A comprehensive study is made of the absorption spectrum of a weak-probe beam irradiating a two-level atom damped by a broadband squeezed vacuum and driven by a strong laser field. We show that for a resonant driving field whose phase does not coincide with the principal directions of the squeezing ellipse, the absorption spectrum is asymmetric and exhibits absorption-emission profiles at the Rabi sidebands. We find that this feature arises from unequal populations of the dressed states of the system, which occur when all components of the Bloch vector are coupled to the driving field. A symmetric spectrum with dispersionlike profiles at the Rabi sidebands is revealed for an off-resonant driving field. Furthermore, the spectrum may exhibit an emission profile at the central frequency, signifying an amplification of the probe beam. We point out that the amplification at the central component is not attributed to population inversion in both the atomic bare states and in the dressed atomic states. We find that the amplification originates from the coherent population oscillations and is impossible in the absence of the squeezed vacuum. In addition, we examine how these features are affected by the detuning of the driving field and an imperfect squeezed vacuum.

We consider two models of multimode lasers: the Tang-Statz-deMars equations modeling a solid-state Fabry-Pérot laser [C.L. Tang, H. Statz, and G. deMars, J. Appl. Phys. 34, 2289 (1963)] and the rate equations modeling intracavity second-harmonic generation in a Nd:YAG ring laser (where YAG denotes yttrium aluminum garnet). In both models, the dynamics is dominated by a global coupling of the modes of the electromagnetic field in the cavity. Although the equations for these two problems are fairly different, we prove that a dominant asymptotic approximation can be determined in each case that leads to the same conservative problem. It depends on one parameter, which measures the strength of the global coupling, and admits a class of antiphase periodic solutions.

We present theoretical and experimental second- and fourth-order interference patterns for entangled photons of different colors entering single and dual Mach-Zehnder interferometers in which dispersive elements have been deliberately placed. Although photon wave packets are generally broadened, as well as delayed, by passage through dispersive optical elements, coincidence measurements made with entangled photon pairs can be free of such broadening. This occurs for materials with particular dispersive behavior, as well as when the dispersion is balanced in both arms. This nonlocal behavior arises from the entanglement in the frequencies of the down-converted pair photons. We also show that nonlocal pump-frequency oscillations are present in the coincidence rate patterns for long path-length-difference times, confirming the robustness of this phenomenon in the presence of dispersion. However, the magnitude of these oscillations is reduced when an arbitrary dispersive material is used in an unbalanced configuration. Difference-frequency oscillations are also robust in the presence of dispersion, although they decay for large path-length-difference times.

We derive general solutions for the two-mode operators after two laser modes interact with a beam of atoms coherently prepared in the lower levels in the Λ scheme. It is shown that under certain conditions, a ‘‘noise-free’’ energy transfer can take place from a strong coherent mode to a weak squeezed-field mode.

This paper analyses the extraction of spectroscopic information on an atom via use of field fluctuations in a diode laser, wherein the statistics of diode-laser radiation are modeled by a phase-diffusion process. Using Monte Carlo methods, we solve density-matrix equations for a three-level V system, driven by this fluctuating field, tuned approximately to the two allowed transitions. The model is very general and allows us to incorporate arbitrary field strengths and bandwidths. We suggest two different signal detection schemes, each of which provides insight into different aspects of the energy-level structure in an atomic sample. Specifically, if intensity fluctuations in the field radiated from the sample are spectrally analyzed, via a homodyne technique, one can isolate contributions that are linear and quadratic in the radiated field, and these reveal resonances at the allowed transition frequencies of the atom. If we employ direct detection instead of the homodyne method, then the crossover transition is also revealed in the signal. The strengths of these resonances are very sensitive to the bandwidth of the field fluctuations, as well as the details of the field statistics. We also discuss the role of Stark shifts at higher intensities.

