Tuesday, 26 April 2016 (PhD Presentation)

Dynamic Optical Sampling by Cavity Tuning and its Applications in Ranging, Imaging, and Spectroscopy

Speaker: Lin Yang (UAH Physics)
Location: OPB 234, 2:00pm (Note the time)
Abstract: In this dissertation, a dynamic model of optical sampling by cavity tuning (OSCAT) was developed for a various type of potential applications in different fields. A OSCAT-based test bed was designed and built. Demonstrations of its applications in ranging, imaging and spectroscopy are presented. For the application in ranging and remote motion tracking, target vibration has been successfully detected at an equivalent free-space distance of more than 2 km, with line-of-sight oscillations as small as 15 μm peak-to-peak and as fast as 50 Hz faithfully detected. Scan rates up to 1 kHz have been experimentally demonstrated with our current OSCAT system. For the application in depth-resolved imaging and 3D profilometry, different types of samples are imaged and the 3D surface profile of a UAH key chain has been obtained. For the application in spectroscopy, the absorption spectrum of HCN gas has been achieved by the femtosecond laser-based Fourier transform (FT) spectroscopy. The overall shape of the HCN absorption spectrum is also sketched out by an OSCAT-based FT spectrometer. Limitations and possible issues are discussed for each application, respectively.

Tuesday, 19 April 2016

High Temperature Thermoelectrics

Speaker: Dr. Dennis Tucker (MSFC)
Location: OPB 234, 2:30pm
Abstract: Radioisotope thermoelectric generators (RTG’s) convert heat from plutonium oxide into electricity using the Seebeck Effect. SiGe and PbTe are the normal thermoelectric materials used in RTG’s for this conversion. Both must use a cover gas to mitigate evaporation of the material while in use. Thermoelectric efficiency can be increased by utilizing higher operating temperatures. At the present time, this is limited to 1275K for the PbTe thermoelectric material. We are presently studying perovskite materials as a possible replacement thermoelectric. Barium titanate and barium strontium titanate can be appropriately doped resulting in both n-type and p-type semiconductors necessary to produce a thermoelectric generator. These materials will not require a cover gas. A review of thermoelectric physics will be given along with the experimental approach we are using to produce perovskite thermoelectric materials.

Tuesday, 12 April 2016

No Seminar Today. UAH Honors Day

Tuesday, 5 April 2016

No Seminar Today

Tuesday, 29 March 2016

Bringing Black Holes Together: How Supermassive Black Hole Binaries Form and Plunge Through the Final Parsec

Speaker: Dr. Kelly Holley-Bockelmann (Vanderbilt)
Location: OPB 234, 2:30pm
Abstract: Astronomers now know that supermassive black holes reside in nearly every galaxy. Though these black holes are an observational certainty, nearly every aspect of their evolution -- from their birth, to their fuel source, to their basic dynamics -- is a matter of lively debate. In principle, gas-rich major galaxy mergers can generate the central stockpile of fuel needed for a low mass central black hole seed to grow quickly into a supermassive one. During a galaxy merger, the black holes in each galaxy meet and form a supermassive binary black hole; as the binary orbit shrinks through its final parsec, it becomes the loudest gravitational wave source in the Universe and a powerful agent to sculpt the galactic center. This talk will touch on some current and ongoing work on refining our theories of how supermassive black hole binaries form, evolve within, and alter their galaxy host.

Tuesday, 22 March 2016

Spring Break

Tuesday, 15 March 2016

Transdisciplinary Materials Science and the Large Chamber Scanning Electron Microscope

Speaker: Dr. Edward J. Kintzel, Jr. (WKU)
Location: OPB 234, 2:30pm
Abstract: For materials scientists, conventional scanning electron microscopes place a limitation on the size of the object to be tested. Samples are typically small, and on the order of ten to a hundred millimeters in diameter. Given this constraint, there is a limit on the samples that can be nondestructively analyzed using this important testing technique. The Large Chamber Scanning Electron Microscope (LC-SEM) is an answer to overcome this and many other challenges in nondestructive analysis. Transdisciplinary research can be carried out that previously has not been possible. Examples will be presented to illustrate the ability to nondestructively interrogate large samples, prototype samples and large numbers of samples. Additionally, the LC-SEM can be used for in-situ real-time observations of the deformation behavior of materials. No other conventional SEM has the capability to actively observe the dynamic response of a variety of materials. Future research opportunities will illustrate the potential to span the academic, industrial, and government communities.

Tuesday, 8 March 2016

The LEAP Gamma-Ray Burst Polarimeter for the International Space Station

Speaker: Dr. Stephen Daigle (MSFC)
Location: OPB 234, 2:30pm
Abstract: The LargE Area burst Polarimeter (LEAP) concept for the International Space Station (ISS) is currently being developed for a future NASA Missions of Opportunity proposal by Marshall Space Flight Center, University of New Hampshire, and Yamagata University in Japan. The primary goal of LEAP is to measure polarization from gamma-ray bursts (GRBs) between 50-300 keV. The ISS will provide a zenith pointed platform to maximize the exposure to deep space and can accommodate a large area detector. Measuring the polarization for a large number of GRBs with LEAP is the key to breaking degeneracies between GRB models. This talk will examine the principle of operation of a Compton-scattering polarimeter and design considerations for the LEAP instrument.

Tuesday, 16 February 2016

Gravitational Waves and Their Detection

Speaker: Drs. Richard Lieu & Don Gregory (UAH)
Location: OPB 234, 2:30pm
Abstract: The basic physics for an essential understanding of the recent LIGO discovery of gravitational waves is presented with minimal reliance on General Relativity.  The extreme precision measurement of distances by interferometry in a classic optical system, which played a vital role in LIGO's success, will also be described.

