The interaction of a trapped ion with a laser beam in the strong-excitation regime is analyzed. In this regime, a variety of nonclassical states of motion can be prepared either by using laser pulses of well defined area, or by an adiabatic passage scheme based on the variation of the laser frequency. We show how these states can be used to investigate fundamental properties of quantum mechanics. We also study possible applications of this system to build an ion interferometer. © 1996 The American Physical Society.

We discuss the mechanisms of multielectron dissociative ionization of diatomic molecules in intense laser fields. We show that during dissociation of molecular ions the nuclei pass through a critical range of internuclear distances where ionization is enhanced by several orders of magnitude for several successive charge states of the molecule. The critical range of internuclear distances depends only weakly on the laser frequency, laser intensity, and the charge state. Both numerical and analytical models are developed, and the effect of enhanced ionization on the kinetic energy and angular distributions of charged fragments is discussed. © 1996 The American Physical Society.

The resonant multiphoton-ionization (MPI) processes in a strongly coupled atomic system have been investigated theoretically and experimentally using atomic hydrogen as a test medium. The characteristics are described with a parameter NL: the product of atom density and interaction length. The MPI characteristics exhibit a single-atom behavior revealing an Autler-Townes doublet in the low-NL region. In the high-NL region, the Autler-Townes doublet is suppressed to almost zero. This phenomenon is shown to be due to destructive interference between the excitation channels to the strongly coupled upper states. It is also shown that a narrow Doppler-free MPI peak appears at the split center of the Autler-Townes doublet in the high-NL region as a consequence of the strong coupling and the propagation effect. © 1996 The American Physical Society.

The technique of stimulated Raman adiabatic passage (STIRAP) has become an established procedure for producing complete population inversion in atoms or molecules via application of Stokes and pump pulses in a counterintuitive sequence. Previously we reported on numerical and analytical investigations showing some of the additional and important phenomena that arise when some of the levels involved have nonzero angular momentum, the field polarization directions have no simplifying symmetries, and Zeeman splitting lifts the magnetic sublevel degeneracy. Here we verify our theoretical findings using the metastable neon system: ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_0$${\mathrm{?}}^3$${\mathit{P}}_1$${\mathrm{?}}^3$${\mathit{P}}_2$ with the corresponding angular momentum sequence J=0?J=1?J=2. In particular, we demonstrate that it is possible to transfer all population from the single initial state to any single selectable final magnetic sublevel M. Selectivity can be achieved either by choosing special laser polarization angles or, for fixed polarizations, by tuning the two lasers into two-photon resonance between the initial and desired final state. The complete control of magnetic sublevel population enabled by this procedure extends the customary experimental methods for producing oriented or aligned beams of atoms. In addition, we demonstrate very clearly the previous prediction that population transfer may fail for certain sets of parameters (detunings, Rabi frequencies, and polarization angles). © 1996 The American Physical Society.

We present results of calculations of rates for ionization of ${\mathrm{H}}_2^{+}$ by up to six photons in lowest nonvanishing order of perturbation theory, for a fixed internuclear separation of 2 a.u. There are numerous intermediate state resonances, which we identify by united-atom-limit quantum numbers. We also report on ionization rates at nonperturbative intensities at the wavelength 228 nm, calculated by resumming the Rayleigh-Schrödinger perturbation series for the ac quasienergy; we compare our results with those of previous calculations. © 1996 The American Physical Society.

The formation of ${\mathrm{Ca}}^{+}$ ions is measured in an effusive Ca beam by exciting through either the 4s4${\mathit{p}}^1$${\mathit{P}}_1$ or the 4s5${\mathit{p}}^1$${\mathit{P}}_1$ state to highly excited Ca*(4${\mathit{snd}}^1$${\mathit{D}}_2$) Rydberg states. In agreement with previous work by McLaughlin and Duquette [Phys. Rev. Lett. 72, 1176 (1994)], when the Rydberg states are accessed through the 4s5${\mathit{p}}^1$${\mathit{P}}_1$ state, we detect a large increase in ${\mathrm{Ca}}^{+}$ ions for n=25, compared to other high-n Rydberg states. It had been reported (Fabrikant [Phys. Rev. A 48, R3411 (1993)]; McLaughlin and Duquette) that ‘‘ground-state–Rydberg-state’’ collisions cause this large increase in ion production and that the result provides a precise value of the electron affinity of Ca through the binding energy of the Rydberg electron. However, a variation of the original experiment in which the same Rydberg states are accessed through the 4s4${\mathit{p}}^1$${\mathit{P}}_1$ level instead of the 4s5${\mathit{p}}^1$${\mathit{P}}_1$ level shows no enhancement of ions for any particular Rydberg level. With a three-laser experiment we show that the enhanced ionization effect for the 25d state is due to the 3${\mathit{d}}_{3/2}$9${\mathit{f}}_{5/2}$, ${\mathit{J}}^{\mathrm{\pi }}$=$2^{\mathrm{-}}$ autoionizing resonance, which is coincidentally accessed from the Ca(4s25${\mathit{d}}^1$${\mathit{D}}_2$) state by the 808-nm photon involved in the original experiment by McLaughlin and Duquette. The existence of this resonance close to the experimentally observed energy is also established by R-matrix calculations. © 1996 The American Physical Society.

