Spontaneous Raman scattering is investigated theoretically by considering a completely classical description of the process that takes place within the mirrors of a microscopic Fabry-Pérot cavity. This analysis is based on the image method within the framework of the classical theory of light scattering. In order to account for the finite reflectivities of the mirrors, the result for the scattered field is presently determined analytically only in the limit of low finesse of the optical cavity. This leads to a general expression for the cross section of the Stokes transition that explains the results recently reported in the literature [F. De Martini, M. Marrocco, C. Pastina, and F. Viti, Phys. Rev. A 53, 471 (1996)]. Therefore, in the limit of low finesse of the cavity, one must accept that this effect has a fundamentally classical nature. © 1996 The American Physical Society.

We discuss the influence of the laser pulse turn-on on the radiation spectrum emitted by an atom strongly driven by an intense laser field. For this purpose we use the results obtained from the direct numerical solution of the time-dependent Schrödinger equation and from a Floquet analysis of the wave function. We observe a strong dependence of the intensities of the harmonics and of the hyper-Raman lines on the duration of the turn-on, with differences that can reach several orders of magnitude. This dependence can be explained in terms of population transfers between Floquet states at avoided crossings. We support our analysis with numerical simulations for a two-level system and also with the help of a more realistic model, the one-dimensional soft Coulomb potential, obtaining similar results. ©1996 The American Physical Society.

In several recent experiments, isotropic lasing action was observed in paints that contain rhodamine 640 dye molecules in methanol solution as gain media and titania particles as optical scatterers. These so-called paint-on laser systems are extraordinary because they are highly disordered systems. The microscopic mechanism for laser activity and the coherence properties of light emission in this multiple-light-scattering medium have not yet been elucidated. In this paper we derive the emission intensity properties of a model dye system with excited singlet and triplet electronic energy levels, which is immersed in a multiple-scattering medium with transport mean free path l*. Using physically reasonable estimates for the absorption and emission cross section for the singlet and triplet manifolds, and the singlet-triplet intersystem crossing rate, we solve the nonlinear laser rate equations for the dye molecules. This leads to a diffusion equation for the light intensity in the medium with a nonlinear intensity-dependent gain coefficient. Using this model we are able to account for nearly all of the experimentally observed properties of laser paint reported so far when l*≫${\lambda }_0$, the emission wavelength. This includes the dependence of the peak intensity of amplified emission on the mean free path l*, the dye concentration ρ, and the pump intensity characteristics. Our model recaptures the collapse of the emission linewidth at a specific threshold pump intensity and describes how this threshold intensity varies with l*. In addition, our model predicts a dramatic increase in the peak intensity and a further lowering of the lasing threshold for the strong scattering limit l*→${\lambda }_0$. This suggests a striking enhancement of the characteristics of laser paint near the photon localization threshold in a disordered medium. © 1996 The American Physical Society.

We report the experimental observation of steady-state electromagnetically induced transparency and sub-Doppler linewidth in a Doppler-broadened Λ-type Rb atomic system formed on the ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ ${\mathit{D}}_2$ transitions. The Λ system is coupled on one transition by a strong laser and probed on the other transition by a weak laser. The observed sub-Doppler linewidth decreases with the increasing detuning of the strong-coupling laser from the atomic transition frequency and is in good agreement with the theoretical calculations of G. Vemuri, G. S. Agarwal, and B. D. N. Rao [Phys. Rev. A 53, 2842 (1996)]. © 1996 The American Physical Society.

It is shown, under mild assumptions, that classical degrees of freedom dynamically coupled to quantum ones do not inherit their quantum fluctuations. It is further shown that if the assumptions are strengthened by imposing the existence of a canonical structure, only purely classical or purely quantum dynamics is allowed. © 1996 The American Physical Society.

The static dipole and quadrupole polarizabilities of ${\mathrm{F}}^{\mathrm{-}}$, ${\mathrm{Si}}^{\mathrm{-}}$, and ${\mathrm{Cl}}^{\mathrm{-}}$ are calculated using many-body perturbation theory and coupled-cluster methods. The results for the dipole polarizabilities, obtained using the double substitution coupled-cluster (CCD) plus single and triple CCD [CCD+ST(CCD)] scheme, the highest level of approximation, are 15.5, 145.4, and 36.4 a.u. for ${\mathrm{F}}^{\mathrm{-}}$, ${\mathrm{Si}}^{\mathrm{-}}$, and ${\mathrm{Cl}}^{\mathrm{-}}$, respectively. For the quadrupole polarizabilities, we obtained 1.98×${10}^2$, 2.48×${10}^3$, and 3.92×${10}^2$ a.u., respectively. © 1996 The American Physical Society.

Coincidence measurements of the angular distributions of ${\mathrm{O}}^{+}$ dissociated from ${\mathrm{O}}_2$${\mathrm{}}^{2+}$ produced by electron impact on ${\mathrm{O}}_2$ have been made. With an incident electron energy of 55 eV, 2.6-, 3.7-, 4.5-, and 5.8-eV ${\mathrm{O}}^{+}$ ions were detected separately using the time-of-flight and coincidence method at selected angles between 40° and 140° in 10° steps. The results show two flat, isotropic and two anisotropic angular distributions and attempts have been made to interpret these symmetries and to identify the sources of the ions. © 1996 The American Physical Society.

