplitude-squeezed state in itself if the pump amplitude fluctuation is suppressed below the ordinary shot-noise level. The paper discusses possible schemes for suppressing pump fluctuation, commutator bracket preservation without pump fluctuation, and resulting amplitude and phase spectra. The similarity of and difference between a pump-noise-suppressed laser and a cavity degenerate parametric amplifier are delineated.

We show that, in principle, an active gravity-wave detector based on a correlated-spontaneous-emission laser has potential advantages over the more usual passive scheme.

A general quantum theory of nonlinear mixing in multimode fields is formulated. The theory is valid for arbitrary media and thus includes various diverse cases such as those corresponding to nonlinear mixing in multilevel systems, optical fibers, etc. Thus Zeeman coherence effects are automatically included. It is applicable to both degenerate and nondegenerate mixing experiments. The theory is in terms of two distinct sets of correlation functions of the polarization operators. One set of correlations is related to the nonlinear susceptibilities. The other set has no counterpart in semiclassical theory and is related to the quantum-mechanical fluctuations of the polarization operator. The general structure of the evolution of the density matrix of the generated fields is discussed. The quantum statistics of the generated fields can be studied in terms of the Wigner distribution function which is explicitly evaluated. Higher-order squeezing characteristics of the field are discussed. Conditions under which the quantization of the semiclassical equations is adequate are examined. The application of the quantum theory to nonlinear mixing in two-photon media is also presented. The theory is also capable of accounting for the interparticle correlations.

We present in this paper a new method, wave-function recoupling in a many-atom system, in solving the resonance fluorescent spectrum. For a two-atom system, if the influence of stimulated emission on the cooperative effect is taken into account, the resonance fluorescence spectrum is expected to display five peaks. For a frequency-detuning case, an obvious asymmetry may appear in the spectral intensity distribution.

A physical interpretation of the diffusion-limited-aggregation (DLA) algorithm for simulating viscous fingering during fluid displacement in a porous medium is given in terms of the material properties of the porous medium. In one dimension, the flow patterns generated by a DLA simulation correspond to a simple exponential distribution of ‘‘fluid capacity.’’ Also, for any given distribution of fluid capacity, it is possible to establish a corresponding stochastic algorithm for the moving fluid interface. The discussion of this paper places the DLA simulation of viscous fingering on a physical basis and, more generally, establishes the mathematical equivalence of two models of stochastic interface evolution.

An expression for the relativistic ponderomotive Hamiltonian for magnetized particles of a cylindrical waveguide mode is derived. From this result, the equations of motion for the beam particles and the beam Vlasov susceptibility are obtained. The expression for the ponderomotive Hamiltonian is then taken in the limit of unmagnetized particles and used in an analysis of charged-particle-beam confinement by ponderomotive force due to a waveguide mode. Formulas for the rf power and energy density inside the waveguide needed to confine a beam with a given kinetic energy and current are then derived. Numerical estimates give reasonable values for the rf power and energy needed to confine a typical electron or ion beam.

This paper discusses the evaluation of a joint probability distribution depending on the position of the nearest perturbing ion to an atomic radiator and the electric field due to all other ion perturbers. Possible applications for the distribution are use in calculating line-broadening effects due to ion quadrupole and higher-order multiple interactions and ion-radiator dynamics.

Measurements of the Hg (253.7 nm) output ($P_{\mathrm{uv}}$) and output per arc watt ($P_{\mathrm{uv}}$/$P_W$) as a function of ${}_{}{}^{196}{}_{}{}^{}\mathrm{Hg}$ concentration in a low-pressure Hg-Ar electrical discharge are reported. A peak increase of 7.9% and 6.8% for $P_{\mathrm{uv}}$ and $P_{\mathrm{u}\mathrm{v}/\mathrm{PW}}$, respectively, has been found at 2.6 wt. % ${}_{}{}^{196}{}_{}{}^{}\mathrm{Hg}$. A modified Holstein-Biberman formalism that takes into account emission and absorption line shapes, energy transfer between Hg isotopes, rare-gas hyperfine mixing, and overlap between different isotopic components has been developed. Based on this formalism the calculated hyperfine structure (hfs) of the Hg(6 ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$→6 ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$) transition is in very good agreement with our measured hfs. Furthermore our calculations predict a saturation in $P_{\mathrm{uv}}$ and $P_{\mathrm{uv}/P_W}$ for relatively low ${}_{}{}^{196}{}_{}{}^{}\mathrm{Hg}$ concentrations. This formalism is applicable to various problems involving resonance radiation transfer in metal-vapor–rare-gas combinations containing more than one isotope.

An experimental study is presented of heating of gold plasma by a Raman-compressed KrF laser (2-ns full width at half maximum, λ=268 nm) in the intensity range of 5×${10}^{11}$–2×${10}^{13}$ W/${\mathrm{cm}}^2$. Measurements of electron temperature and its scaling with laser intensity, angular distribution of plasma energy and ion blowoff velocity, and keV x-ray emission are performed and compared with those for an aluminum plasma heated under the same experimental conditions. Strikingly different characteristics observed in the high-Z gold plasma are discussed in terms of radiation loss and radiative energy transport.

A closed, energy-conserving system of equations is derived describing the growth of the plasma beat wave and the decay of the driving electromagnetic pulse in the plasma-beat-wave accelerator. With the approximation that the electromagnetic phases are frozen, the pump-depletion equations are solved to determined the pump-depletion distance. A condition for minimizing the wake of plasma waves and maximizing the coherent acceleration length for the system is derived.

We report results of theoretical and computer-simulation studies of collision-induced light-scattering (CILS) intensities in fluids of optically isotropic molecules. Depolarized Rayleigh scattering in monatomic and spherical-top polyatomic fluids and depolarized Raman scattering at the completely symmetric vibrational mode of spherical-top molecular fluids are considered. Lennard-Jones potential is used to model intermolecular interactions. The collective polarizability is described by the first-order dipole–induced-dipole (DID) interaction model. CILS intensities for this model are evaluated by molecular-dynamics (MD) simulation at two temperatures and a set of densities. These results and those of earlier MD simulations are compared to the lattice-gas approximation to the same model. Results for the lattice-gas model (LGM) are obtained by Monte Carlo simulation on a face-centered-cubic lattice with Lennard-Jones and DID interactions between occupied nearest-neighbor sites. We find that the MD results for CILS intensities are weakly temperature dependent and that they agree well with the high-temperature version of the LGM. We also find that the LGM predicts a strong temperature dependence of these quantities, in disagreement with the MD results. Reasons for the inaccuracy of the LGM predictions and possible improvements of this model are discussed.

Iglesias [Phys. Rev. A 27, 2705 (1983)] has reformulated the problem of calculating the electric-microfield distribution in a plasma so that it is equivalent to finding the pair-distribution function of a fluid interacting through a complex potential. We solve the mean spherical model for such a fluid analytically and find that the microfield distribution so obtained is Gaussian with exact second moment.

We calculate the effective diffusion coefficient in convective flows which are well described by one spatial mode. We use an expansion in the distance from onset and homogenization methods to obtain an explicit expression for the transport coefficient. We find that spatially periodic fluid flow enhances the molecular diffusion D by a term proportional to $D^{\mathrm{-}1}$. This enhancement should be easy to observe in experiments, since D is a small number.