Bulletin of the American Physical Society
2008 Joint Meeting of the APS Ohio-Region Section, the AAPT Southern Ohio Section, and the ACS Dayton-Section
Volume 53, Number 8
Friday–Saturday, October 10–11, 2008; Dayton, Ohio
Session C8: Applied Physics and Optics |
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Chair: Michael Marciniak, Air Force Institute of Technology Room: Fawcett Hall 210 |
Saturday, October 11, 2008 8:00AM - 8:12AM |
C8.00001: The Bi-Directional Reflectance Distribution Function (BRDF) -- Measurement and Analysis Techniques Bradley Balling, Michael Marciniak The Bi-Directional Reflectance Distribution Function (BRDF) either defines or represents how light reflects off a surface; it is a subset of the larger family of Bi-Directional Scatter Distribution Functions which include transmission distribution, as well. This work seeks to define and explore the BRDF through the use of both analytic and measurement techniques. Both representative and more physically based BRDF models are fit to data collected from a variety of samples using a Schmitt Industries' Complete Angle Scatter Instrument. In particular, a measurement methodology and statistical analysis of a calibrated diffuse reflectance standard supplied by the National Institute of Standards and Technology (NIST) will be presented to demonstrate the repeatability of the measurement technique and just how much directional dependence a real-world ``perfectly diffuse'' reflector actually has. Analysis shows that the more physically based BRDFs do represent measured data more accurately, and hold the potential to be predictive, rather than merely a representation of previously measured surfaces. [Preview Abstract] |
Saturday, October 11, 2008 8:12AM - 8:24AM |
C8.00002: Rugged TDLAS system for High Energy Laser atmospheric propagation characterization Glen Perram, Christopher Rice An active remote sensing instrument for the characterization of atmospheric absorption, scattering, and scintillation at several key high energy laser wavelengths is in development. The instrument is based on narrow band tunable diode lasers fiber coupled to a 12'' Ritchey-Chretien transmit telescope and a second receive telescope with visible or near infrared imager. For example, tunable diode lasers have been used to obtain absorption spectra in the laboratory for the Cs D2 lines near 852 nm and the oxygen X-b lines near 760 nm, key to the Diode Pumped Alkali Laser (DPAL) concept. Absorbencies of less than 0.5{\%} are observable. Applications will be assessed including effects to HEL atmospheric propagation from molecular and aerosol absorption and scattering, Cn2 estimation from atmospheric turbulence, hazardous chemical emission detection, and laser communication interception from side scattering. The system will soon be deployed to a military laser test range to characterize path lengths of greater than 1 km. [Preview Abstract] |
Saturday, October 11, 2008 8:24AM - 8:36AM |
C8.00003: Wave Optics Simulation and Prediction of Retro-reflections from Optical Systems John Tatar, Walter Cole, Michael Marciniak Optical devices interrogated with a laser in the appropriate band can exhibit strong retro-reflections of the incident beam, a characteristic that could be exploited for optical target detection and identification. The distribution of reflected power is strongly dependent on the geometry of the interrogation scenario, atmospheric conditions, and the cross section and reflectivity of the target optical device. Wave optics simulations and field tests are used to characterize the spatial distribution of reflected power from a corner cube and a lens-reflector target at varying focus. [Preview Abstract] |
Saturday, October 11, 2008 8:36AM - 8:48AM |
C8.00004: A Transformer with Unequal Mutual Inductances Xiaodong Liu, Yu Liang, Qichang Liang We designed a new kind of transformer which is composed of a circular parallel plate capacitor and a toroidal solenoid. The toroidal solenoid is placed in the middle of the parallel plate capacitor. The circular parallel plate capacitor is used as the primary coil and the toroidal solenoid is used as the secondary coil. The toroidal solenoid could enclose air or magnetic material inside the solenoid. Numerical calculations and analyses show that this transformer has unique characteristics of unequal mutual inductances due to the displacement current. The displacement current between the plates of the capacitor contributes to the mutual inductance from the capacitor to the solenoid, while the gap between the plates reduces the mutual inductance from the solenoid to the capacitor. The mutual inductance from the solenoid to the capacitor is always less than that from the capacitor to the solenoid. This is the first transformer in the world which has unequal mutual inductances. It is anticipated that this specific device has potential applications in power transmission at radio frequency. [Preview Abstract] |
