Robert T. Deck

Enhancement of second-harmonic generation by coupling to long-range surface plasmons

We show theoretically that by use of a new coupling geometry the second-harmonic light generated at the surface of a thin metal film can be enhanced dramatically through a coupling of the fundamental field to a long-range surface-plasmon mode. The resulting reflected harmonic intensity is predicted to be more than 2 orders of magnitude larger than that obtainable in the standard Kretschmann or Otto geometry.

Optical bistability with the waveguide mode

We present an exact plane-wave treatment of the triple-boundary waveguide geometry for the study of optical bistability. It is found that the switching intensity required to observe the desired switching behavior is lower by at least a factor of 25 from that previously reported, thus making this geometry a prime candidate for experimental investigation. A comparison with the results of an approximate theory is also presented, showing that the approximate theory closely describes the behavior of the system as predicted by the exact theory.

Coupling between finite electromagnetic beam and long-range surface-plasmon mode

In this paper, we consider a layered structure consisting of dielectric, metal, and dielectric media and compute the fields produced in the structure by a finite width beam of incident radiation which couples to a long-range surface-plasmon mode in the metallic layer. The analysis allows for complex dielectric constants in all media and focuses on optical radiation. Curves are presented which show the profiles of the reflected field intensity for different values of the propagation length of the mode relative to the width of the incident beam. We discuss the conditions in which the field reradiated from the long-range surface mode can interfere with the specularly reflected radiation so as to produce an interference zero in the reflected profile. In these conditions our analysis allows for a determination of the separate loss coefficients of the mode associated with energy reradiation and dissipation, respectively

Surface-plasmon enhanced harmonic generation at a rough metal surface

In this paper, we compute the second harmonic radiation generated at a roughened metal surface which is describable in terms of randomly distributed height and spacing roughness variables. The roughness of the surface allows incident radiation to be coupled to a surface-plasmon mode in the metal at frequency ω that beats with the fundamental field at the same frequency to produce a 2ω field of frequency which radiates from the metal in a narrowly defined direction. Given appropriate rough surface parameters, the latter radiation can in principle serve as a well-collimated coherent source of radiation at the second harmonic frequency. We compare the collimated intensity of the harmonic produced by the roughness-induced plasmon coupling with that produced by specular reflection from the metal surface. The former intensity is predicted to exceed the latter by as much as 2 orders of magnitude.

Nuclear size corrections to the energy levels of single-electron and -muon atoms

We formulate an analytic method which accounts for the finite size of the nucleus by treating it as a boundary value problem. The method is used to obtain solutions of the Dirac equation for a central potential that is proportional to 1/r only for values of the radial coordinate greater than a given value R. Our results are applied to a non-perturbative calculation of the nuclear size corrections to the energy levels of single-electron and single-muon atoms. For values of the nuclear charge number Z greater than 40 in the case of electronic atoms, and greater than 1 in the case of muonic atoms, we find large discrepancies between our results for the atomic energy levels and those obtained from first-order relativistic perturbation theory.

Temporal pulse reshaping with surface waves

The temporal reshaping of short optical pulses reflected from a metal film under the condition of surface-wave excitation of single- and multiple-boundary surface-plasmon modes is theoretically investigated. Reflected pulse shapes are calculated through evaluation of Fourier transform integrals both by direct numerical integration and by approximate pole expansion. The latter is particularly useful for the interpretation of the simple exponential time decay of the trailing edge of the pulse. Emphasis is placed on determination of the range of parameters for which pulse reshaping may be experimentally observed. Diffraction of the incident beam is a limiting factor.

Determination of bending losses in rectangular waveguides

This paper details an accurate method for computation of bending losses in rectangular optical waveguides which we combine with perturbation theory to account for the fields in the (outer) corner regions of the guiding channel. In the case of the weakly guiding channels of interest in optical signal processing, the correction to the loss coefficient due to the corner fields is shown to be in excess of 50%.

EXCIMER STATES AND ENHANCED TWO-PHOTON ABSORPTION IN INTRAMOLECULAR CHARGE-TRANSFER CRYSTALS

Abstract We explain enhance two-photon absorption in certain centrosymmetric organic molecular crystals in which intramolecular charge transfer takes place. Specifically we suggest that charge transfer allows the interacting molecules in a unit cell to have non-zero dipole moments in the excited state of the molecules, contributing to a resonance in the two-photon absorption coefficient. Anti-parallel orientation of the molecular dipole moments in the unit cell allows for formation of excimer states and disallows the production of SHG in the same materials. We estimate the ratio of the two-photon to the one-photon absorption coefficient for some typical parameters.

All-optical combiner-splitter and gating devices based on straight waveguides

A two-mode optical combiner-splitter device is designed based on all straight waveguides that maintains the integrity of the two modes during propagation and allows for an analytic analysis. The design analysis has the potential to improve the precision of the device fabrication. The design is used in an analytic optical gate based on a nonlinear Mach-Zehnder interferometer. The design reduces the size of a previously proposed device and simplifies its analysis.

Modified theory of three-channel Kerr-type nonlinear directional coupler

We point out inconsistencies in previous analyses of multiple-channel nonlinear directional couplers based on Kerr-type media and present a modified set of coupled-mode equations for a three-channel nonlinear coupler that indicate a mode of power switching between channels with increased input power that is both qualitatively and quantitatively different from that predicted previously.