The geometry of a total-internal-reflection (TIR) phase-conjugate mirror is investigated in the framework of a two-dimensional model, based on the solution of nonlinear material equations and the parabolic equations for electromagnetic radiation. The model self-consistently describes the evolution of incoherent scattering into the spatial structure of light corresponding to the operation of the TIR mirror. We analyze the dynamics of nonlinear reflectivity and conjugation fidelity and their dependence on parameters of the problem, the spatial structure of fields and the nonlinear refractive index, and the typical distortions in the phase-conjugate output of the TIR mirror. Theoretical predictions are confirmed experimentally.

We develop a model of an experiment on pattern formation in a liquid-crystal light valve with single feedback mirror [E. Pampaloni et al., Europhys. Lett. 24, 647 (1993)]. An analytical treatment based on amplitude equations explains most of the observed phenomena. Saturation effects are needed to describe a secondary bifurcation between triangular and roll patterns.

The dark-soliton timing jitters caused by fluctuations in either the soliton initial phase angle or the background amplitude when such a soliton propagates in a monomode optical fiber under the influence of the stimulated Raman scattering are investigated and compared with those that exist when the stimulated Raman scattering is not present. In addition, it is demonstrated that in the presence of the stimulated Raman scattering, there exists a distance at which, for the negative soliton initial phase angle, the dark-soliton timing jitter caused by fluctuations in the background amplitude becomes zero.

We present analytical calculations of the turn-on-time probability distribution of intensity-modulated lasers under resonant weak optical feedback. Under resonant conditions, the external cavity round-trip time is taken to be equal to the modulation period. The probability distribution of the solitary laser results are modified to give reduced values of the mean turn-on-time and its variance. Numerical simulations have been carried out showing good agreement with the analytical results.

Using a perturbation method, constructed in terms of SU(2)-group representations, we investigate the time evolution of the statistics of photons spontaneously emitted by a system of N identical two-level atoms immersed in a single-mode ideal cavity with s atoms initially excited. The phenomenon of collective collapses and revivals is discussed and the collapse and revival times, which are different for odd and even s, are determined. It is shown for s extremely small compared to N that at appropriately chosen time instants the model generates the s-photon-number state (Fock state).

We investigate temporal effects in pulsed squeezing by parametric amplification, including effects of group-velocity dispersion. Our calculations show that the local oscillator pulse used to detect the squeezed field cannot be made shorter than the inverse phase-matching bandwidth of the generation process without degrading the amount of squeezing detected. This result generalizes an earlier result that showed that in the absence of dispersion, the local oscillator pulse duration should approach zero for optimum squeezing detection. We further show that by using local oscillator amplitude and phase pulse shaping it should be possible to achieve more than 40 dB of detectable quadrature squeezing. This is applicable where it is possible to neglect transverse spatial dimensions and diffraction, such as in a waveguide. We derive the s-parametrized quasiprobability evolution equation for the traveling-wave parametric amplifier. As the Wigner representation results in third-order derivatives, we also use the positive-P representation as an exact representation with equivalent Ito stochastic differential equations. This allows us to compare approximate — but easily simulated — Wigner representation results with those using the positive-P representation.

We show that the vibronic motion of a trapped ion far from the Lamb-Dicke regime can be described, under appropriate resonance conditions, by a strongly nonlinear, multiquantum Jaynes-Cummings model. In contrast to previous nonlinear or multiphoton generalizations of the Jaynes-Cummings model, it could presently be realized in experiments.

We present a system of modulation equations that approximate the focusing of the nonlinear Schrödinger equation in the presence of a small normal time dispersion (TDNLS). Since the modulation equations are much easier for analysis and for numerical simulations, they can be used to get a general picture of the TDNLS focusing. Analytical and numerical agreement between the modulation equations and the TDNLS is established.

