Multiple-pulse coherent averaging methods are used to increase the resolution and frequency range of optically pumped xenon NMR in nutation and point-by-point precession experiments. We observe quadrupolar splittings in ${}_{}{}^{131}{}_{}{}^{}\mathrm{Xe}$ spectra due to the macroscopic asymmetry of pumping cells similar to those reported previously, but with reduced demands on magnetic-field homogeneity. Cell treatment with hydrogen gas increases the quadrupolar splittings by a factor of 3 over bare Pyrex cells.

The phenomenon of stabilization of highly excited states of a hydrogen atom in a strong monochromatic field is discussed. An approximate description of the dynamics from the introduction of the Kramers map allows one to understand the main properties of this phenomenon through analogy with the Kepler map. The analogy between the stabilization and the channneling of particles in a crystal is also discussed.

We study the dynamics of chirped adiabatic passage (CHIRAP) with temporally delayed pulses to selectively and fully transfer population in atoms and molecules. We show that the transfer of population via stimulated Raman adiabatic passage (STIRAP) and stimulated two-photon adiabatic absorption with temporally delayed laser pulses is not adversely affected by applying a chirp to the pulses, provided the intensity of the laser is sufficiently large to allow adiabatic passage. We then proceed to consider systems in which a near degeneracy of terminal state levels results in nonselective population of the terminal levels using nonchirped STIRAP or two-photon absorption stimulated passage, because the dynamics within the nearly degenerate pair of levels is not adiabatic. However, the CHIRAP process selectively populates only one of the terminal levels.

We present a formal theory and detailed calculations for phase-dependent laser-atom interactions involving autoionizing states. First, through simple models, we demonstrate that the simultaneous one- and three-photon excitation of one or two neighboring autoionizing states can exhibit profound changes of the line shape, as the relative phase of the two fields is varied from 0 to π. Through a proper choice of the field intensities and the phase, we obtain analytical results showing that one can cancel the transition to the discrete or the continuum part of the wave function, thereby leading to a flat or a completely symmetric line shape, respectively. At higher intensities, additional effects come into play, providing additional coupling between the discrete and continuum parts, which also exhibits a phase dependence. Finally, our theory is applied to a much more complex situation in Xe, involving many channels, not amenable to simple analytical expressions, but exhibiting nevertheless equally profound effects, including a modification of the branching ratio of two different products. The theory, which is here developed for atomic autoionization, is in fact fairly general and should pertain to related problems in any system involving discrete states embedded in continua.

The effects of velocity-selective optical pumping in nearly degenerate four-wave mixing are studied using a model in which the radiation fields interact with ‘‘three-level’’ atoms in the Λ configuration. The conditions under which it is possible to observe resonances characterized by an effective ground-state width are explored. It is shown that saturation of the system by optical pumping can lead to the disappearance of these narrow resonances in some limiting cases.

A recent discovery by Hardy [Phys. Rev. Lett. 71, 1665 (1993)] is developed and extended. It shows that the inconsistency between quantum mechanics and Einstein-Podolsky-Rosen assumptions about locality and reality can be demonstrated for two photons or particles with spin 1/2, as in experiments that test Bell inequalities, but without inequalities, as in what Greenberger, Horne, and Zeilinger discovered for three or four particles [in Bell’s Theorem, Quantum Theory, and Conceptions of the Universe, edited by M. Kafatos (Kluwer, Dordrecht, 1989), p. 74]. Here all the possibilities are found. The measurement choices can be different for the two particles. They are described directly in terms of angles for spin measurements. Hardy’s result and its converse are both proved: almost any state will do (with measurement choices made to accommodate) and any choice of two different measurement possibilities for each particle will do (with a state made to accommodate). A simple example is given; it allows the calculations to be done quickly with Pauli matrices.

It is shown theoretically that Ramsey fringes can be produced when a laser-assisted reaction of the form ${\mathrm{A}}_2$+${\mathrm{A}}_1^{\prime }$+ħΩ→${\mathrm{A}}_1$+${\mathrm{A}}_2^{\prime }$ is driven by a pair of ultrafast radiation pulses, each of whose temporal widths is less than the duration ${\mathrm{\tau }}_{\mathrm{c}}$ of a collision between the A and A′ atoms. The excitation profile of the laser-assisted collision is calculated as a function of detuning of the laser field frequency from the initial- to final-state transition frequency. For radiation pulses separated by time T, Ramsey fringes appear separated in frequency by ${\mathrm{T}}^{\mathrm{-}1}$. The modulation depth and shift of the central Ramsey fringe as a function of (T/${\mathrm{\tau }}_{\mathrm{c}}$) provide information about the collisional interaction. Both the weak- and strong-field regions are considered and comparison with laser-assisted collisions using excitation pulses having temporal widths greater than ${\mathrm{\tau }}_{\mathrm{c}}$ is made.