Tuesday, 9 February 2016

Nonlinear Duffing Oscillator Model for Third Harmonic Generation 

Speaker: Dr. Michael Scalora (US Army)
Location: OPB 234, 2:30pm
Abstract:  We employ a classical, nonlinear Lorentz-Duffing oscillator model to predict third harmonic conversion efficiencies in the ultrafast regime, from a variety of metal nanostructures, including smooth, isolated metal layers, a metal-dielectric photonic band gap structure, and a metal grating. As expected, the plasmonic grating yields the largest narrow-band conversion efficiencies. However, interference phenomena at play within the multilayer stack yield comparable, broad-band conversion. The method includes both linear and nonlinear material dispersions that in turn sensitively depend on linear oscillator parameters. Concurrently, and unlike other techniques, the integration scheme is numerically stable. By design, one thus avoids the introduction of explicit, third-order nonlinear coefficients and also takes into account linear and nonlinear material dispersions simultaneously, elements that are often necessary to fully understand many of the subtleties of the interaction of light with matter.

Tuesday, 2 February 2016

High Resolution, Lightweight X-ray Optics for Astronomy 

Speaker: Dr. Carolyn Atkins (NASA MSFC)
Location: OPB 234, 2:30pm
Abstract: One of the challenges faced within the astronomical X-ray community is how to produce lightweight high angular resolution optics for a future X-ray mission capable of probing the early X-ray universe. One such mission concept, X-ray Surveyor, is designed specifically to meet this need and is currently being studied by NASA in preparation for the 2020 decadal; however, a significant improvement in either optics fabrication or optics correction is required to make this concept a reality. This seminar will provide an overview of several technologies being employed to achieve this goal and in particular the focus will be on optics correction via techniques such as active/adjustable X-ray optics and thin film correction by differential deposition. Presentation

Tuesday, 26 January 2016 (Two 30 Minute Talks)

New Probabilistic Model for Episode Integrated Fluences of Protons using Episodes from 1973-2013 

Speaker: Mr. Zach Robinson (UAH/Physics)
Location: OPB 234, 2:30pm
Abstract: A new probabilistic model for protons has been created using episode integrated fluences. This model will allow the user to choose a mission start date, mission duration, and confidence level to construct a mission-specific, bounding case spectrum for proton fluences at a distance of 1 AU from the sun. A new database of episode integrated fluences will be created for this model. The database will contain 29 channels that span the energy range 0.88-485 MeV. This database will cover the period from November 1, 1973 to December 31, 2013, making it the largest database on solar activity.

Bow Shocks, Cold Fronts, and Substructures in Merging Galaxy Clusters 

Speaker: Mr. Sarthak Dasadia (UAH/Physics)
Location: OPB 234, 2:30pm
Abstract: Galaxy clusters are the most massive gravitationally bound objects in the universe. In the hierarchical scenarios of the large-scale structure formation of the universe, they form by subcluster mergers. Such mergers inject tremendous amounts of energy (~1064ergs) into the intra-cluster medium (ICM). A large fraction of this energy is dissipated through heating ICM gas via shocks. I will present Chandra observations of two merging galaxy clusters: 3C89 & Abell 665. 3C89 adds a unique bow shock system associated with a wide-angle tail (WAT) radio galaxy and several intriguing substructures. I will also discuss our recent discovery of a robust shock front in Abell 665 that is consistent with the Mach number M ~ 3.

Tuesday, 19 January 2016

Nonlinear Dynamics in Optimal Communication Waveforms 

Speaker: Dr. Ned J. Corron (U.S. Army)
Location: OPB 234, 2:30pm
Abstract: Modern communication technology is built upon the foundation established by Nyquist, Shannon, Wiener and others in the 1940s, whose theories enabled the rigorous derivation of optimal solutions to practical communication problems. In this talk, we apply the methods of communication theory to derive optimal waveforms for transmitting information through noise using very simple filters as receivers. Specifically we presume passive, linear RLC filters and derive the communication waveforms that maximize the receiver signal-to-noise performance. From routine application of standard methods, we surprisingly find that the optimal communication waveforms are provably chaotic. We extrapolate from simple examples to argue that the optimal communication waveform for any stable infinite impulse response filter is similarly chaotic. If true, this conjecture implies the phenomena of nonlinear dynamics and chaos are fundamental and essential to full understanding of modern communication theory.

Tuesday, 12 January 2016

Experiment Test of a Quantum Measurement Technique to Overcome the Nyquist Limit 

Speaker: Dr. Richard Lieu (UAH/Physics)
Location: OPB 234, 2:30pm
Abstract: In recent literature, three independent quantum-theoretic calculations consistently refuted an earlier claim of Lieu et al (2014) that beam splitter intensity subtraction, the homodyne technique, followed by high time resolution sampling can lead to the detection of the brightness of incoherent light at the shot noise limit. In this talk I present an extensive and detailed experimental assessment of the performance of homodyne detection. Using two beam splitters, sandwiched by a piece of rotating ground glass to introduce incoherence, the intensity of a laser reference signal is measured (a) before, and (b) after contamination by photon bunching noise, almost exactly simultaneously. Moreover, the measurement in (b) was done in two ways: direct and homodyne, also with no appreciable time delay. The sampling rate of all measurements is the same, and is always higher than the frequency limit of the classical bunching noise. By carefully comparing the resulting three time series, it is found that the homodyne detection of the incoherent signal resembles more closely the variance and variability pattern of the original coherent signal, and the effect is more prominent when the sampling frequency is higher. It would therefore appears that the quantum phenomenon of shot noise can be used to overcome the Nyquist theorem, by combining the homodyne technique with sampling at a rate faster than the classical noise fluctuations it is possible to surpass the sensitivity limit of the radiometer equation.