Saturday, October 11, 2008 8:48AM - 9:00AM |
C8.00005: Multipactor Discharge Mitigation in High Power Microwave, HPM, Systems Neil Rogers, William Bailey A multipactor discharge is an electron avalanche supported by secondary electron emission that can couple the HPM field energy to a waveguide dielectric window. The energy deposition can lead to the destruction of the dielectric material and catastrophic window failure. Mitigation approaches for this single surface multipactor at dielectric windows are investigated using Particle-In-Cell simulations. Initially baseline susceptibility diagrams are constructed analytically and compared with self-consistent, dynamic system trajectories. Geometric mitigation is then considered by varying the window orientation with respect to the HPM electric field. Small angular deviations, less than 20 degrees, from the nominal case of the electric field parallel to the surface show dramatic changes in the susceptibility diagram. A materials approach to mitigation is then considered. Titanium Nitride, TiN, coatings applied to the dielectric surface can substantially reduce the secondary emission yield. Representative TiN modifications of the virgin secondary emission yield are simulated and the resulting susceptibility diagrams are discussed. [Preview Abstract] |
Saturday, October 11, 2008 9:00AM - 9:12AM |
C8.00006: Bi-directional Scatter Distribution Function (BSDF) Measurements of Large Area Photonic Crystals Robert Lamott, Michael Marciniak, Brian Cunningham Optical metamaterials, or photonic crystals (PCs), are lattice structures made of two or more materials with different refractive indicies with the structure repeating at a sub-wavelength period. This results in a photonic bandgap within the material, completely rejecting certain wavelengths, similar to an electronic bandgap within a semiconductor. Recent developments have allowed the production of PCs with large areas, suitable for analysis using standard optical techniques. Using a large sample of a two-dimensional PC designed to reject 532nm at normal incidence, we investigated the Bi-directional Scatter Distribution Function (BSDF) of the material using a Complete Angle Scatter Instrument (CASI) with a 544nm laser, with the goal of modeling its BSDF. Despite the difference between the laser and the PC's design wavelengths, several interesting features were apparent, including anomalous reflection and transmission at 22degrees from normal regardless of the incident angle, and strong scattering in all directions for a 22degrees incident angle. Since most computationally efficient BSDF models are parameterizations of measured data, these features drastically increase the difficulty of BSDF modeling as no existing model can account for them. [Preview Abstract] |
Saturday, October 11, 2008 9:12AM - 9:24AM |
C8.00007: A SWNT Synthesis Apparatus for Multivariate Analysis of Nucleation and Growth Factors R. Acosta, D.C. Liptak, R. Rao, P. Caceres-Valencia, J. Deibel, B. Maruyama A Multivariate analysis of various factors that influence the nucleation and growth of single-walled nanotubes (SWNTs) is demonstrated. The SWNTs are synthesized via thermal chemical vapor deposition on silicon substrates inside an environmental cell coupled to an automated stage. In-situ micro-Raman spectroscopy and imaging is performed on the radial breathing mode and D/G bands of the growing SWNTs where the excitation laser also serves as a localized heat source for SWNT growth. The SWNTS are grown on thermally isolated islands within the substrate and data can be collected by varying growth conditions in real time across each region. Computer control over substrate temperature, feed gas composition, chamber pressure and substrate position enable rapid exploration of the SWNT growth parameter space and the establishment of a robust database for comparison with theory. [Preview Abstract] |
Saturday, October 11, 2008 9:24AM - 9:36AM |
C8.00008: Agent-Based Models for Physics and Chemistry Paul Seybold A brief overview of the use of agent-based models for the simulation of the behaviors of complex systems will be given. It will be emphasized that these agent-based models are rule-based, rather than equation-based. Although the governing rules themselves may be quite simple, quite complex features can emerge from the simulations. Illustrations using stochastic cellular automata models of a chemicals reaction and the vapor-liquid phase transition will be presented. [Preview Abstract] |
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