It is shown that a three-level atom in the Λ configuration with arbitrary detunings can be exactly reduced to a two-level system with an effective Raman coupling, which depends nonlinearly on the intensity of the two radiation fields. This is done by exactly evaluating the unitary transformation introduced by Alexanian and Bose [Phys. Rev. A 52, 2218 (1995)] for a three-level atom coupled to two modes of the radiation field. We obtain an exact transformed Hamiltonian in which one of the three levels is decoupled for all values of the detunings. In particular, our result is then valid for any ratios of the coupling constants to detunings, even for zero detuning, in contrast to earlier work which requires that these ratios be small. We find the the eigenvalues of the exact transformed Hamiltonian and study its population dynamics. © 1996 The American Physical Society.

Particle rotation resulting from the absorption of light carrying angular momentum has been measured. When absorbing CuO particles (1-5μm) were trapped in a focused ‘‘donut’’ laser beam, they rotated, due to the helical phase structure of the beam. Changing the polarization of the light from plane to circular caused the rotation frequency to increase or decrease, depending on the sense of the polarization with respect to the helicity of the beam. Rotation frequencies were obtained by Fourier analysis of amplitude fluctuations in the backscattered light from the particles. © 1996 The American Physical Society.

We present measurements of the transverse and longitudinal coherence lengths of the fourth harmonic of a 1053-nm, 2.5-ps laser generated during high-intensity (up to ${10}^{19}$ W ${\mathrm{cm}}^{\mathrm{-}2}$) interactions with a solid target. Coherence lengths were measured by use of a Young’s double-slit interferometer. The effective source size, as defined by the Van Cittert–Zernicke theorem, was found to be 10–12 μm, and the coherence time was observed to be in the range 0.02–0.4 ps. © 1996 The American Physical Society.

We examine a model of a driven two-level system with injected coherent atoms. We find a set of lasing phase diagrams for the resonant excitations. We show that the laser field in the system is related to the initial preparation of atoms, and that when the degree of this coherence is changed, the system exhibits bistability in the inversionless region. We also discuss the crucial role of atomic coherence in achieving lasing action. © 1996 The American Physical Society.

Transverse pattern formation in both degenerate optical parametric oscillation and degenerate four-wave mixing is considered both theoretically and numerically. In the limit of small signal detuning both systems are shown to be described by the real Swift-Hohenberg equation. Contrarily, for small signal and large pump detunings the Swift-Hohenberg equation is modified differently in both systems, by the appearance of additional nonlinear terms, which signal the existence of nonlinear resonances that are theoretically studied through the derivation of the amplitude equation for the roll pattern in both systems. Numerical analysis supports the theoretical predictions. © 1996 The American Physical Society.

We discuss a laser with N three-level atoms resonantly and cooperatively interacting with two cavity modes. Its intensity is proportional to ${\mathit{N}}^2$, the linewidth scales as 1/${\mathit{N}}^2$, and the output intensity fluctuations display up to 100% squeezing at low frequencies. We show that quantum fluctuations of the pump do not deteriorate the squeezing significantly. We also find that the fluctuation properties of the ‘‘passive’’ cavity mode which serves to collectively relax the atoms to the ground state are similar to those of the active mode. Finally we take into account spontaneous emission. Within a certain range of frequencies good squeezing can still be found. © 1996 The American Physical Society.

We study analytically the intensity phase coherence in a three-mode Fabry-Pérot laser. We consider in detail the case of a central mode with maximum gain and two side modes with smaller but equal gains. This laser is characterized by three relaxation oscillation frequencies ${\mathrm{\Omega }}_{\mathit{R}}^{\mathrm{″}}$≳${\mathrm{\Omega }}_{\mathit{L}1}^{\mathrm{″}}$≳${\mathrm{\Omega }}_{\mathit{L}2}^{\mathrm{″}}$. In the framework of a linearized theory, the laser dynamics is, respectively, inphased and perfectly antiphased at ${\mathrm{\Omega }}_{\mathit{R}}^{\mathrm{″}}$ and ${\mathrm{\Omega }}_{\mathit{L}2}^{\mathrm{″}}$, irrespective of the modal gains. At ${\mathrm{\Omega }}_{\mathit{L}1}^{\mathrm{″}}$ the antiphase is only partial if the side mode gains are smaller than the central mode gain. Analytic gain- and pump-dependent relations between the three frequencies and between the heights of the peaks in the power spectra at these frequencies are established. We also derive universal relations between the peaks of the power spectra of the modal and the total intensities at the same frequencies that do not involve any parameter at all. © 1996 The American Physical Society.

