Control over product probabilities and channel-specific line shapes in resonant two-photon dissociation is shown to result from quantum interference effects induced by illumination with a second laser. Control over product yield and selectivity is achieved by varying the frequency of this control laser, which need not be coherent with the excitation laser. Computations on ${\mathrm{Na}}_2$ photodissociation show that control over product selectivity is extensive.

We present a theoretical construction for closest-to-classical wave packets localized in both angular and radial coordinates and moving on a keplerian orbit. The method produces a family of elliptical squeezed states for the planar Coulomb problem that minimize appropriate uncertainty relations in radial and angular coordinates. The time evolution of these states is studied for orbits with different semimajor axes and eccentricities. The elliptical squeezed states may be useful for a description of the motion of Rydberg wave packets excited by short-pulsed lasers in the presence of external fields, which experiments are attempting to produce. We outline an extension of the method to include certain effects of quantum defects appearing in the alkali-metal atoms used in experiments.

A theoretical nonperturbative study of the coherent excitation of a two-state system by N consecutive equally spaced identical pulses is presented. General relations between the evolution matrix elements in the cases of one and N pulses are obtained in a closed form. For pulse envelopes allowing analytical solutions, these relations enable analytical treatment of pulse-train excitation; for pulses that can only be treated numerically, they shorten the computations by a factor of N. The relations show that the multiple-pulse excitation of a two-state system can be considered as a quantum analog of the diffraction grating. The interaction dynamics substantially depends on the way the train is produced because the phase shift that is accumulated by the probability amplitudes due to the free evolution of the system during and between the pulses differs. In the limit of weak excitation, the results recover earlier conclusions based on perturbative treatments. Simple formulas are derived for the conditions for complete population inversion (CPI) and complete population return (CPR), which differ from the single-pulse ones. These general results are applied to four particular cases that allow analytical solutions: resonant, rectangular, Rosen-Zener, and Allen-Eberly pulses. A common feature in all these cases is that the number and the amplitude of oscillations in the state populations increase with the number of pulses, while their width decreases. For rectangular pulses, CPI is possible below a given value of the ratio between the detuning and the pulse area; this value increases nearly linearly with the number of pulses.

For the Rosen-Zener model, CPI is found to be possible for two and more pulses, while it is impossible for a single non-resonant pulse. It is shown that for a given number of pulses there is an upper limit on the detuning for which CPI can be observed; this limit increases logarithmically with the number of pulses. For the Allen-Eberly model, CPR is established to be possible for more than one pulse, while it is impossible for a single pulse. The cases of even and odd number of pulses are shown to lead to substantially different results. The limitations imposed on the detuning by the conditions for CPR and CPI are derived and discussed.

Emission rates for high-harmonic generation by a zero-range-potential model atom in the superposition of two monochromatic plane-wave fields are calculated. Several polarizations of the driving fields are considered: two linear polarizations enclosing an arbitrary angle, and two circularly polarized fields that co- or counter-rotate in the same plane. Transition amplitudes are obtained in the form of sums of one-dimensional integrals that have to be computed numerically. For commensurate frequencies of the driving fields the results depend critically on the relative phase between the two fields. Parallel driving fields are not always more efficient in harmonic generation than perpendicular fields; also, two circular polarizations can be at least as effective. The odd harmonics of one field are usually weakened by the addition of the other field in favor of the mixed harmonics. If the ratio of the frequencies of the two incident fields equals the ratio of two odd integers, then harmonics with elliptic polarization can be generated by two linearly polarized driving fields. Harmonics with circular polarization can readily be produced with the help of two incident circularly polarized fields whose field vectors co-rotate or counter-rotate in the same plane.

