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Physics

The Power of Astronomical Adaptive Optics

Rachel Chin ('12); Daniel Contreras ('13); Lorcan McGonigle ('13); Blaine Gilbreth; *Scott Severson*; Mentor: Philip Choi
*Sonoma State University, Sonoma, CA

Abstract: The development of adaptive optics (AO) technology has made it possible for groundbased telescopes to overcome atmospheric distortion and achieve unprecedented image clarity. As the first step in a four-year plan to develop, fabricate and integrate an AO instrument for Pomona College’s 1-meter Table Mountain Telescope, we have designed a base optical system and assembled a laboratory AO testbed. We present here an overview of the project and projected timeline along with the current status of the instrument design and testbed development.
Funding Provided by: The Fletcher Jones Foundation (RC, DC, LM)

Development and Testing of Optical Components in an AO System

Daniel Contreras ('13); Rachel Chin ('12); Lorcan McGonigle ('13); William Gamber ('13); John Bremseth ('12 HMC); Blaine Gilbreth*; Scott Severson*; Mentor: Phillip Choi
*Sonoma State University, Sonoma, CA

Abstract: We present the development of an adaptive optics (AO) testbed instrument under construction for the Pomona College Table Mountain Observatory telescope. Our testbed is based on a micro-electromechanical system deformable mirror (MEMS DM), a piezo-electric tip-tilt-mirror, two Shack-Hartman wavefront sensors (WFS) and a Linux-based control software package. We first characterized the performance of the critical, active components of the system that will be integrated into the final closed-loop AO instrument and then used the testbed to validate the predicted performance of our instrument optical design. We have also demonstrated the ability to perform closed-loop wavefront corrections for static aberrations. The next step will be to introduce and correct dynamic aberrations in real time.
Funding provided by The Fletcher Jones Foundation (DC, RC, LM)

Characterization of bulk heterojunction P3HT:PCBM organic solar cells synthesized in open air

Jenna deBoisblanc ('11); Mentor: David Tanenbaum

Abstract: Organic photovoltaic (OPV) solar cells are a potential source of economically viable renewable energy due to low material costs and the possibility for large-scale, roll-to-roll manufacturing. One major drawback of OPVs is rapid cell degradation, especially in oxidizing environments. Synthesis in glove boxes is a common laboratory technique to improve cell stability; however, ambient processing is essential to keep down production costs. This experiment studied the performance and lifetimes of bulk heterojunction P3HT:PCBM organic solar cells synthesized in open air. PEDOT followed by the active material was spin coated onto ITO patterned substrates, and a CsF/Al evaporation created the back electrode. Characterization took place both indoors, using a Fostec lamp, and outdoors under direct sunlight. A LabView program and Keithley 2400 SourceMeter automated the data collection process. Efficiencies and fill factors reached up to 1% and 0.54 respectively. Within two hours of the initial test, cell performance decreased over 70%.
Funding provided by Pomona College SURP

Blazar Observation

Matt Hasling ('12); Mayra Amezcua ('12); Mentor: Alma Zook

Abstract: Blazars are Active Galactic Nuclei, and are some of the most violent objects in the universe. For this project, we monitored the radiation from a number of blazars in order to learn more about the properties of these objects, specifically about the magnetic fields that exist within the supermassive black holes at their centers. We worked with a number of different groups all over the country, watching different spectra of radiation.
Funding provided by The Fletcher Jones Foundation (MH), The Paul K. Richter and Evalyn E. Cook Richter Award (MA)

Computing Evaporative Cooling of Trapped Atoms

Zack Lasner ('12); Eric Dodds ('12); Joel Shuman ('11); Mentor: Dwight Whitaker

Abstract: We have computed the evaporative cooling trajectory for a gas of trapped atoms. The evaporative cooling process is important for creating Bose-Einstein condensates, an exotic state of matter that occurs at extremely low temperatures (~100 nanoKelvin). We improve upon previous models by including the atoms that have enough energy to escape the trap, but are in a state that does not escape. There are many such high-energy atoms in shallow traps, but almost none in very deep traps. Our model can therefore be applied to a broader class of traps than some previous models. We compare the cooling process in spherically symmetric harmonic (parabolic) and Gaussian trapping potentials at a variety of trap depths. For both trap shapes, shallow traps cool more efficiently, but they are not able to contain as many atoms to begin with. Shallow harmonic traps produce much more efficient cooling than comparable Gaussian traps.
Funding provided by The Fletcher Jones Foundation (ZL, JS)

Designing a Base Optics System in Preparation for KAPAO

Lorcan McGonigle ('13); Rachel Chin ('12); Scott Severson*; Mentor: Philip Choi
*Sonoma State University, Sonoma, CA

Abstract: This summer we designed an effective base system for an adaptive optics (AO) system on Pomona’s 1-meter telescope at the Table Mountain Observatory. With only a naïve, psilosophical knowledge of optics at the outset of our endeavor, we also aimed to better understand the basis of optics through its applications in optical design and in Zemax, our optical design software. Having tested each component individually to determine its optimal specifications and configurations, we developed our final model. Our final model used two pairs Off-Axis Parabolas to collimate and focus light without introducing significant aberrations into our final image. Moreover, when our system was optimized, aligned, and toleranced, it produced foci under 12 microns in radius and achieved all of our other requirements.
Funding provided by The Fletcher Jones Foundation (LM, RC)