The aim of this paper is to provide a vectorial model which can describe the dynamics of the two transverse field polarizations presented by an optical fiber laser. These dynamics are supposed to take their origin from the interaction between the propagating field and the atoms: an assumption based on the existence of a transverse distribution of dipole moments and which leads to a vectorial atomic polarization. Also, and as we have considered a frequency for each field polarization, a longitudinal dependence of the population inversion must be taken into account. A double Fourier expansion (transverse and longitudinal) of the material variables is then needed and the resulting model is analyzed using the bifurcation theory: the existence of all stationary states is fully expressed in the parameter space. The stability of these states and the system dynamic is studied in the following paper [Phys. Rev. A 52, 4243 (1995)].

In a previous paper [Phys. Rev. A 52, 4229 (1995)] a vectorial model has been derived to describe the dynamics of an optical fiber laser output. In this semiclassical theory, the time-dependent behaviors of the two field polarizations are deduced through the interaction between the light and the active atoms which supposes the presence of a vectorial atomic polarization. This paper is devoted to the analysis of the dynamics presented by such a model using the bifurcation theory. An analytical study investigates the parameter space as far as possible and numerical simulations show the presence of various types of behaviors displayed by the two output field polarizations in the domains where the steady states have lost their stability. The influence of the pump polarization is emphasized. The results are in accordance with the experimental observations.

For a two-parameter class of local potentials which support a bound state with energy ${\mathit{E}}_1$ embedded in the continuous spectrum, we determine the conditions that the potential has m wells with barriers of height greater than ${\mathit{E}}_1$. Although ${\mathit{E}}_1$≳V(∞)=0, such wells act as traps for a classical particle, with classical turning points wherever a barrier height reaches the energy of the particle. However, the parameters of the potential may easily be chosen so that there are no classical turning points, even though the potential supports a bound quantum state.

We show that higher-order corrections to the lowest-order semiclassical quantization rule vanish in the case of three known shape-invariant potentials with broken supersymmetry thereby establishing that the lowest-order formula is indeed exact for these shape-invariant potentials with broken supersymmetry.

The hyperfine interaction constants, specific-mass-shift parameters, and total energies for the 3s${\mathrm{}}^2$S and 4s${\mathrm{}}^2$S states in lithium were calculated using the multiconfiguration Hartree-Fock method. The configuration expansions were obtained with the active space method, where configuration state functions are generated by excitations from the reference configuration to an active set of orbitals. The active set was increased in a systematic way, allowing the convergence of the studied parameters to be monitored. The obtained nonrelativistic energies are close to the lowest-upper-bound estimates from Hylleraas calculations. Whereas the convergence rate of the hyperfine interaction constants with respect to the increasing basis in the Hylleraas calculations degrades appreciably for higher states in the Rydberg series, no such effect could be seen for the multiconfiguration Hartree-Fock calculations. The uncertainties of the calculated hyperfine interaction constants are estimated to be less than three parts in a thousand for both of the studied states. The value for the 3s${\mathrm{}}^2$S state is in excellent agreement with results from relativistic many-body perturbation theory calculations, but is well outside the error bars from a recent precision measurement using Stark spectroscopy.

A laser-induced resonant transition in metastable antiprotonic helium atoms has been found at a wavelength of 470.724±0.002 nm and assigned to the transition (n,l)=(37,34)→(36,33). From the time evolution of the laser resonance intensity, the decay rate of the (37,34) state was determined to be 1.17±0.09 μ${\mathrm{s}}^{\mathrm{-}1}$, about 60% larger than the theoretical radiative decay rate. The sum of the initial populations in the v=n-l-1=2 decay chain was 23±4% of the total number of metastable atoms formed.

Whether an approximate scattering state vector retains the normalized nature of its exact counterpart reflects on the quality of the approximation made. It is shown that the distorted-wave strong-potential Born state vector, employed in asymmetric electron-capture theory, is normalized (in a near-the-energy-shell approximation) to within a few percent, even at intermediate energies where capture is most likely. There is thus little need to renormalize the state, in contrast to the analogous undistorted state vector [J. Phys. B 25, 3823 (1992)], where a radical loss of normalization occurs.