Steven M. Blair

Localization of Near-Field Resonances in Bowtie Antennae: Influence of Adhesion Layers

The near-field resonances of gold bowtie antennae are numerically modeled. Besides the short-range surface plasmon polariton (SR-SPP) mode along the main axis of the structure, a coupled SPP mode is also found in the gap region (G-SPP). The influence of adhesion layers is considered, which depends on the refractive index and the absorption of the adhesion material and whether it is continuous or etched. A high refractive index causes the peak of the SR-SPP to red-shift. High absorption quenches the intensity of the SR-SPP. The magnitude of influence depends on the overlap of the adhesion layer with the SR-SPP and G-SPP modes. The near-field resonance of the SPP mode on the top surface is also considered. An etched metal adhesion layer changes the near-field localization in the gap and causes the enhancement peaks at different heights within the gap to red-shift from top to bottom. A simple optimization method for the near-field localization by the combination of different top and bottom layers is demonstrated.

Selective, high-optrode-count, artifact-free stimulation with infrared light via intrafascicular Utah Slanted Optrode Arrays

Here we present the first use of intraneural and intrafascicular infrared neural stimulation (INS) with early-generation Utah Slanted Optrode Arrays (USOAs) to produce highly selective, artifact-free stimulation of peripheral nerves. USOAs utilize technology previously developed for Utah Slanted Electrode Arrays, and contain 100 silicon optrodes of 0.5 to 1.5 mm length, spaced 400 μm apart in a 10 x 10 grid. The optrodes penetrate into the nerve and closely abut nerve fibers, thus providing multiple, independent, focal sites of stimulation. We first demonstrated that intraneural (but extrafascicular) infrared (IR) stimulation of cat sciatic nerve with conventional optical fibers coupled to a Lockheed Martin Aculight Capella laser produced stronger and more selective neural and muscle compound action potentials (CAPs) than did extraneural INS. We next tested INS through individual USOA optrodes (e.g., wavelength 1873 nm, 5- ms stimulus pulse, < 1 mJ at optrode tip). In contrast to extraneural INS, intrafascicular INS evoked relatively strong and highly selective, optrode-specific responses. Further, there were no observable stimulus artifacts, thereby allowing adjacent electrical recordings. These initial results indicate that intrafascicular INS via USOAs may provide a more efficient, more selective, high-optrode-count means of activating axons, plus greater access to interior nerve fibers.