Ralph G. Devoe

Observation of superradiant and subradiant spontaneous emission of two trapped ions

Summary form only given. We report a laboratory realization of the gedanken experiment that Dicke used to introduce superradiance. Two Ba/sup +/ ions are laser-cooled and crystallized in a microscopic Paul trap so that they come to rest 1.5 microns from each other. This is about 3 wavelengths of the 493 nm light used to laser cool the transition. Micromotion and residual thermal motion are low so that they are essentially stationary relative to 493 nm light.

Design of optimized photorefractive polymers: A novel class of chromophores

It is demonstrated that the microscopic mechanism of the photorefractive (PR) effect in organic composites with low glass transition temperatures involves the formation of refractive index gratings through a space‐charge field‐modulated Kerr effect. A tensorial formulation of the macroscopic aspects of the PR Kerr effect and its microscopic interpretation is presented. The second‐order dipole orientation term containing the anisotropy of the first‐order optical polarizability α(−ω;ω) is shown to yield the dominant contribution to the Kerr susceptibility χ(3)(−ω;ω,0,0). A class of special chromophores having negligible second‐order polarizabilities β(−ω;ω,0) and large dipole moments μ has been identified in order to optimize this term. These chromophores are not subject to the efficiency‐transparency tradeoff typically encountered with second‐order nonlinear optical (NLO) chromophores, providing highly transparent materials with large PR Kerr response. Contrary to previous approaches in this field, the bes...

Holographic data storage in photorefractive polymers

Summary form only given. Holographic data storage offers the potential of extremely high storage densities and high data transfer rates. The search for read-write storage systems based on the photorefractive effect has been limited by the availability of materials that combine good optical quality, high sensitivity and index modulation, long dark lifetime and/or viable fixing mechanisms. Organic photorefractive materials have been the subject of great interest during the past several years, but experiments involving practical data storage schemes have not been reported. We describe the results of recent investigations into high-density digital data storage in photorefractive polymer materials.

Optical-fiber media for squeezed-state generation

The Kerr nonlinearity characteristic of optical fibers produces squeezed states of light by a mechanism that differs from conventional four-wave mixing. The noise sources characteristic of such a medium also have a unique character. We present a unified picture of these interactions for both traveling-wave and cavity geometries. Results of experiments on squeezing in optical fibers and fiber ring resonators are discussed and compared with the theory.

A novel sensitized photochromic organic glass for holographic optical storage

A new class of photochromic glasses for use in irreversible holographic optical storage applications is described. The recording mechanism involves a triplet‐sensitized photoreaction of an organic chromophore. The materials are isotropic and red‐sensitive, and exhibit high diffraction efficiencies and long hologram lifetimes. The wavelength sensitivity can be adjusted by the choice of sensitizer; C60, sensitive in the red, is described here. Single digital data page recording and error‐free readout are demonstrated at a density of 0.5 Mb/cm2; multiplexing in a 150‐μm‐thick sample is also demonstrated.

Role of laser damping in trapped ion crystals

Publisher Summary Cooling by laser radiation pressure is essential to reach the milliKelvin temperatures at which crystallization can occur. Cooling rates depend on array size and on the position of the ion in the array. Cooling rates can reverse sign so that heating occurs below resonance and cooling occurs above resonance. Cooling rates depend sensitively on trap parameters—for example, trap voltage and frequency. The inhibition of laser cooling is caused by Doppler shifts arising from radio frequency micromotion. Ions in an rf quadrupole trap undergo micromotion oscillations about their equilibrium position at the frequency of the rf trap voltage Ω. In ion arrays, substantial micromotion is always present to balance the mutual Coulomb repulsion of the ions. Micromotion amplitudes are comparable to the wavelength of the cooling radiation and strong Doppler shifts result. Micromotion Doppler shifts can reduce or even reverse the sign of laser cooling in ion crystals relative to single ions. This chapter describes a few experiments that demonstrate spectral broadening and the inhibition of laser cooling by micromotion.

The Order-Chaos Transition of Two Trapped Ions

Publisher Summary Trapped particles can describe two very different kinds of motion: (1) small oscillations about equilibrium points in an ordered array and (2) disordered, apparently random motion. Transitions between those two types of motion could be induced by varying the trapping potential. This chapter describes order–chaos transitions in a deterministic dynamical system. Analysis of the extended trajectories shows the typical characteristics of deterministic chaos: the Fourier spectrum is continuous even though the system has only six degrees of freedom, and the largest Lyapunov exponent goes from zero in the quasiperiodic state to a positive value in the chaotic state. The chapter describes an experiment that shows the transition between ordered and chaotic motion for two trapped, laser-cooled barium ions. The ions were detected by scattered laser light at 493 nm together with a second laser at 650 nm that also cooled the ions. In the chaotic state, the fluorescence count rate drops dramatically due to the large Doppler effect.

Ultrahigh-finesse optical cavities

As the finesse of a Fabry-Perot optical cavity increases to about 20,000, the fringe width (approximately 10 kHz for a 50-cm cavity) is sufficiently narrow for transverse-mode splittings to be resolved by using a highly stabilized ring dye laser. A perturbative theory interprets this effect as a slight deviation of the cavity from cylindrical symmetry, the magnitude of the asymmetry being at the level of a few tenths of a nanometer. The understanding of these splittings will permit accurate optical frequency measurements by the recently proposed optical-radio-frequency divider.

Precision measurements of the lifetime of a single trapped ion with a nonlinear electro-optic switch

A time-correlated single-photon counting method is used to measure the spontaneous emission lifetime of a single trapped barium ion, yielding a standard deviation of 0.5% for 8 min of integration time. The statistical power of this one-atom technique is comparable with that of other methods that use a macroscopic sample, but the technique has potentially lower systematic errors. The method depends on the use of an electro-optic phase modulator as an Nth-order nonlinear switch, which improves the response time by a factor of N and the on–off ratio by the Nth power.

Magic Angle Line Narrowing in Optical Spectroscopy

Spin decoupling and line narrowing are observed for the first time in an optical transition, 3H4 ↔ 1D2 of Pr3+. in LaF3 at 2°K, using optical FID. The 19F nuclei, when irradiated by an appropriate rf field, undergo forced precession about an effective field at the magic angle in the rotating frame. The fluctuating 19F–19F dipolar interaction is thereby quenched and the optical linewidth drops from ~10 to ~2 kHz, as predicted in a theory of spin diffusion.