Interaction of the one-dimensional (1D) Coulomb atom with an intense radiation field is analyzed using the ‘‘hard’’ Coulomb potential ${\mathit{V}}_{\mathit{c}}$(x)=-1/‖x‖ and the ‘‘soft’’ Coulomb potential V(x)=-1/ √${\mathit{x}}^2$+1 . Evolution of the probability wave packet and the photoelectron spectra is simulated numerically. In strong fields it is found (a) that the electron wave packet can break up into individual subpackets, (b) that there is a one-to-one correlation between the subpackets in space and the above-threshold-ionization peaks in energy, and (c) that a spatial confinement of the probability density can occur at a very high intensity. Finally, an example is given which indicates that the 1D ‘‘hard’’ Coulomb atom is less stable than the 1D ‘‘soft’’ Coulomb atom.

Experimental investigations of the laser-induced continuum structure in the vicinity of autoionizing states (AIS’s) of Ca are reported for both ionization and third-harmonic generation. The shape of the induced structures is shown to be strongly affected by the presence of the AIS’s, as well as exhibiting a detuning- and laser-intensity-dependent transition from a window resonance dip to a peak. The observed modification of the continuum is discussed in terms of interfering excitation channels.

A splitting in the Q distribution functions for the Jaynes-Cummings model is explained, based on the interpretations of the density matrix. It has been shown [J. Eiselt and H. Risken, Phys. Rev. A 43, 346 (1991)] that the Q function splits into two peaks, which counterrotate in phase space and that the collision on the opposite side of the space and the behavior of the Q function are closely connected to the collapse of the Rabi oscillations. This paper reveals the origin of the splitting of the Q distribution functions in terms of the interpretation of the density-matrix formalism. The effects of the initial atomic state on the Q distribution functions and on the quadrature fields are emphasized. It will be shown that the nonrotating Q function is responsible both for the collapse and revival of the Rabi oscillations and for the high-frequency components of the quadrature fields. In this analysis it is assumed that the initial light field of the model is a coherent state and that an atom is prepared in a coherent superposition of the excited and ground states. Three-dimensional figures of the Q distribution functions are presented as a function of the interaction time.

A theoretical study is presented of the gain profile and noise spectrum in the vicinity of the longitudinal-mode frequency separation of a single-mode laser amplifier of class A or class B. The gain and the noise are associated with the adjacent subthreshold modes on either side of the lasing mode; coupled equations of motion for these three modes have been solved. The amplitudes of the contributions of each individual subthreshold mode to both the gain and the noise are generally anticorrelated. Thus striking cancellation effects should occur in self-heterodyne measurements from the superposition of these contributions. The theoretical predictions are compared with the results of a parallel experimental study on a single-mode argon-ion laser amplifier. Measurements of the gain profiles and noise spectra close to the longitudinal-mode separation are reported for a range of laser output powers. Results are presented for simultaneous detection of the contributions of the two adjacent modes; for detection of only one adjacent mode, the other being suppressed with a Fabry-Pérot étalon; and again for detection of both modes but with their phase relative to the central laser beam modified by a Fabry-Pérot phase shifter. The predicted cancellation effects are clearly confirmed, and the gain profiles and noise spectra are in good agreement with the theoretical expressions. The noise-cancellation effect is demonstrated by the generation of an optical ‘‘antinoise’’ beam that is nearly 180° out of phase with respect to a broadband noisy input beam.

We investigate the properties of angular-momentum states which yield high sensitivity to rotation. We discuss the application of these ‘‘squeezed-spin’’ or correlated-particle states to spectroscopy. Transitions in an ensemble of N two-level (or, equivalently, spin-1/2) particles are assumed to be detected by observing changes in the state populations of the particles (population spectroscopy). When the particles’ states are detected with 100% efficiency, the fundamental limiting noise is projection noise, the noise associated with the quantum fluctuations in the measured populations. If the particles are first prepared in particular quantum-mechanically correlated states, we find that the signal-to-noise ratio can be improved over the case of initially uncorrelated particles. We have investigated spectroscopy for a particular case of Ramsey’s separated oscillatory method where the radiation pulse lengths are short compared to the time between pulses. We introduce a squeezing parameter ${\xi }_{\mathit{R}}$ which is the ratio of the statistical uncertainty in the determination of the resonance frequency when using correlated states vs that when using uncorrelated states. More generally, this squeezing parameter quantifies the sensitivity of an angular-momentum state to rotation. Other squeezing parameters which are relevant for use in other contexts can be defined. We discuss certain states which exhibit squeezing parameters ${\xi }_{\mathit{R}}$≃${\mathit{N}}^{\mathrm{-}1/2}$. We investigate possible experimental schemes for generation of squeezed-spin states which might be applied to the spectroscopy of trapped atomic ions. We find that applying a Jaynes-Cummings–type coupling between the ensemble of two-level systems and a suitably prepared harmonic oscillator results in correlated states with ${\xi }_{\mathit{R}}$<1.