Laser-induced autoionization, a form of forced autoionization, is discussed. Highly excited atomic Rydberg states generally have a small cross section for photoionization due to their small overlap with the nucleus. The cross section for photoionization can be strongly enhanced if the Rydberg series is perturbed by an atomic state with a relatively large cross section for photoionization. The photoionization dynamics of such a perturbed Rydberg system shows strong similarities to that of an autoionizing Rydberg series. For intense laser pulses, which strongly couple the perturber to the continuum, the photoionization rate is limited by the coupling between the Rydberg states and the perturber or, in other words, the autoionization rate. The model describing this ionization dynamics is applied to the barium 6snd${(}^{1,3}$${\mathit{D}}_2$) state which is perturbed by the 5d7d${(}^1$${\mathit{D}}_2$) state. The calculations show good agreement with experimental results of photoionization of barium Rydberg states with subpicosecond laser pulses of light of 620 nm in wavelength.

We study the dynamics of radial wave packets in the singular Coulomb potential by solving the time-dependent Schrödinger equation numerically. A propagation scheme involving fast-Fourier transforms is used. We concentrate on the simple radial motion of the hydrogen atom to test the numerical method. In particular, we calculate the dynamics under the influence of a strong laser pulse and document how above-threshold-ionization peaks can be interpreted in terms of momentum-space wave functions. The results are compared to those obtained from a calculation that uses a soft core potential.

The Λ system resulting from the interaction of counterpropagating orthogonally polarized beams of light with a ${\mathit{J}}_{\mathit{g}}$=1→${\mathit{J}}_{\mathit{e}}$=1 transition is known to exhibit laser cooling without the presence of a damping force, through velocity selective coherent population trapping. This occurs independent of the sign of the laser’s detuning from the atomic resonance frequency. We present measurements and calculations that show a detuning-dependent transient peak or dip in the ground-state momentum distribution centered at ${\mathit{p}}_{\mathit{g}}$=0, however, which is reminiscent of laser cooling by a damping force. We explain this in terms of the character of the quantum-mechanical eigenstates of the total ground-state Hamiltonian of the system, using both analytic expressions and numerical calculations.

A theoretical and experimental investigation has been carried out into the viability of V-type, Λ-type, and cascade systems within rubidium for the observation of electromagnetically-induced transparency (EIT). A Λ-type system is also discussed where EIT is induced on a two-photon transition. Continuous-wave single-frequency titanium sapphire lasers have been employed to provide the applied optical fields. It is found that systems that have a strong coupling field resonant with the 5${\mathit{S}}_{1/2}$ ground state suffer from complicating optical pumping mechanisms that tend to mask EIT windows. It is also found that wavelength matching of the applied optical fields enhances the observation of EIT since this results in a reduced residual Doppler linewidth of the atomic system.

We present a simple theory on the effect of optical dephasing on the spontaneous emission (SE) rate in a microcavity containing (absorbing) dispersive dielectric media based on a photon Green’s-function formalism in which the reservoir damping of medium polarizations is included in a phenomenological way. The theory yields the well-known result that the SE rate in free space is modified by the real part of the refractive index at the transition frequency of an atom in a bulk dielectric. On the other hand, it turns out that the degree of the alteration of the SE rate in a high-Q microcavity with dispersive media is affected not only by the real part of the refractive index but also by the imaginary part of the refractive index that is associated with the dephasing of the photon field due to the reservoir damping, i.e., the destruction of self-interference of the photon field.

The position as well as the width of the atomic wave packet passing through an optical cavity may affect the matter-field interaction. As a result, the internal dynamics of a two-level atom, such as the Rabi oscillations or the collapse and revival phenomenon, may be strongly modified with respect to the standard Jaynes-Cummings model. In particular, for a sufficiently large spread of the atomic position, the atomic population inversion displays the characteristic ringing behavior of the Bessel function ${\mathit{J}}_0$ differently from the usual full Rabi oscillation.

The dynamics of a Brillouin fiber ring laser operating on the two first Stokes components is studied both theoretically and experimentally. The emergence of the second order Stokes wave is described within the framework of a coherent five-wave model that generalizes the usual three-wave model. The laser steady states are analytically characterized and the dynamics is numerically studied. The laser emission is stable except at high pumping rates for which the system exhibits periodic and quasiperiodic instabilities. Experimental results are in good agreement with the theoretical predictions.

A class of coherent states defined in terms of the excitation and deexcitation of pairs of photons is studied with reference to its nonclassical and other quantum-statistical properties. These states supplement the other well-known two-mode states such as Caves-Schumaker states and pair coherent states and can be produced by dissipative processes involving emission and absorption of photons in pairs.

