Location: Physics Bldg., room 401

Location: Physics Bldg., room 401

You are all invited to attend Nathan's PhD defense.

Date: Monday, November 23, 2009
Time: 10:00 am
Location: PHYS 401

TITLE:
Application of satellite laser altimetry data to studies of sea ice properties and processes

ABSTRACT:
Sea ice plays an important role in the global climate system by impacting the energy balance of the Earth as well as affecting the oceanic and atmospheric circulations. Recently, large changes have been observed in the Earth's areal coverage of sea ice. However, little is currently known about sea ice thickness particularly at the scales needed for climate research. Spaceborne remote sensing provides the necessary global scale of coverage, but the retrieval of sea ice thickness from space has not been possible until recently with the launch of satellite altimeters of high accuracy and precision. The Ice, Cloud, and land Elevation Satellite (ICESat) is one such laser altimeter with the potential to retrieve sea ice freeboard, which, when combined with snow depth retrievals and the assumption of hydrostatic balance allows for the determination of sea ice thickness. The goal of this study is to use data from ICESat to provide sea ice thickness values at the global scale and high spatial resolution needed for climate studies. The work presented in this thesis includes the validation and improvement of ICESat data products, development and validation of sea ice freeboard retrieval algorithms using the ICESat data products, and the development of a method to combine ICESat freeboard retrievals with a snow depth data set to determine sea ice thickness at the 70 m spatial resolution of ICESat. The ICESat data set is used to study sea ice thickness, heat exchange, and ice production in the Arctic Ocean for the 2003-2008 time period. Despite the thinning of the Arctic sea ice cover over the 2003-2008 time period, mean ice growth rates for consecutive fall and winter measurement periods remained relatively constant. An increased ice growth rate which may be expected from a thinner ice cover appeared to be balanced by warmer temperatures. An increased ocean-atmosphere heat flux is also observed due to the thinning of the sea ice cover.

The 3-D movie experience has improved quite a bit since the “golden era” of the 1950’s…the special effects are now so realistic that you are almost guaranteed to spill your popcorn when the monster jumps off the screen! In this talk I will review the basic operating principles of modern 3-D movie systems, which are built upon the clever use of a few key concepts from undergraduate optics.

Location: Physics Bldg., room 401

Nestor successfully defended his masters thesis on November 13, 2009

TITLE:
Broad band terahertz time domain spectroscopy on polymers and organic electro-optic polymers

ABSTRACT:
Several polymers and two organic polymer composites were studied using terahertz time domain spectroscopy and analyzed using Duvillaret’s method and a dynamic range analysis to determine their credible bandwidth. Terahertz time domain spectroscopy is a technique that allows us to determine the real index of refraction and the absorption of nonconductive materials in the terahertz band. These polymers are used as hosts to build organic composites for terahertz generation through optical rectification and detection via electro-optic (EO) sampling. Knowledge of their optical parameters is important when considering them as hosts for emitters and detectors. Also, the knowledge of these parameters over a wide bandwidth is important in the determination of the degree of phase matching that these materials can have, for a given center wavelength of an optical pump pulse. Broad bandwidth and a clear spectrum were achieved with an air-plasma emitter and an organic EO polymer sensor. In this thesis a bandwidth that goes from 0.7 to 9 THz for the real index of refraction and for the absorption coefficient for the majority of the polymers, is reported.

I thought I was a good teacher until I discovered my students were just memorizing information rather than learning to understand the material. Who was to blame? The students? The material? I will explain how I came to the agonizing conclusion that the culprit was neither of these. It was my teaching that caused students to fail! I will show how I have adjusted my approach to teaching and how it has improved my students' performance significantly.

Location: LH 5 (ECS Bldg)

We explore nonlinear optical phenomena at the nanoscale by launching femtosecond laser pulses into long silica nanowires. Using evanescent coupling between wires we demonstrate a number of nanophotonic devices. At high intensity the nanowires produce a strong supercontinuum over short interaction lengths (less than 20 mm) and at a very low energy threshold (about 1 nJ), making them ideal sources of coherent white-light for nanophotonic applications. The spectral broadening reveals an optimal fiber diameter to enhance nonlinear effects with minimal dispersion. We also present a device that permits a number of all-optical logic operations with femtosecond laser pulses in the nanojoule range.

Location: Physics Bldg., Room 401

Location: Physics Bldg., Room 401

The Fermi Gamma-Ray Space Telescope launched in June 2008 opening a new window on the highest energy sources in the universe. I will give a brief overview of how Fermi’s primary instrument, the Large Area Telescope (LAT), detects gamma-rays and its topics of study. One of the most exciting possibilities for the Fermi-LAT is the indirect detection of dark matter. Well-motivated and popular dark matter theory assumes that a significant component of dark matter is Weakly Interacting Massive Particles (WIMPs). I will go over WIMP basics, and the strategies involved in dark matter searches. Finally, I will talk about my work on the possibility to observe gamma lines from WIMP annihilation into gamma-gamma and gamma-Z final states. Detection of these lines would give convincing evidence for the existence of WIMPs and the WIMP mass.

Location: Physics Bldg., Room 401