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Physics and Astronomy

KAPAO Prime: Informing the Final System

Daniel Contreras (2013); Student Collaborator(s): Erik Littleton (2013 HMC); Lorcan McGonigle (2013); William Morrison (2012); Jonathan Wong (2015); Mentor(s): Philip Choi; Scott Severson*
*Sonoma State University

Abstract: We present the current status of the prototype for KAPAO, an adaptive optics (AO) instrument in development for the Pomona College Table Mountain Observatory (TMO) 1-meter telescope. The system will be based around custom optics, a tip-tilt mirror, a 140-actuator microelectromechanical deformable mirror (MEMS DM) and a 1kHz wavefront sensing camera (WFS). In the final stages this system will deliver an order-of-magnitude improvement over the current TMO seeing limits. Research this summer was performed on the active prototype system gathering on-sky data at TMO as well as a testbed system on Pomona’s campus. The variety of tests being performed include integrating the system with the telescope, investigations in optical throughput and image quality, and developing tools to critically analyze the performance of the AO loop software. This research is important to the initial development of the final system scheduled for completion by summer 2013. Beginning construction of this final system is the next major step for the KAPAO team.
Funding Provided by: The Rose Hills Foundation (DC); Sherman Fairchild Foundation (LM); Pomona College Astronomy & Physics Department (JW); National Science Foundation - AST-0960343 (PC, WM)

Population Synthesis of Globular Clusters

Claire Dickey (2014); Student Collaborator(s): Anne Hedlund (2014); Mentor(s): Philip Choi

Abstract: This summer we characterized the unresolved portions of simple stellar populations. We examined seven clusters in the Large Magellanic Cloud in two optical wavelengths and extracted color and brightness information for spatially resolved stars, as well as the total light from each cluster. Based on the ratio of resolved light from individual stars to the integrated cluster flux and the constraints of current stellar evolution models, we created models of the clusters past the observational limits. Thus far, we have shown that the initial mass function for these clusters varies from a power-law slope of 0.10 to 0.30, while later phases of stellar evolution are universal between clusters.
Funding Provided by: Sherman Fairchild Foundation (DC); Paul K. Richter and Evalyn E. Cook Richter Memorial Funds (AH); Observatories at the Carnegie Institute of Washington

KAPAO Prime: Design

Lorcan McGonigle (2013); Additional Collaborator(s): Scott Severson*; R. Erik Spjut (HMC); Mentor(s): Philip Choi
*Sonoma State University

Abstract: KAPAO Prime (KAPAO A Pomona Adaptive Optics instrument) is the final optical system designed in Zemax Optical Design Software that uses four custom-made off-axis paraboloid (OAP) mirrors to collimate light for a deformable mirror and focus light onto a science camera. Prime is characterized by diffraction limited imaging over the full 73” field of view of the Andor Camera at f/33 as well as for the NIR Xenics camera at f/50. In Zemax, tolerances of 1% on OAP focal length and off-axis distance were shown to contribute an additional 4 nm of wavefront error (98% confidence) over the fov of the Andor camera; the contribution from surface irregularity was determined analytically to be 40nm for λ/10 OAPs. Modeling of temperature deformation in SolidWorks revealed 70 micron contractions along the edge of the board for a decrease of 75°F; such displacements are predicted to contribute an additional 20 nanometers of wavefront error. Flexure modeling is on-going. Following a final design review, we are hoping to begin alignment and testing in Q1 2013.
Funding Provided by: Sherman Fairchild Foundation; National Science Foundation - AST-0960343

An Entangled Photon Approach to Anticoincidence Experiments and Quantum Erasure

Alex Cole (2015); Student Collaborator(s): Dorothy Silverman (2014); Mentor(s): Alfred Kwok

Abstract: We generated entangled photons via type I spontaneous parametric down-conversion in a betabarium borate (BBO) crystal. Entangled photons are in a single-photon state, so they do not get split by a beamsplitter. This leads to a measured second-order temporal coherence value of g(2)(0)=0, in violation of the classically-derived inequality g(2)(0)≥1. This experiment shows the granular/particle nature of light, that is, the existence of the photon. We also developed framework for a quantum eraser that emphasizes the trade-off between "which-path" information and interference patterns suitable for teaching labs.
Funding Provided by: The Rose Hills Foundation

