Current Experiments
Our primary area of research in the AMO physics lab is in photodetachment from negative ions. Photodetachment is a process (somewhat analogous to the the photoelectric effect) in which a negative ion absorbs one or more photons and subsequently ejects its extra electron. Photodetachment studies have applications in atmospheric science, plasma physics, astrophysics and other areas. This subfield of AMO physics also gives us insight into electron correlations - which are responsible for covalent bonds. We are particularly interested in photodetachment in the presence of external electric and magnetic fields. As it turns out, a negative ion undergoing detachment in an external field behaves as a single-atom interferometer! For a general introduction which describes some of our work, you can download a PowerPoint presentation made to a local chapter of the Optical Society of America.
Current and recent projects include the following:
Photodetachment spectroscopy of the O- ion: This work yielded a new value for the electron affinity of the O atom, and has corroborated results from a 1997 time-domain experiment. This work was published in Physical Review A. Download this article.
Photodetachment in combined, parallel electric and magnetic fields: This work developed into an international collaboration with theorists working in Germany and Canada, and has been recognized as the first experiment ever to probe detachment in combined fields. Our experimental results and theory show qualitative agreement. This work was published in Physical Review A. Download this article. Also, you can download a PowerPoint poster presented on this work at DAMOP 2001.
Relative strengths of Zeeman transitions in photodetachment in a magnetic field: We have measured the relative strength of the first Zeeman transition in detachment from O- and S-. This work was published in Physical Review A. Download this article, or download a recent poster on this work presented by Anders Langworthy '04 at a meeting of the Southeastern Section of the American Physical Society.
Evaporative cooling from a Penning ion trap: this work involves a simple cooling process analogous to the way in which a cup of hot coffee cools itself: the hottest atoms escape the container first, leaving behind a cooler, smaller sample. The primary result is that subsequent experiments can be conducted with diminished Doppler broadening effects. The prospect of exploiting this technique in the AMO lab opens endless experimental opportunities. We are working to optimize the cooling process, using new instrumentation-control code written in LabVIEW.
Photodetachment spectroscopy at the lowest energy threshold: This goal of this new project is to measure the spin-orbit splitting in both S- and O- and to make the first-ever observation of magnetic structure at the lowest energy detachment threshold.
Laser Tweezers: We are also currently engaged in an interdisciplinary project using a set of optical tweezers. These are also often known as laser tweezers. The apparatus can be used to trap and manipulate small objects held in an aqueous solution - from tiny polystyrene balls to single cell organisms and even DNA strands! The laser tweezers were constructed during the summer of 2003 by Rachel McCord '04, as part of Rachel's bio-physics major. We are currently calibrating the optical tweezer force, and studying motility of the unicellular green alga Chlamydomonas. For more details, download a PowerPoint presentation given by Rachel, or a poster given by Rachel at a meeting of the Southeastern Section of the American Physical Society (this poster won 2nd place for the Marsh White Award given each year for an undergraduate poster). Rachel's work was published in Cell Motility and the Cytoskeleton. This interdisciplinary project is a collaboration with Dr. Karen Bernd of the Davidson College Biology Department, and with Dr. William Guilford of the University of Virginia Department of BioMedical Engineering. It has been supported by funds from the Duke Foundation, the Howard Hughes Medical Institute, and the Davidson College Vice President for Academic Affairs Office. Check here for a college relations article on this project. We look forward to future collaborations with cell biologists and others interested in the apparatus.