We propose a description of the collective atomic-recoil laser based on a set of nonlinear differential equations for an appropriate set of collective variables. The main obvious advantage of this description is that, when applicable, it can describe systems having an arbitrary number of particles. A comparison between the predictions of the collective equations and those of their microscopic counterparts shows a satisfactory level of accuracy, even during the nonlinear stage of the evolution. The linearized version of the collective equations is especially useful for the study of the small-signal gain or absorption spectrum and the analysis of the start-up process.

We consider a phase-sensitive amplifier that consists of a system of three-level atoms in a cascade configuration that is prepared in a coherent superposition of upper and lower states by a strong classical field. We have studied the role of pump phase fluctuations associated with the finite linewidth on the quantum-statistical properties of the radiation field. A study of the output field characteristics reveals that the presence of a very weak pump field gives rise to equal variances in both field quadratures which are independent of linewidth. On the other hand, the presence of a strong pump field alters the output field characteristics with the generation of squeezing which is later on destroyed due to the presence of phase fluctuations.

We derive a master equation for the dynamics of a maser or laser with periodic injection of excited atoms. The model includes regular pumping with single atoms, but it also covers the case of periodic injection of groups of atoms, whose number may fluctuate. To obtain a quasicontinuous master equation for such a periodically kicked dynamics, we consider a macroscopic state of the field that is obtained from the true microscopic state by a time average over many periods. The master equation for that time-averaged state correctly describes both the stationary and the transient properties of the maser on a coarse, macroscopic scale. Numerical and analytical results based on this equation are compared with a microscopic, step-by-step resolution of the field’s evolution along the periods. Deviations from the microscopic results only occur when frequencies of the order of the (mechanical) injection frequency of the pump become relevant. The recently predicted regularity-induced line splitting in the emission spectrum of a maser is an example for such a situation.

We develop a general theory for noise fluctuations in open optical systems with gain or loss based on an expansion in terms of nonorthogonal quasimodes. Spatial variation of the index of refraction and of the gain are taken into account. We show that below threshold, i.e., when the system is linear, this method is formally equivalent to using Green’s matrices. We calculate the modes and the fluctuation spectra above threshold for a distributed-feedback laser including gain saturation effects.

We predict the effect on the intracavity quadrature-phase-amplitude probability distribution of coupling the signal mode of a degenerate parametric oscillator to a squeezed bath. Solutions in a transient regime reveal interference fringes which are indicative of the formation of a ‘‘Schrödinger cat’’ state. The use of the squeezed reservoir allows fringes to be predicted for smaller nonlinearity-to-loss ratios.

We analyze the Fresnel number and gain dependence of the spatiotemporal dynamics of a dye laser. The results support the existence of ordered behavior in the low-Fresnel-number and low-gain regions and a transition to spatiotemporal disorder when the Fresnel number and/or the gain are increased. The disordered state has a surprisingly small correlation length (much smaller than the system size), supporting the idea that turbulence is possible in laser systems.

The superposition of input fields in a lossless beam splitter is studied in the Schrödinger picture by using the convolution of the positive P representations, and the convolution law for these representations is extended to other quasiprobability functions such as the Wigner and Q functions. We show that the reservoir can be modeled by an infinite array of beam splitters, and we use the convolution law and this model to derive the Fokker-Planck equation for a system coupled with a phase-sensitive reservoir. Solving this equation shows that a phase-sensitive attenuation and amplification can be described by the superposition of two independent quantum fields, one of which is the initial signal field and the other the squeezed thermal noise field representing the reservoir.

The photorefractive two-wave mixing gain coefficient Γ of GaAs:Cr and InP:Fe, cut with different crystallographic orientations, was determined using a cw Nd:YAG (neodymium doped yttrium aluminum garnet) laser at 1064 nm. The polarization and orientation dependence of the gain coefficient Γ are calculated from the pertinent interaction matrix elements. Results are discussed with respect to the contactless determination of crystallographic parameters via the photorefractive effect.