High Resolution Fourier-Transform Microwave Spectroscopy of YbF

Benjamin Girodias (2015); Student Collaborator(s): Zachary Glassman (2014); Additional Collaborator(s): Timothy Steimle*; Jens-Uwe Grabow† Mentor(s): Richard Mawhorter
*Arizona State University; †Leibniz University Hannover (Germany)

Abstract: A wide variety of theories beyond the standard model predict that the electron has a shape, or electric dipole moment, denoted eEDM. The most successful method for determining eEDM upper limits uses open shell molecules, such as YbF. They have huge internal electric fields, which can be used to provide measurable differences between the aligned and anti-aligned dipole states. Hence, a deep understanding of the structure of this molecule is important for future eEDM experiments. Analyzing previous optical data, we predicted the location of new spectral lines using the program SPCAT. Then using Fourier Transformation microwave spectroscopy, we measured the 4 known 174YbF lines in addition to 12 new 14 GHz lines of the remaining even and 171YbF isotopologues. This new information will improve current experimentally determined constants and will allow us to investigate the phenomenon of Born-Oppenheimer Breakdown. New RbF lines were also observed to probe other electronnucleus interactions.
Funding Provided by: Pomona Alumni SURP Fund (BG); Sherman Fairchild Foundation (ZG); Sontag Research Fellowship (RM)

Growth and Characterization of Single-Layer Graphene Films

Eric Puma (2014); Additional Collaborator(s): Paul McEwen*; Mentor(s): David Tanenbaum
*Cornell University

Abstract: Graphene, a single-layer carbon nanostructure, has piqued the interest of the scientific community in recent years as a result of its intriguing mechanical, optical, thermal, and electrical properties. Here at Pomona, the successful growth of high quality graphene would unlock a wide range of potential experiments and applications, including use as a transparent electrode for solar cells. We worked towards the growth of single-layer graphene on copper foil via chemical vapor deposition, characterizing our results with SEM Imaging and Raman Spectroscopy. With a new Raman tool at our disposal, we determined growth attempts from prior years to be, in many cases, graphitic (multi-layer) and have since been refining our growth process in hope of attaining single-layer films. We have achieved significantly improved understanding of the characterization techniques and are on the path to attaining single-layer results.
Funding Provided by: Pomona Alumni SURP Fund; Cornell University; National Science Foundation - DMR-1126080

Inverted P3HT:PCBM Organic Photovoltaic Cells

Emily Yang (2014); Mentor(s): David Tanenbaum

Abstract: The race for renewable energy has led scientists to tap into the sun’s energy with organic photovoltaics (OPVs). These solar cells can be prepared from inks similar to traditional print media and thus are potentially more cost-efficient than the inorganic photovoltaics most often used today. However, compared to their conventional counterparts, OPVs lack in both efficiency and stability, and rely on an expensive and brittle transparent conducting electrode made of indium tin oxide (ITO). Inverted poly (3-hexylthiophene) (P3HT), [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) solar cells were fabricated and tested with an updated automated characterization system designed to track 20 solar cells. After experimentation with differing anneal times, the inclusion of hole-conducting poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), and application of a reverse bias pulse, the longest cell lifetime under simulated full sun conditions was found to be over 1000 hours and counting, and the highest power conversion efficiency (PCE) was 1.117%. Cells stored in darkness appeared to have little or no cell degradation.
Funding Provided by: The Rose Hills Foundation; Cornell Center for Nanoscale Systems; National Science Foundation - DMR-1126080

