Jennifer M. Reed

Beam deflection measurement of bound-electronic and rotational nonlinear refraction in molecular gases.

A polarization-resolved beam deflection technique is used to separate the bound-electronic and molecular rotational components of nonlinear refractive transients of molecular gases. Coherent rotational revivals from N(2), O(2), and two isotopologues of carbon disulfide (CS(2)), are identified in gaseous mixtures. Dephasing rates, rotational and centrifugal distortion constants of each species are measured. Polarization at the magic angle allows unambiguous measurement of the bound-electronic nonlinear refractive index of air and second hyperpolarizability of CS(2). Agreement between gas and liquid phase second hyperpolarizability measurements is found using the Lorentz-Lorenz local field correction.

Shape of Fano resonance line spectra calculated for silver nanorods.

Using theoretical tools, we numerically demonstrated Fano line shapes in the scattering spectra of silver rods resulting from different mechanisms. One of the Fano line shapes is due to the coupling of an in-plane quadrupole and a dipole mode in a single rod. Two nodes were observed at the resonance wavelength, each of which is located at a quarter of the rod length from the two ends. The Fano resonance is strengthened when the silver rod is cut at the two nodal positions. The second mechanism that gives rise to a new Fano resonance peak occurs when the symmetry of the rod is broken and is a result of the asymmetric coupling between the two excited dipoles.

Numerical Study of Mode Excitation in a Partially Illuminated Silver Rod

Using electrodynamics theory, we numerically demonstrated that when the incident light polarization direction is parallel to a silver rod axis, the modes that are forbidden in a fully illuminated silver rod can be excited when the rod is partially illuminated. The modes are excited due to the symmetry breaking of the rod when it is partially illuminated. They are characterized by the even number of nodes in the excited surface plasmons and quadrupole pattern of the scattered light in the space. These modes are different from the allowed modes in a fully illuminated rod, which shows an odd number of nodes in the excited surface plasmons and a dipole pattern of the scattered light. The conclusion was further supported by the calculation results when the illuminated spot was moved from the rod end to its center and when the illuminated length was varied. We also demonstrated dark modes when the incident light polarization is perpendicular to the rod axis. Contrary to the hypothesis that a dark mode will be an efficient waveguide mode, the dark mode shows very poor waveguide applications when the incident polarization is perpendicular to the rod axis.

Analysis of beam deflection measurements in the presence of linear absorption

We develop a series of analytical approximations allowing for rapid extraction of the nonlinear parameters from beam deflection measurements. We then apply these approximations to the analysis of cadmium silicon phosphide and compare the results against previously published parameter extraction methods and find good agreement for typical experimental conditions.

Subwavelength light confinement and propagation: A numerical study of a two-layer silver film with perforated holes

Confinement and propagation of light under the diffraction limit is a substantial challenge for the development of waveguides as components in subwavelength optical devices. Light confinement and propagation at optical frequencies in a two-layer silver film with a periodic array of holes is investigated in a numerical study using the discrete dipole approximation method. Extraordinary subwavelength confinement and propagation of light can be obtained along an extremely subwavelength cross section of a region as small as 10 × 20 nm2 at a distance of over 10 μm. This study provides rational design of waveguides under subwavelength dimensions.

Effect of surrounding medium on the optical properties of a two layer silver film

The effect of surrounding medium on the optical properties of a two layer silver film are investigated using an analytical model. We varied the media before the first layer, between the two layers, and after the second layer. We find that the optical properties of the film is dominantly determined by the medium between the two layers. The resonance wavelength red shifts when the medium between the two layers is changed from vacuum to water and then glass. The media before the first layer and after the second layer have little effect on the spectra of the film when the thicknesses of the layers are larger than 40 nm.