Department of Physics
SCHEDULED EVENTS (2009-10)
OTHER IMPORTANT DATES
Note that what used to be the morning part of the GRE examination (the general part) is no longer given in paper format. It is available only at computer sites, the nearest two of which for Lawrence are in Oshkosh and Stevens Point. The examinations are administered at almost all times on a first-come first-served basis. If you are planning to take this examination this fall, you must register to reserve a time. October is a good month to take the general examination so that, later in the term (see later item), you can focus on the subject area examination, which is given as a paper and pencil examination. Further information about the GRE can be found at http://www.gre.org.
Dr. Baer, a major contributor to laser physics and various applications thereof, will discuss the 50-year history and impact of the laser first demonstrated by Theodore Maiman of Hughes Aircraft in 1960. Dr. Baer is one of Lawrences most accomplished physics graduates. Prior to joining Stanford, he was founder of Arcturus Bioscience, Inc. In 1996, where he served as the company's Chairman and CEO until 2005. Prior to Arcturus, Dr. Baer was Vice President of Research at Biometric Imaging, where he led an interdisciplinary group developing applications in the areas of AIDS monitoring, bone marrow transplant therapy, and blood supply quality control. From 1981-1992, Dr. Baer was at Spectra-Physics, Inc., where he held positions as a Research Scientist, Spectra-Physics Fellow, and Vice-President of Research. In 1989 he co-founded a new company, Spectra-Physics Laser Diode Systems, which was established to commercialize diode and solid-state laser instruments. Dr. Baer has been a pioneer in many areas of biotechnology, laser development, and laser applications, and is listed as an inventor on over 60 patents. He graduated with a B.A. in physics from Lawrence, magna cum laude, and received his M.S. and Ph.D. in atomic physics from the University of Chicago. He is a fellow in several international scientific societies.
Town Meeting of the Entire Physics Department
The purpose of this meeting is to discuss various matters of concern to students and faculty, e.g., key card access to departmental spaces, machine shop and laboratory policies, summer research programs, physics colloquia, GRE, SPS, WOP, APS, LPW, Bjorklunden, letters of recommendation, the Senior Capstone program, ... All physics majors are expected to attend this meeting.
Rob Niederriter, LU '10
Fluctuations and Transport in the Enormous Toroidal Plasma Device at UCLA
Turbulence and transport across magnetic field lines disrupt plasma confinement, which is particularly troublesome in toroidal geometries potentially useful for fusion energy. We investigate fluctuations of a helium plasma in the Enormous Toroidal Plasma Device (ETPD) at UCLA using 4-tip Langmuir probes to measure potential and ion saturation current. ETPD is a simply magnetized torus with major radius 5 m. The torioial vacuum chamber has a rectangular cross section that is 3 m tall and 2 m wide. Plasma is generated by a lanthanum hexaboride (LaB6) cathode discharge into a helical magnetic field produced by an approximately 200 G toroidal field and an approximately 6 G vertical field. Typical plasma density is ne about 1013 cm-3 and typical electron temperatues it Te about 10-20 eV. Increasing neutral pressure narrows measured plasma density cross-sections, implying pressure dependence of cross-field transport. Observed fluctuations show drift and interchange instabilities. The intensities of drift and interchange instabilities vary with neutral pressure, which possibly contributes to the observed changes in transport. This talk reports on work done in an REU project at UCLA during the summer of 2009.
Allyssa Stephenson
EIT with a Noisy Laser
Electromagnetically induced Transparency (EIT) is a quantum mechanical phenomenon in which light passes through an otherwise opaque material. EIT has applications in slow light, quantum memmory, and fiber optical communication. Our research uses noise spectroscopy to find ideal parameters for enabling EIT in Rubidium vapor, specifically focusing on the effects of laser beam power. This talk reports on work done in an REU project conducted at Lawrence University during the summer of 2009 and supervised by Professor Shannon O'Leary.
Dr. Orozco will be on campus all day Wednesday and until 4:00 PM or so on Thursday. Check with Professor Brandenberger to make appointments to chat with him or join him for lunch. DDr. orozco will give two talks during his visit:
We 28 Oct 7:30 PM Y-121: Thomas A. Steitz Hall of Science Colloquium
Waves and Particles of Light
Professor Orozco will review the long and tangled history of the nature of light. Isaac Newton thought light was corpuscular; Thomas Young and Clark Maxwell and most 19-th century physicists believed light to be wavelike; Max Planck, Albert Einstein, and numerous other 20-th century physicists concluded that light can behave as either a particle or wave. Professor Orozco, an expert on the way that radiation interacts with matter, will shed his own light on this topic---one of the richest topics in all of physics. A Distinguished Traveling Lecturer for the Division of Laser Science of the American Physical Society, Dr. Orozco is eminently qualified to discuss this subject with a general audience.