Seed Flight: The Explosive Seed Dispersal of the Acanthaceae

Carolyn Cross (2013); Mentor(s): Dwight Whitaker

Abstract: The Acanthaceae, a family of plants containing approximately 2500 species, has evolutionarily developed an explosive seed dispersal mechanism. During this dispersal process, the seeds can reach an initial translational velocity of up to 15 meters per second and a rotational velocity anywhere from 100 to 1500 Hertz depending on the species. This dispersal process, lasting on the order of milliseconds and flinging seeds up to several meters away, can be analyzed through the use of a high-speed video camera. This analysis suggests a direct correlation between the translational and rotational velocities of the seed. Moreover, a graph of these two quantities is segmented greatly based on species: the larger, more curved seeds correlate to lower velocities whereas the smaller, more symmetrical seeds are connected to both greater translational and rotational velocities. We aim to examine fluid dynamics in the practical sense by mimicking these initial flight conditions in order to determine the most stable and efficient form of flight based on species.
Funding Provided by: Pomona College SURP

Lasers Cool: Seeking A Bose-Einstein Condensate

Shannon Lubetich (2015); Student Collaborator(s): Charles Owens (2014); Mentor(s): Dwight Whitaker

Abstract: In this research, our goal is to create a Bose-Einstein Condensate, which is a state of matter in which all the bosons in a system fall into the quantum ground state. To reach this state, a system of identical bosons must be cooled to near absolute zero. A combination of lasers tuned near the atoms’ atomic transition and a magnetic field confines and cools Rubidium-87 atoms in a vacuum chamber at temperatures on the order of a few hundred micro-Kelvins. Progress was made in creating denser MOTs, and altering our critical timing command system through LabVIEW, which enables more precise operation and allows us to cool to lower temperatures. We have also improved the software for creating and imaging the atoms through the use of remote slide presentation controllers.
Funding Provided by: Pomona College SURP

Inertial Particle Transport from Sphagnum Moss Vortex Rings

Samuel Whitehead (2013); Mentor(s): Dwight Whitaker

Abstract: We present a numerical analysis of how vortex rings from Sphagnum moss disperse their spores. Comparisons of the results of our CFD model with data measured from high-speed video reveal that the pressure inside the capsules is only 2 atm, which is significantly less than has been reported in the literature. Moreover vortex rings produced by these pressures do not optimize the impulse to the fluid as is seen in other biological systems. Here we present an analysis of the efficiency with which vortex rings from Sphagnum transport spores to heights where they can be carried by wind currents. Spore trajectories determined from a modified Maxey-Riley equation form a dynamical system for which we find the Lagrangian coherent structures (LCS), which define regions where spores are entrained in the vortex bubble. By analyzing the dependence of the LCS on spore size, capsule pressure, and morphology we will assess the efficiency with which vortex rings from Sphagnum transport spores.
Funding Provided by: Pomona College SURP

gri Blazar Monitoring and Polarimetry

Meredith Durbin (2014); Student Collaborator(s): Erika Carlson (2015); Robby Goldman (2015); Mentor(s): Alma Zook

Abstract: We report on continued gri monitoring and polarimetry of a total of ten blazars over June and July 2012, as well as seven standard stars with known polarizations. All the blazars observed are quiescent, and most have been monitored for several years, starting in 2005. The standard stars allow us to test the accuracy of our blazar polarimetry measurements.
Funding Provided by: Sontag Research Fellowship; Pomona College Astronomy & Physics Department (MD); Pomona College SURP (RG)

Characterizing Pomona College's Polarimeter

Robby Goldman (2015); Student Collaborator(s): Meredith Durbin (2014); Erika Carlson (2015); Mentor(s): Alma Zook

Abstract: We operated Pomona College's polarimeter to measure the polarization of several blazars. Before analyzing these measurements, we ran two controlled tests on the polarimeter to identify any sources of experimental uncertainty and systematic error. The first test determined how the size of the uncertainty of our polarization measurements for an object depended on its brightness; we discovered that our uncertainty is greater for fainter objects. However, we also discovered that the polarimeter yields the lowest polarization measurements for extremely bright and extremely faint objects. The second test revealed that the polarimeter measures slightly different polarizations for an object depending on the 180-degree interval of data collection. For all our data of strongly polarized objects, we found that every cosine curve we fit to the data has a positive y-offset. Although we do not know the cause of this systematic error, it does not affect the calculated polarization of each object.
Funding Provided by: Pomona College SURP (RG); Pomona College Astronomy & Physics Department (MD); Sontag Research Fellowship

Research at Pomona