A relation is proposed to compare data for the ratio R of cross sections for double ionization (or ionization excitation) (${\mathrm{\sigma }}^2$) to that for single ionization (${\mathrm{\sigma }}^1$) caused by charged particles (Z), photoannihilation (PE), and Compton (C) scattering. The relation is ${\mathit{R}}_{\mathit{Z}}$(ε)=${\mathit{f}}_{\mathit{Z},\mathit{d}}$(ε)${\mathit{R}}_{\mathrm{PE}}$+[1-${\mathit{f}}_{\mathit{Z},\mathit{d}}$(ε)]${\mathit{R}}_{\mathit{C}}$( ε). Here, R(ε)=(d${\mathrm{\sigma }}^2$/dε)/(d${\mathrm{\sigma }}^1$/dε), R=${\mathrm{\sigma }}^2$/${\mathrm{\sigma }}^1$, and ${\mathit{R}}_{\mathit{C}}$(ε) is the ratio of cross sections for Compton scattering; ε is the energy transferred to the system by the projectile; and ${\mathit{f}}_{\mathit{Z},\mathit{d}}$(ε) is the dipole fraction of the energy distribution ${\mathrm{\rho }}_{\mathit{Z}}$(ε)=(d${\mathrm{\sigma }}_{\mathit{Z}}^1$/dε)/${\mathrm{\sigma }}_{\mathit{Z}}^1$ for single ionization. We have evaluated ${\mathit{f}}_{\mathit{Z},\mathit{d}}$(ε) so that only ratios of cross sections at high energies need be observed experimentally to test this relation. © 1996 The American Physical Society.

The electron-impact detachment from the ${\mathrm{H}}^{\mathrm{-}}$ and ${\mathrm{O}}^{\mathrm{-}}$ negative ions is calculated in lowest-order distorted-wave theory. The cross sections are found to be quite sensitive to the choice of polarization potential. Reasonable agreement between the distorted-wave theory and recent ion storage ring experiments for both ${\mathrm{H}}^{\mathrm{-}}$ and ${\mathrm{O}}^{\mathrm{-}}$ is obtained. © 1996 The American Physical Society.

Photoelectron spectra obtained from (CsX${)}_3$${\mathrm{Cs}}^{\mathrm{-}}$ (X=Cl,Br,I) cluster anions are strongly dependent on the temperature of the laser vaporization source in which they were produced. Spectral features that were present in clusters emerging from the source at room temperature disappear when the source is cooled to low temperature. This effect is consistent with spontaneous thermal isomerization in the isolated clusters, a precursor to the melting transition in bulk materials. © 1996 The American Physical Society.

We show how the Landau-Dykhne formula for the high-order harmonic generation can be generalized in order to account for the simultaneous interaction of photoelectrons with the laser field and the binding potential of the parent ions. Numerical illustrations indicate a significant dependence of the phase of the probability current on this interaction. © 1996 The American Physical Society.

We show that the dimension of the density matrix in Fock representation is equal to the number of phases needed for accurate state reconstruction in optical homodyne tomography. We also derive a simple method for estimating the errors if the actual dimension is larger than the number of phases. © 1996 The American Physical Society.

Muriel [Phys. Rev. A 50, 4286 (1994)] recently obtained an exact solution for the driven two-level atom without relaxation by means of complicated projection operator methods. Here we obtain his result in a much more concise way by using the Dyson expansion. ©1996 The American Physical Society.

Coherent-state expectation values of Fourier-phase-operator products (of arbitrary order) are shown to exhibit polar factorization, and to be identical for the Susskind-Glogower and the Pegg-Barnett quantum phase operators. Concurrently, it follows that q deformation only directly affects the radial part (the Higgs modes) and not the phase part (the Nambu-Goldstone modes) of these expectation values. © 1996 The American Physical Society.

We show that driven Λ-type atoms in a cell under conditions of electromagnetically induced transparency squeeze the phase noise of a traveling-wave input field in a broad spectral region. The maximum squeezing is about 41% below the shot-noise level. © 1996 The American Physical Society.

In a recent experiment Zhu and Lin [Phys. Rev. A 53, 1767 (1996)] reported gain linewidths, in a coherently pumped atomic system, which were much less than the Doppler width. We show that this observation is easily explained in terms of our work [Phys. Rev. A 53, 2842 (1996)], which is generalized to correspond to the experimental situation by inclusion of incoherent pumping, and pump and probe laser linewidths. ©1996 The American Physical Society.

Rotation-torsion energy levels of acetaldehyde calculated from a spectroscopic Hamiltonian obtained from the fit of high-resolution microwave and far-infrared spectra, exhibit anomalously large splittings for some asymmetry doublets. It is shown that these anomalies are caused by chaos-enhanced quantum dynamical tunneling between classically disconnected regions of the phase space. A major consequence of this phenomenon is the magnification of intramolecular energy-transfer processes.

We investigated the bound-state spectrum of a particle with spin $F>~\frac{1}{2}$ in the magnetic field of a thin current-carrying wire. We prove the existence of infinitely many bound states for any $F$. The bound-state energies closely follow a Coulomb-like behavior with an effective angular momentum ${\ell }^{*}$, suggesting a high adiabaticity of the system. Numerical results ($F=\frac{1}{2}, \dots , 3$) are well approximated by a single simple formula for the quantum defect, which is more accurate than the approximations given in the literature. We find a qualitative disagreement with the result obtained by adiabatic approximation.

A proposal is made for obtaining a mesoscopic realization of the Greenberger-Horne-Zeilinger (GHZ) "all or nothing" contradiction between quantum mechanics and local realism in the context of cavity QED. The proposed experiment involves three separated micromaser cavities, each initially prepared in a coherent state, which are then entangled by dispersive atom-field interactions followed by selective ionization of a single atom that has passed through all three cavities. The cavities are then probed individually by single atoms manipulated to obtain a measurement of the parity of the cavity fields. Using an isomorphism between coherent-state cavity fields and a spin-½ system, we show how this experiment gives rise to violations of local realism in the manner of GHZ.