Th 29 Oct 11:10 AM Y-115: Physics Colloquium
Quantum Optics and Cavity QED
Professor Orozco will discuss his current research program involving atoms that pass through optical cavities within which only a few photons are trapped, or stronger beams of photons that pass through a trap that contains only a few atoms. Professor Orozco, an expert on these matters and quantum optics, will discuss these topics, which are a major interest in contemporary atomic and optical physics. A Distinguished Traveling Lecturer for the Division of Laser Science of the American Physical Society, Dr. Orozco will discuss these areas at a level understandable by undergraduates. Dr. Oozco supervised the Ph.D. work of Lawrence physics graduates Stephen Mielke, LU '92, and Wade Smith, LU, '98.
Simulating Polydisperse Materials with Distributions of Debye
Marie Milne, LU '10
The Cole-Cole model has been shown as an excellent approximation to true polydisperse materials; however, simulations of this model are difficult. Thus I investigate using distributions of the simpler Debye model represented by the method of polynomial chaos, to approximate multi-pole materials in a more computationally feasible way. This talk reports on work done during the summer of 2009 in an REU program at Oregon State.
Computational Modeling of Astrophysical Hydrodynamic Systems
Brad Bodee, LU '11, and Joe O'Halloran, LU '10
The origin of gas giant planets like Jupiter is greatly disputed. Observational data to date show the existence of 403 (up from 358 in August) exoplanets---planets which are not in our solar system, most of which are probably Jupiter-like. We use a 3-D hydrodynamics program to study one of the proposed planet forming mechanisms: the disc instability model, in which a gas planet is formed via interactions of spiral arms in a gravitationally unstable circumstellar disc of gas and dust. We know that most young, planet forming systems---including our own---are exposed to a variety of environmental factors such as the presence of a companion or star cluster. However, the vast majority of work by computational astrophysics groups assumes instead that such a disk is in a closed system consisting of only the disk and the star it surrounds,. This summer, our group has altered a state of the art solar system simulator to address this deficiency. We have focused on removing the commonly used assumption of vertical symmetry, with the goal of adding simulated companions or other perturbers as orbiting point masses. This will allow warping and vertically asymmetric heating and cooling. In today's talk, we will present results of our additions to the code. This talk reports on work done at Lawrence during the summer of 2009 and supervised by Professor Megan Pickett.
EE or Applied Physicist? An Electrical Engineer's Journey Through Plasma Physics, RF, and Photonics
Kenneth A. Connor, Professor, Rensselaer Polytechnic Institute
An Investigation of the Gait of Kinesin
Julia Ziege, LU '10
Ion Traps: Techniques and Applications
Joan Marler, Northwestern University
Charged particle traps offer an unprecedented level of control for the observation of quantum systems. Basically “infinite” confinement times and the almost complete isolation of particles inside these traps is essential for precision measurements on single quantum systems. Since the early days the techniques developed in the field of charged particle trapping have been appropriated by scientists in the fields of astronomy, fundamental particle physics, anti-matter science, quantum information science and more recently condensed matter physics. In this talk I will present the techniques for trapping and laser cooling of ions. Then I will present two applications in which I have been involved. The first involves clouds of ions which when trapped and laser cooled below a critical temperature, form a spatially ordered state, referred to as an ion Coulomb crystal. I will present the unique properties of these systems which make them a promising candidate for the realization of various quantum information devices, including quantum repeaters and quantum memories*. Then I will briefly touch on the goals of my current research group, to trap and laser cool molecular ions in the hopes of making precision measurements of possible changes in values of fundamental constants.
*Work performed in the group of Michael Drewsen at the University of Aarhus, Denmark.
Soliton Propagation in Nonlinear Transmission Lines
Michael Treiman, LU '10
Solitons – self reinforcing waves with constant velocity, shape, and amplitude – are found in many wave media with dispersive and nonlinear effects. This work uses a nonlinear transmission line composed of inductors in series and nonlinear capacitors in parallel. Dispersion arises from the use of a series of discreet components. Conversion of any input pulse into solitons is explored – specifically, the conversion of low frequency energy to RF.
Optical Momentum and Angular Momentum: Understanding the Physics, and Applying Light for Micro-Mechanical Control in Systems
Professor Gabriel Spalding, Illinois Wesleyan University
For microfluidic, “lab-on-a-chip” technologies and for research involving biomedical imaging, the components of interest are small enough that even the relatively weak forces (and torques) associated with light can be sufficient for mechanical manipulation, and offer extraordinary position control, and can measure interactions with three orders of magnitude better resolution than atomic force microscopy. This talk will include a discussion of the underlying physics and will extend our understanding of the angular momentum carried by light to clarify what orbital angular momentum means in the “stationary states” encountered in quantum mechanics. The talk will also detail some of the considerations that go into designing optical systems appropriate to micromanipulation of different types of micro- and nano-scale samples (dielectric solids or fluids, metals, semiconductors). Advanced methods, including the use of holographically structured optical fields, will also be introduced.