Due to the transverse device symmetry, the polarization properties of the light generated by surface-emitting semiconductor lasers will be strongly influenced by residual anisotropies. We describe the polarization dynamics of these lasers on the basis of a theoretical model founded on the coexistence of two different electron-hole recombination transitions, which give rise to circularly polarized fields with opposite helicities; the carrier densities available for these two transitions are coupled via spin-mixing processes. The residual cavity anisotropies are introduced in the model by means of the boundary conditions imposed to the counterpropagating fields: anisotropies which are symmetric and antisymmetric under time reversal will generate different boundary conditions. We include in the equations the effects of material strain, which causes symmetric linear phase and amplitude anisotropies, and of an externally applied magnetic field, which induces antisymmetric circular phase and amplitude anisotropies via the Faraday effect. This theoretical framework allows us to explain, with realistic values of the system parameters, some of the polarization behaviors exhibited by surface-emitting semiconductor lasers, namely, bistability and switching between orthogonal linearly polarized fields and magnetically induced ellipticity. © 1996 The American Physical Society.

Using the Green-function approach to the problem of quantization of the phenomenological Maxwell theory, the propagation of quantized radiation through dispersive and absorptive multilayer dielectric plates is studied. Input-output relations are derived, with special emphasis on the determination of the quantum noise generators associated with the absorption of radiation inside the dielectric matter. The input-output relations are used to express arbitrary correlation functions of the outgoing field in terms of correlation functions of the incoming field and those of the noise generators. To illustrate the theory, photons at dielectric tunneling barriers are considered. It is shown that inclusion in the calculations of losses in the photonic band gaps may substantially change the barrier traversal times. © 1996 The American Physical Society.

A simple and efficient method for direct sampling of the density matrix of a signal mode in optical homodyne tomography is developed. The method is based on approximate, quasianalytical techniques of Fourier transform and yields the density matrix in an arbitrary field-strength basis. It is also suitable for direct sampling of density matrices of matter systems in generalized position or momentum bases. © 1996 The American Physical Society.

A scheme for preparing vibrational SU(2) states of motion in a two-dimensional ion trap is described. These anticorrelated two-mode states are formally equivalent to the output photon states of a lossless SU(2) interferometer with number-state inputs. Nontrivial statistics such as the binomial distribution and the discrete ‘‘arcsine’’ distribution can be generated in the vibrational states of trapped ions, and detected by measuring the population inversion of the ion driven by a laser field along a specific direction. © 1996 The American Physical Society.

We present a perturbative derivation of the fluorescence spectrum for a three-level atom driven by a classical radiation field. The energies of the three atomic levels are equal to ħ${\mathrm{\omega }}_{\mathrm{i}}$ (i=1, 2, and 3) with ${\mathrm{\omega }}_3$≳${\mathrm{\omega }}_2$≳${\mathrm{\omega }}_1$ and ${\mathrm{\omega }}_{32}$≫${\mathrm{\omega }}_{21}$ (${\mathrm{\omega }}_{\mathit{ij}}$=${\mathrm{\omega }}_{\mathit{i}}$-${\mathrm{\omega }}_{\mathit{j}}$). The radiation field, having a frequency Ω≳${\mathrm{\omega }}_{31}$, can be considered to drive the 2-3 transition only. Spontaneous emission from the ground state, via a normally counter-rotating atom-vacuum interaction term in the Hamiltonian, conserves energy when a photon is subsequently absorbed from the laser field. The spectrum is explained in terms of a Raman process, and in terms of an interaction between the laser field and the coupled atom-vacuum field system. Connection is made with a dressed-atom description of the problem. © 1996 The American Physical Society.

The optimum detection operators are derived for several linearly independent signal sets. The quantum minimax strategy is applied to the M-ary coherent state signals such as binary phase shift, ternary symmetric, ternary phase shift, and quadrature phase shift. It is shown that the detection process induces a kind of quantum interference between signal quantum states and measurement states. © 1996 The American Physical Society.

Phase-modulation effects in self-diffraction with two pump beams incident on a nonlinear medium were studied theoretically and experimentally. Based on a two-level model and considering the influence of the phase modulation on the phase matching, expressions describing the first-order and second-order scattered intensities were derived. The influences of phase modulation on the pump-intensity dependence and the sample-concentration dependence of the scattered intensities were discussed via numerical calculations. Experiments were performed with tetrahydrofuran solution of 1,4-diethinyl benzene to demonstrate the theoretical results. Some interesting results predicted by the theory, such as the fact that the scattered intensities of the sample with lower concentration can be larger than that with higher concentration at suitable high intensity of the pump, have been observed. © 1996 The American Physical Society.