Patterned Supported Lipid Bilayers Using Microcontact Printing

William Morrison ('12); Robert (Tewei) Luo ('11); Mentor: Alfred S. Kwok

Abstract: We have used patterned PDMS (polydimethilsyoxane) stamps to remove micronscale features from supported lipid bilayers with the process of blotting. The creation of consistent, high-quality patterns is difficult, and we have isolated several factors which influence the effectiveness and consistency of the transfer, such as pressure, initial contact, and size of the features. Our results also suggest that good lipid transfer only occurs on the micron-scale; featureless stamps will not consistently remove or deposit lipids.
Funding provided by The Fletcher Jones Foundation (TL)

Fourier-Transform Microwave Spectroscopy of the PbF Radical

Benjamin Murphy ('13); Alex Baum ('10); Mentor: Richard Mawhorter

Abstract: This project examined the rotational-energy spectra of the lead-fluoride molecule (PbF). Using microwave spectroscopy, we observed 70 rotational spectral lines between 3 and 26.5 Gigahertz for 208Pb19F, 207Pb19F, 206Pb19F, and 204Pb19F. Using this data, we determined the set of constants that describe the molecular structure of these four PbF isotopologues. As a radical, PbF is sensitive to the Zeeman effect, wherein external magnetic fields can cause the spectral lines to split. We used our measurements of the Zeeman effect for the strongest 208Pb19F and 207Pb19F transitions to obtain other valuable constants to help in our ultimate goal of using PbF to find the electron electric dipole moment (eEDM).
Funding provided by Pomona College SURP (BM, AB), Sontag Research Grant (BM)

Fabrication and Measurement of Suspended Carbon Nanotubes

Benjamin Pollard ('11); Dr. Shahal Ilani*; Avishai Benyamini*; Mentor: David Tanenbaum
*Condensed Matter Physics, Weizmann Institute of Science, Rehovot, Israel

Abstract: Carbon nanotubes (CNTs) are the subject of widespread continuing research for their unique mechanical and electrical properties. Researchers are experimenting with CNTs for use in everything from baseball bats to nextgeneration computers. Novel methods were used to fabricate CNT devices for measurement of fundamental quantum mechanical properties. For example, barriers along a nanotube can trap electrons between them, creating a quantum dot. Using external electric fields, the movement of electrons into and out of the dot can be controlled. The single-electron current that arises from this movement can be measured and compared to concrete theoretical predictions. In this project, nanotubes are suspended over trenches in a silicon substrate to isolate them electrically. A computer program was created to perform this procedure automatically. It will be used to quickly and reliably produce a variety of suspended nanotube devices that are immediately ready for experimentation.
Funding provided by The Kupcinet-Getz Science School for International and Israeli Students, Weizmann Institute of Science

Dipole Trapping to Achieve Bose-Einstein Condensation

Joel Shuman ('11); Zack Lasner ('12); Eric Dodds ('12); Mentor: Dwight Whitaker

Abstract: To create a Bose-Einstein Condensate (BEC), we cool Rubidium-87 atoms to nanoKelvin temperatures. Atoms are confined using near-resonant lasers and magnets in a magneto-optical trap, then loaded into a dipole trap where evaporative cooling can take place. Loading atoms into the dipole trap involves hitting a ~4mm diameter cloud of atoms with a ~30 micron, ~50 Watt, invisible CO2 laser in a vacuum; if the atoms are sufficiently cool and dense, they will be trapped in the electric field of this far-off-resonant light. This summer’s work has focused on optimizing loading conditions of the dipole trap, measuring properties of the cloud of atoms using absorption imaging, and characterizing the profile of the C02 laser.
Funding provided by The Fletcher Jones Foundation (JS, ZL, ED)

A Rolling Vortex Ring Gathers No Drag: Sphagnum, the exploding moss

Sam Strassman ('12); Andrew Cha ('13); Mentor: Dwight Whitaker

Abstract: Sphagnum, or common peat moss, is non-vascular and therefore does not grow higher than a couple millimeters. Its spores are easily be carried by normal air currents that occur 10 centimeters above the ground and higher. In order reach these heights, as Sphagnum dries out, it builds up pressure inside the pod (where the spores are located). Once it reaches pressures of between 3 and 5 Atm within the pod, the cap on top of the pod explodes off and a vortex ring is created, sending the spores as high as 15 centimeters. A vortex ring is a highly efficient way of moving one fluid through another, and without the vortex ring the spores would not be able to reach the necessary height. This summer we developed a model of this explosion using a computational fluid dynamics program called Fluent.

Photometry of Near Earth Asteroids

Catherine Wilka ('12); Alex Hagan ('10 HMC); Mentor: Bryan Penprase

Abstract: As collisions with some of our nearest neighbors have sparked global catastrophe and mass extinctions in the past, calculating the properties of potential intimate asteroid friends is of vital importance. This project is part of an international study of Near Earth Asteroids (NEOs). NEOs were imaged over the past year with PINTO, Pomona’s remotely operated telescope in New Mexico. The images were reduced and calibrated using pipelines scripted in the computer languages Python and IDL. We then performed photometry on these images, obtaining useable results for 28 nights from Fall 2009. These photometric results were entered into a final IDL pipeline, generating light curves of individual asteroids’ H magnitudes. H magnitude is the standard measure of asteroid brightness, and we will use our results to calculate the diameter of our observed NEOs in the future. The magnitudes and diameters will be entered into a database as standards for these objects.
Funding provided by The Fletcher Jones Foundation

Research at Pomona