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Physics and Astronomy

Click to watch Emily Chang '12 discuss her research project.

Caging Atoms with Light: The Magneto-Optical Trap

Rylan Grady ('13) ; Mentor: Dwight Whitaker

Abstract:  When cooled to the nano-Kelvin temperature range, a dilute gas of 87Rubidium atoms undergoes a phase change.  A large fraction of the atoms occupy the lowest possible quantum state, and a Bose-Einstein Condensate (BEC), a macroscopic system exhibiting quantum mechanical effects, is created.  To reach these temperatures we use a two-stage laser cooling process.  In the first stage, the Magneto-Optical Trap, we confine the Rubidium sample in a vacuum chamber with an anti-Helmholtz coil generated magnetic field.  By taking advantage of Rubidium’s hydrogen-like energy level structure, we are able to use the Doppler Effect to selectively alter the velocity of individual atoms, lowering the temperature of the sample by several orders of magnitude.  We create an image of the condensed cloud with a pulse of resonant light.  A revamping of the camera and software system improves data acquisition and automates analysis.
Funding Provided by: Pomona College SURP  

A Computational Fluid Dynamics Analysis of Sphagnum Moss's Vortex Ring Formation

Emily Chang ('12); Mentor: Dwight Whitaker

Abstract:  This project investigates the explosive spore dispersal of common peat moss (Sphagnum). Its 25 µm spores reach an initial velocity of 14 m/s in under 10 µs, and can get to heights of more than 10 cm. Analysis of high speed videos taken of the spore dispersal suggest that the spores are entrained in the ejected gas from the exploding capsule. This has been previously shown to be achieved through the formation of vortex rings. Video analysis techniques and computational fluid dynamics simulations were used to examine the mechanics of this explosion, and to investigate its optimality. The computer simulations model Sphagnum and aim to match our video data, and the effects of altering various experimental parameters on vortex ring formation were investigated.
Funding Provided by: Pomona College SURP  

KaPAO-Cam Alpha: Instrumentation

Daniel Contreras ('13); William Morrison ('12); Blaine Gilbreth ('11); *Scott Severson; Mentor: Philip Choi*Sonoma State University, Rohnert Park, CA

Abstract:  Our research involved the integration and testing of high-speed closed loop control software into Pomona College’s adaptive optics (AO) testbed. This software is a critical piece of the astronomical AO system meant to dramatically increase image performance on Pomona College’s Table Mountain Observatory telescope (TMO). The components under control include a deformable mirror, a wavefront sensor, and a piezo-electric tip-tilt mirror. Using a laser as a point source in our optical system, we were able to characterize aspects of our closed loop control and successfully close the loop to form diffraction limited images. The next step is to transfer this system to an optical breadboard-based prototype that will be tested on-sky at TMO. This system will use off-axis parabolic mirrors rather than lenses to increase optical throughput. With the unification of these components under software control, Pomona College’s adaptive optics instrument is one step closer to completion.
Funding Provided by: Rose Hills Foundation (DC) National Science Foundation ARRA Grant #AST-0960343 (PC) 

Polarization of Blazars

Frank Giron ('12); Charles Owens ('14); Mentor: Alma Zook

Abstract:  Blazars are black holes in the center of galaxies surrounded by an accretion disk of dust and gas. Using Pomona College’s one-meter telescope located in Table Mountain Observatory in conjunction with an attached CCD camera and a rotating Savart-plate polarimeter we found the percent of polarization from a selection of blazars (1510-089, BD+33 2642, HD 155197, and 1253-055). Polarization is believed to be due to synchrotron radiation. It refers to the relative orientation of the electric field vector to the direction of propagation of the light wave indicating the presence of strong magnetic fields and relativistic electrons. We took flats, dark-subtracted our images, and then normalized them. Using an image reduction program called IRAF (Image Reduction and Analysis Facility) we obtained a single file with only the necessary data on our blazars. The percent of polarization ranged from 2.16% to 2.37%. These results evidenced that synchroton radiation is present.
Funding Provided by: Pomona College SURP  

Graphene Growth and Transfer

Matt Hasling ('12); Emily Yang ('14); Benjamin Pollard ('11); Jenna deBoisblanc ('11); Mentor: David Tanenbaum

