1. Tunable Aerogel Waveplates Yoonseok Lee, University of Florida, DMR 0803516 Understanding the effect of anisotropic disorder on the superfluid phases of 3 He in high porosity silica aerogel has been a subject of recent investigations. We proposed that global anisotropy can be introduced by uniaxially compressing or stretching the aerogel and theoretical calculations in this system indicate a widened A-like phase region and/or a new superfluid phase. For a systematic investigation, a quantitative characterization of the amount of the anisotropy generated by compressing or stretching is necessary. We conducted the room temperature optical birefringence measurements of 98% porosity silica aerogel samples subjected to various degrees of uniaxial compression up to 15% strain, over 200 to 800 nm wavelengths. Uniaxial compression of aerogel introduces global anisotropy, inducing birefringence in the material. We observed a quasi-linear strain dependence in birefringence, the difference in the indices of refraction between two polarization parallel and perpendicular to the compression axis. Our study demonstrates that uniaxially strained high porosity aerogels can be used as tunable waveplates in a broad spectral range. This work was featured as a news item in Ceramic Tech Today by the American Ceramic Society. P. Bhupathi et al., Optics Express 17, 10599 (2009). When linearly polarized light (45° relative to the compression) passes through the compressed aerogel (top figure), the character of polarization is modified by optical birefringence of the aerogel. The light intensity for various angles of the analyzer is plotted in the graph above. Especially, the node point indicates that the linearly polarized light turns into circularly polarized beam.

2. Tunable Aerogel Waveplates Yoonseok Lee, University of Florida, DMR 0803516 Outreach This work initially started as an undergraduate research project and has evolved into a group effort involving graduate, undergraduate, and high school students. In 2008 Summer, a high school student, Jackson Blankstein from Alexander W. Dreyfoos School of the Arts in West Palm Beach, FL participated in this project through UF Student Science Training Program (SSTP). He conducted birefringence measurements for one 98% aerogel sample reported here and completed analyses of his results. Through this project, the student learned the concept of light polarization, took data using research quality instrument, microscope photometer, and completed his analyses using a standard data analysis software, Origin. He is a coauthor of a paper published in Optics Express and presented his work at the local science fair. He was chosen as one of the finalists for the state level science fair and decided to apply to UF as a physics major. Technological Impact This work suggests a potential application of aerogel as broadband tunable waveplates. Aerogel waveplates might have certain advantages compared to the Babinet compensator, which is a most commonly used tunable waveplate: uniform phase retardation in the whole device, low (even first) order waveplates, easy calibration, and multiple adjustable parameters (thickness of the sample, degree of compression, and porosity). Based on this work, a provisional US patent was applied.