Making Computers Play as Scientists and Musicians
David Meichle, LU '10
Computer programs for automatically determining the tempo, i.e. 'foot-tapping rate,' of musical audio signals are of widespread interest for applications including automated computer accompaniment, beat-synchronous music visualization, musical performance analysis research, and automatic song similarity computation and play-list generation. Our current research has developed a novel and simple, real-time algorithm for finding the tempo and beat locations in a digital audio file. Quantitative analysis of our algorithm shows results near state-of-the-art, with minimal implementation complexity and computational requirements. Current progress and directions for further work towards a robust system capable of following expressive tempo changes (rubato, ritard, accelerando) in real-time will be discussed.
This talk will also outline some of the broader goals and applications of the Music Information Retrieval (MIR) research, currently being done at the Austrian Research Institute for Artificial Intelligence's Music Processing Group in Vienna where this work was done in a six month research internship earlier this year. MIR could be of interest to the general computing, engineering, music production, scientific and musician audience. This talk will be technical, but the fundamental ideas and applications will be accessible for a general audience of scientists or musicians.
Darren Williams, PhD
Associate Professor of Physics and Astronomy
Penn State Erie, The Behrend College
“The Origin of the Moon and Other Planetary Satellites”
The Moon is one of the largest planetary satellites in the Solar System compared to its planet. How the Moon formed is a longstanding mystery, although most astronomers think it was born from a cosmic catastrophe, a chance collision between a Mars–sized protoplanet and the infant Earth. Other Solar System satellites formed differently; many accumulated slowly out of rings of debris encircling the gas giant planets, while others were snared by their planet’s gravity. Local examples of small satellites formed through capture suggests that moons the size of Earth could be commonplace around nearby stars.
Darren Williams, PhD
Associate Professor of Physics and Astronomy
Penn State Erie, The Behrend College
"The Search for Habitable Planets"
Astronomers have now discovered hundreds of planets in orbit around nearby stars. Most have not been photographed and are only known from a star’s subtle movement in response to the planet’s gravity. However, some of the planets are small enough to be made of solid materials like the Earth, and astronomers will one day be able to observe these planets directly and determine whether they harbor life. In tonight’s Shapley lecture, Dr. Williams will discuss what is known, and what can be known about extrasolar planets, as well as the prospects for finding another habitable Earth with liquid water in the near future.
Robert Niederriter ('10)
"Bright Lights, Big Toys, & High Voltage: Status of the Lawrence University Plasma Physics Lab"
Plasma is strange to us earthlings, yet it makes up most of the universe. In the lab, we can create plasma using DC high voltage or by shooting electrons at a neutral gas. Two new plasma experiments are under development at Lawrence University and will be described in this talk. We plan to use electrostatic Langmuir probes as our main diagnostic to measure three important properties of our plasmas - density, potential, and temperature - these quantities tell us what the plasma is doing. Plasma waves propagate through long-range electromagnetic interactions rather than collisions between individual particles: in contrast to sound waves in air, for example. We plan to measure the properties of plasma waves in the lab. Starting next spring, the plasma physics course will include a laboratory component using a new plasma device dedicated to that course and student research. This talk will include an update on progress toward development of this apparatus.
Photo Shoot: 4:15 PM (promptly) near the front entrance of the Warch Campus Center. Faculty members, seniors, and juniors leaving for engineering schools should meet for the taking of this traditional photo.
Gennady Malyshev ('10)
"Three photon excitation as a potential explanation for signal inversion in a DROP spectrum"
This work explores a possible explanation for an unexpected signal inversion in a Double Resonance Optical Pumping (DROP) spectrum of Rubidium. The proposed explanation considers two mechanisms of excitation of atoms from a ground state by way of three lasers. One of these mechanisms is the familiar three-step excitation, driving atoms step-by-step up an energy level ladder, while the second is an uncommon three-photon excitation which drives atoms directly to the third excited state. This three-photon absorption is a plausible candidate for the cause of the inverted signal, and a computer model of these excitations has produced spectra similar to the experimental results that motivate the work.
Michael Treiman ('10)
"Quasicrystals"
Quasicrystals are crystal-like structures which exhibit long range symmetrical order, though unlike crystals, without periodicity or strict symmetry. Diffraction from quasicrystals results in a pattern similar to crystal diffraction. While periodic crystals are restricted to either three-fold, four-fold, or six-fold rotational symmetry, quasicrystals can be constructed with the forbidden five-fold and ten-fold symmetrical order. The Penrose tilings are an example of a simple quasicrystal tiling. We explore the diffraction symmetry of Penrose tilings and other quasicrystals in comparison to diffraction of more random tilings.
Annual Reception for physics graduates and their graduation guests. All those associated with the Department of Physics who happen to be in Appleton are invited.
Gathering for all physics majors and minors returning from reunion, providing an opportunity for those individuals to meet and greet both current and retired faculty members, learn of new initiatives in the Department, network with one another, and bring all attending up to date on their activities since graduation.