Abstract:  Graphene is a two dimensional hexagonal lattice of carbon atoms, which has many interesting properties, including transparency and high thermal and electrical conductivity. This investigation attempts to grow graphene through Chemical Vapor Deposition and transfer said graphene onto a substrate. The graphene is grown on square inch copper foils at 1000 degrees Celsius in a quartz vacuum chamber. The transfer onto silicon dioxide is done through multiple different methods, many involving a PMMA polymer sacrificial transfer layer resulting in varying quality of films. So far, a full graphene sheet has yet to be successfully transferred. Further work intends put the material to use as an electrode in organic solar cells.
Funding Provided by: National Science Foundation Subcontract through the Center for Nanoscale Systems at Cornell College Agreement 52611-8323 

Berkeley 87: Stellar Variability of a Young Star Cluster

Annie Hedlund ('14); Alana Shine ('14); Claire Dickey ('14); Mentor: Philip Choi

Abstract:  We used the Pomona College TMO 1-meter telescope to continue a photometric monitoring campaign of the star cluster, Berkeley-87.  The goal of this work is to investigate the angular momentum evolution in star-forming populations.  We obtained tri-color g-, r- and i-band observations on about 16 nights over 4 weeks.  Compared to prior observations, this summer's campaign utilized a refined observing technique that allowed for deep, multi-hour exposures and a 10x improvement in survey sensitivity.  We developed an automated reduction pipeline to process the raw images and used SExtractor, a source extraction software package to identify stars and create photometric source catalogs.  We’ve begun the preliminary characterization of the population based on (a) a multi-color photometric analysis of ~5000 stars detected in a super-deep 16-hour exposure and (b) photometric variability measurements that trace stellar rotation and thereby angular momentum.
Funding Provided by: Paul K. Richter and Evalyn E. Cook Richter Memorial Fund NASA Spitzer Grant (PC) 

Do Photons exist?

Kevin Ludlum ('13); Gretta Mae Ferguson ('13); Mentor: Alfred Kwok, Dwight Whitaker

Abstract:  We are setting up a lab to show the quantum nature of light. We have built an external cavity diode laser emitting light at 405nm. The laser light will undergo spontaneous parametric down-conversion and be split into two beams, one of which will be split again with a polarizing beam splitter. We will show the particle nature of light by demonstrating that the split beam is anti-correlated. Similar experiments have resulted in coincidence measurements over 100 standard deviations below the classical lower limit.
Funding Provided by: Pomona College SURP (KL, GMF) Pomona College Physics and Astronomy Dept. (KL) 

KaPAO-CAM Alpha: Design

Lorcan McGonigle ('13); Andrew Xue ('11 HMC); *Scott Severson;  Professor Erik Spjut†; Mentor: Philip Choi
*Sonoma State University, Rohnert Park, CA;  †Harvey Mudd College, Claremont, CA

Abstract:  We used off-the-shelf components to design and characterize an alpha test system for the final, fully custom optics system for KaPAO-Cam (a Pomona Adaptive Optics Camera). This system uses off-axis parabolic mirrors that collimate light for a deformable mirror (DM) and focus light onto the sensor of a science camera. Final image spots approach the diffraction limit over a 20 arcsecond field. The system uses a pair of achromatic doublets to expand the incoming beam to fill the DM, doubling the DM’s ability to correct without introducing additional aberrations. Analysis in ZEMAX, our optical design software, and SolidWorks, our 3D CAD design software, indicates that any flexure in the system should be insignificant when it is laid out on a 1” breadboard and attached to the telescope at seven mounting points. Real-world, closed-loop alignment has supported these simulations. In the future, we hope to mount the system on-sky to test functionality outside of the lab.
Funding Provided by: Paul K. Richter and Evalyn E. Cook Richter Memorial Fund (LM) National Science Foundation ARRA Grant # Grant #AST-0960343 (PC) 

Observing Blazars with Polarimetry

Charles Owens ('14); Frank Giron ('12); Mentor: Alma Zook

Abstract:  A blazar is made up of a galaxy that contains a supermassive black hole in its center. In this research, five objects (Blazars 1510-089, 1253-055, 1959+650 and 1652+398, and Polarization Standard Star BD+33 2642) were observed over an eight week period using polarimetry and photometry from the 1-meter telescope located at Table Mountain Observatory. Each object was observed using a Savart-plate polarimeter for the i-, r-, and g-filters. The data gathered was reduced using IRAF. In almost every measurement, the blazars were more strongly polarized than other observed objects in their star field. The strongly polarized light from these blazars indicates that synchrotron radiation was being emitted. This type of radiation implies that charged particles (electrons) and a strong magnetic field were present. However, it is not yet known what causes these electrons to be emitted at relativistic speeds or how the magnetic fields are formed.
Funding Provided by: Pomona College SURP  