We show that parametric interactions in quadratic nonlinear media can support a novel type of spatial dark soliton. In contrast to the conventional dark soliton in cubic nonlinear media, the most unique feature of the new soliton can be seen in the twin holes in its intensity profile. With a typical nonlinear material, a way to generate the soliton is proposed. A higher-dimensional extension of it is discussed.

We report results on different types of two-photon correlations for the micromaser field. We calculate these two-time correlations using the master equation for the micromaser field. We also present detailed results on the behavior of the eigenvalues of the Liouville operator for a range of excitation conditions and cavity parameters. We demonstrate the antibunching and the multiple-exponential decay of the micromaser field. We also discuss probing of the two-photon correlations.

For a sufficient number of atoms and in the framework of a semiclassical two-level model the beam maser exhibits multiple, steady-state intensity branches. We investigate the field evolution along the specific branches of the system and discuss the physics of transitions between these branches. We find that branch hopping, hysteresis, and bistability are present under high-cavity-Q conditions and that relaxation frequency shifts occur at crucial values of the excitation when these branch transitions take place. Spectra, phase-space portraits, and temporal behavior of the output field are analyzed. Dimensional analysis reveals the fractal dimension of a chaotic trajectory. Experimental conditions for the beam maser are examined.

We have studied theoretically a phase-conjugate ultrafast modulation spectroscopy (PCUMS) in a Doppler-broadened system. The pump beams consist of two frequency components which drive two different transitions. It is found that the four-wave-mixing (FWM) signal exhibits damping oscillation as the relative time delay between two pump beams is varied, from which the energy-level splitting can be deduced. We have considered the cases that pump beams have either narrow band or broadband linewidth and found that for both cases a Doppler-free precision in the measurement of the energy-level splitting can be achieved. The advantage of PCUMS is that the energy-level splitting between states can be widely separated. Finally, the relationship between PCUMS and other Doppler-free techniques in frequency and time domains has also been discussed.

We present a general formalism describing the evolution of partially polarized light propagating in a medium with cubic nonlinearity. Within the ergodic approximation we found that totally polarized coherent single-mode light remains totally polarized, irrespective of the type of optical medium. Partially polarized light consisting of a mixture of a coherent component with a random one preserves its degree of polarization in a dissipation-free medium with isotropic nonlinearity, while only linear or nonlinear dissipation may lead to alteration of the degree of polarization. We also found that in some crystal symmetry point groups, a time-nonreversible optical response may be the only reason for an alteration of the degree of polarization.

An approach using the generalized method of integral equations by substitution of the variables in the integral equation is applied to two- and quasi-two-dimensional systems. As a result, the connection between the integral and Maxwell equations as well as an extinction theorem for this case are established. The technique developed may be applied to any composite medium with a columnlike mesostructure. By use of the elementary cylinder radiator (‘‘mesoscopic atom’’) concept we reduce the problem of finding the optical properties of such media to the calculation of the susceptibility of a dense two-dimensional gas. The calculated optical anisotropy depends dramatically not only on the concentration but also on the form of the inclusions (mesostructure). Our calculations of the dielectric permittivity tensor for a two-dimensional composite medium with wire mesostructure show excellent agreement with the experimental measurements of the long-wavelength dielectric constants for two orthogonal polarizations in a photonic crystal made of dielectric rods [W. M. Robertson et al., J. Opt. Soc. Am. B 10, 322 (1993)].

We analyze the Risken-Nummendal–Graham-Haken instability occurring in a homogeneously broadened two-level unidirectional ring laser modeled by the Maxwell-Bloch equations. We investigate the class-B limit of these equations, and obtain analytically the bifurcation equation for all time-periodic traveling-wave solutions. Class-B lasers are characterized by slowly decaying oscillatory transients due to the small ration of population to cavity lifetimes; these include a number of practically important lasers such as ${\mathrm{CO}}_2$, solid-state, and semiconductor lasers. We then explore the bifurcation equation and note unusual properties for the direction of bifurcation. Of particlar interest is the condition for a supercritical Hopf bifurcation that contrasts to the known subcritical bifurcation of the single-mode laser. In addition, we examine the small-wave-number limit for the Hopf bifurcation.

The form of the molecular vibrational wave packet that is generated when a short laser pulse excites a Franck-Condon transition is examined. Particular attention is paid to the case when the vibrational potentials in the ground and excited electronic states have different characteristic frequencies and the exciting pulse duration is sufficiently long that the nuclei move during the excitation. It is shown that both the nonadiabatic change in vibrational frequency and the vibrational dynamics can cause squeezing of the resulting wave packet. For a pulse of sufficiently short duration, and for molecules in which the nuclei are more tightly bound in the excited electronic state, the dynamical squeezing dominates that arising from the change of vibrational frequency.