High-frequency measurement of concentration in an isothermal methane-air gas mixture using spontaneous Raman spectroscopy.

A high-frequency (1.5 kHz) spontaneous Raman spectroscopy measurement technique is developed and applied to measure external fluctuations generated in the local concentration of an isothermal binary gas mixture of methane and air. Raman excitation is provided by a high-frequency laser at 527 nm in dual-pulsed mode.

Gas-phase Raman spectroscopy of non-reacting flows: comparison between free-space and cavity-based spontaneous Raman emission.

We report on a comparison of free-space and cavity-enhanced Raman spectroscopy for gas-phase measurements of nitrogen and oxygen in ambient air. Real-time analysis capabilities and continuous Raman signals with low power diodes make the technique non-invasive, affordable, compact, and applicable for usage in non-reacting flows. We derive a comprehensive model for estimation of photon emission for both free-space and cavity-based signals and discuss trade-offs in how to organize the cavity geometry for maximum gain relative to free space.

The Dependence of CNT Aerogel Synthesis on Sulfur-driven Catalyst Nucleation Processes and a Critical Catalyst Particle Mass Concentration.

The floating catalyst chemical vapor deposition (FC-CVD) process permits macro-scale assembly of nanoscale materials, enabling continuous production of carbon nanotube (CNT) aerogels. Despite the intensive research in the field, fundamental uncertainties remain regarding how catalyst particle dynamics within the system influence the CNT aerogel formation, thus limiting effective scale-up. While aerogel formation in FC-CVD reactors requires a catalyst (typically iron, Fe) and a promotor (typically sulfur, S), their synergistic roles are not fully understood.

Anomalous Spectral Shift of Near- and Far-Field Plasmonic Resonances in Nanogaps.

The near-field and far-field spectral response of plasmonic systems are often assumed to be identical, due to the lack of methods that can directly compare and correlate both responses under similar environmental conditions. We develop a widely tunable optical technique to probe the near-field resonances within individual plasmonic nanostructures that can be directly compared to the corresponding far-field response. In tightly coupled nanoparticle-on-mirror constructs with nanometer-sized gaps we find >40 meV blue-shifts of the near-field compared to the dark-field scattering peak, which agrees with full electromagnetic simulations.

Mapping ear canal movement using area-based surface matching.

Movement of the external ear canal, associated with jaw motion, relative to the concha region of the pinna has been studied. Pairs of open-jaw and closed-jaw impressions were taken of 14 ears from 10 subjects. Three-dimensional coordinate data were obtained from the concha and the anterior surface of the canal using a reflex microscope.