Spectroscopy and Structure of LiKF2 Molecule

Derek Owens-Oas ('13); Jens-Uwe Grabow*;  Brian Drouin†; Mentor: Richard Mawhorter
*Institut für Physikalische Chemie und Elektrochemie, Leibniz Universität Hannover, Germany;  †Jet Propulsion Laboratory, Pasadena, CA

Abstract:  Using laser ablation microwave spectroscopy and three different isotopologues, we are attempting to unveil the molecular structure of a mixed dimer called LiKF2. We made strides in determining the values of three rotational constants, four nuclear hyperfine constants, two centrifugal distortion constants, and a few possible spin-rotation coupling constants as well. Because LiKF2 features two identical fermions, we studied the spin statistics and have successfully observed a 3:1 ratio of Ka odd-to-odd type energy level transitions over even-to-even. Similarly, we discovered a 1:2 ratio for the analogous case of identical bosons. This impacts the relative intensities and peak heights we observe in our spectra. We also discovered multiple occurrences of hyperfine triplet splittings where two of the three peaks are clearly visible. This suggests that there may be an additional parameter needed to model the LiKF2 molecule. We hypothesize that these splittings may be attributed to spin-rotation coupling.
Funding Provided by: Paul K. Richter and Evalyn E. Cook Richter Memorial Fund  

Total Internal Reflection Fluorescence Microscopy

Roger Sheu ('14); Glenn Flohr; Mentor: Alfred Kwok

Abstract: In total internal reflection fluorescence (TIRF) microscopy, a laser light bounces off an interface at an angle larger than the critical angle.  This results in an evanescent wave that penetrates into the sample being analyzed.  The intensity of the evanescent wave decays exponentially with sample depth, thus only illuminating the top ˜100 nm of the sample chamber.  This summer’s work has involved fine-tuning the experimental setup and carrying out several trials to verify TIRF.     We discovered that glycerol, which has been used as an index matching fluid between the TIR-prism and the quartz sample chamber, fluoresces.  This made visual observation of TIRF very difficult.  Nonetheless, we were able to obtain spectral and visual evidence for TIRF, although the intensity of the TIRF-spectrum was far weaker than the epifluorescence spectrum.
Funding Provided by: Paul K. Richter and Evalyn E. Cook Richter Memorial Fund  

Probing the Chemical Enrichment History of the Early Universe Using DLA and IGM Absorption Lines

Catherine Wilka ('12); Wallace L. W. Sargent*; Jason X. Prochaska†; Mentor: Bryan Penprase*California Institute of Technology;  †University of California, Santa Cruz, CA

Abstract:  All elements heavier than helium, including those in our planet and ourselves, were formed by stars or supernovae over the past 13.7 billion years. Studying the build-up of these elements, known as chemical enrichment, enables us to deduce the history of star formation and other physical processes. The goal of this SURP was to quantify element ratios (“metallicities”), in both massive clouds of hydrogen-rich gas called damped Lyman-alpha systems (DLAs) and the more diffuse intergalactic medium (IGM) in the early universe. We used high-resolution spectroscopic data from Keck for our measurements and analyzed the data with software scripted in IDL. We focused on trends in metallicities of DLAs and the CIV and OVI fractions in the IGM. We found evidence for a metallicity “floor” in DLAs, and our OVI abundances show no strong change with time, both in agreement with previous results from the literature.
Funding Provided by: Paul K. Richter and Evalyn E. Cook Richter Memorial Fund  

The Fabrication and Characterization of P3HT:PCBM Organic Photovoltaic Cells

Emily Yang ('14); Jenna deBoisblanc ('11); Mentor: David Tanenbaum

Abstract:  With the depletion of fossil fuel reserves and the threat of climate change, people are racing to tap into the sun’s energy with organic photovoltaics (OPVs). OPVs can be prepared from inks similar to traditional print media and forgo the large costs incurred by the inorganic photovoltaics most commonly used today. However, they are not as efficient or stable as their conventional counterparts and rely on a brittle and expensive transparent conducting electrode made of indium tin oxide (ITO). This summer we synthesized normal and inverted poly (3-hexylthiophene) (P3HT), [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) solar cells and tested them by measuring current voltage curves with an automated characterization system. For normal and inverted cells, our longest lifetimes were ~ 170 hours and 100 hours respectively, and our highest efficiencies were 0.57% and 0.84%, respectively.

 

Research at Pomona