Department of Physics
SCHEDULED EVENTS (2006-07)
OTHER IMPORTANT DATES
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., colloquia, GRE, SPS, WOP, APS, LPW, Bjorklunden, letters of recommendation, the Senior Capstone program, ... All physics majors are expected to attend this meeting.
Note that the morning part of the GRE examination 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, come December (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.
Photoluminescence of ZnO and MgZnO Nanoparticles
Russell Geisthardt, LU '08
ZnO and MgZnO nanoparticles are promising materials for use as ultraviolet light-emitting materials. When we alloy ZnO with MgO, it creates a family of tunable, wide-bandgap semiconductors. My research this summer at the University of Idaho focused specifically on the behaviors of these materials under low temperatures. The study of these materials at low temperatures allowed us to better understand the mechanisms behind their light-emitting properties, as well as to open the door for low-temperature applications of these materials.
Spin Transport in Ferromagnet-Semiconductor Heterostructures
Claire Weiss, LU '07
Spin transport is an important area of research in physics because it could lead to a deeper understanding of fundamental processes in physics (such as electron tunneling through a barrier) and because its applications could be useful in creating new types of electronic devices in which both charge and spin could be mainpulated. Spin transport of charge carriers across a potential barrier is studied here in several different samples. The samples are all ferromagnet-semiconductor heterostructures. An external cavity tunable diode laser was used to send polarized light into the heterostructures. The current through a quantum well was then measured to study the effectiveness of spin transport of the charge carriers. Although we did not observe spin ejection by these methods, we did observe electro-absorption, Zeeman splitting, and Landau diamagnetism, which indicate that spins were produced in the quantum well and this gives us hope for future spin ejection experiments. This talk reports on work done in an REU program at the University of Minnesota during the summer of 2006.
Fast Photoinduced Refractive Index Modulation in Chalcogenide Glass
Annemarie Exarhos, LU '07
The nanosecond time dynamics of the non-linear refractive index of chalcogenide glass will be presented. Observation of the dynamics is achieved by intersecting pulsed laser beams at 532 nm to create an intensity grating in the material. This volumetric grating induces an index of refraction change whose structural transformations are present even after the excitation pulses have crossed. The relaxation time of the non-linear index of refraction is 35+/-1 ns and is independent of the intensity and polarization of the excitation pulses. Diffraction efficiency data provides a value of 1.15E-11 cm^2/W for the non-linear refractive index. This research was funded by the NSF-REU Program at Lehigh University during the summer of 2006.
The 3-2 Engineering Program at Washington University
Mr. Paul Groszewski,
Dual Degree Program representative from
Washington University, St. Louis, MO
Following the two talks on summer experiences, Mr. Groszewski will discuss Lawrence's affiliation with Washington University in a program that makes engineering available to Lawrence students.
A Kilogauss-scale, High-vacuum Toroidal Electron Plasma Experiment
Julian Hector, LU '08
The Lawrence Non-neutral Torus II (LNT II) is a new experiment nearing completion that will trap electron plasmas in a toroidal magnetic field. This device will also be used to study the reasons for particle loss, the requirements for a stable equilibrium, and the dynamics of a complex system which exhibits collective effects (e.g., waves, instabilities, turbulence). Utilizing a 1 kG magnetic field, a base vacuum pressure on the order of 10E-9 Torr, and precisely machined gold-plated boundary electrodes, the LNT II is expected to produce a confinement time of one second, twenty-five times longer than previous experiments. Longer confinement times will permit the study of slower processes that lead to particle losses. This talk reports on a research project undertaken in the summer of 2006 under the direction of Professors Matthew Stoneking and Joan Marler.
Automated Data Acquisition for an Electron Plasma Experiment
Sarah Curry, LU '08
A new experiment, nearing completion, will confine an electron plasma in a toroidal magnetic field. Trapped electron plasmas can be used to study the equilibrium, stability, and dynamics of a complex system that exhibits collective effects. The image charge signal on the segmented, grounded, conducting "wall probes" that form the boundary for the plasma will be used to observe fundamental modes of plasma oscillation. More information about these unstable oscillatiions is desired to achieve a stable plasma. This talk will describe the data acquisition system for the new experiment. LabVIEW programs have been designed to acquire data from wall probes. The design enables users to direct oscilloscopes through LabVIEW, and convert the acquired data sets from each wall probe into a text file of 25,000 coordinates. This information makes it possible to compare data sets from different wall probes and different trials. This talk reports on a research project undertaken in the summer of 2006 under the direction of Professors Matthew Stoneking and Joan Marler.
Experiments Using MOTRIMS Technique
Dr. Brett DePaola, Department of Physics, Kansas State University
MOTRIMS, which stands for "magneto-optical trap recoil ion momentum spectroscopy", represents a variation on the more common COLTRIMS technique. MOTRIMS is proving to be superior to its forerunner technique because it offers greater breadth and experimental flexibility. Professor DePaola will discuss informally the essence of the approach and several of its applications. The three letters MOT in MOTRIMS indicate that this type of spectroscopy embraces the magneto-optical trapping approach that is being developed at Lawrence.
Confessions of a Pluto Hater
Dr. Megan K. Pickett, Department of Physics, Lawrence University
On August of this year, the International Astronomical Union (IAU)---the governing body of astronomers and astrophysicists responsible for classifying and naming celestial objects---changed the status of Pluto from planet to "dwarf planet". The decision to reclassify Pluto (as well as its moon Charon and two other objects---former asteroid Ceres and formerly unclassified Eris) follows decades of sometimes passionate debate in the astronomical community regarding this tiny, odd world. Some hailed the reclassification as a "triumph of rationality over sentimentality"; others argued that the new classificatiion made little sense, or was too vague, or was just plain mean.
As a professional astrophysicist and a planetary scientist, I have argued for some time that Pluto should not be considered a planet, at least not at the same level or class as the other eight in our Solar System. I admit it: I am a Pluto-Hater. In my talk, I will discuss what we know about Pluto and its moon Charon, the debate surrounding Pluto's status, and why the new convention both makes sense and in the end doesn't really matter.
Numerical Modeling of an Electron Plasma
Bao Ha, LU '07
A new toroidal electron plasma apparatus is coming online in the basement of Youngchild Hall: the Lawrence Non-neutral Torus II (LNT II). The primary means of diagnosing the plasma will be the measurement of image charge induced on gold-plated electrodes. Numerical modeling methods are employed to solve Poisson's equation in toroidal geometry and determine the image charge on the wall sections. The calculated electric field at the center of the plasma is used to determine the ExB drift velocity and, consequently, the trajectory of the plasma. The numerical model will be used to extract properties of the plasma from experimental data obtained in the LNT II device. This talk will report on a capstone project directed by Professors Stoneking and Marler that was begun in the summer of 2006 and continued in the fall term of 2006--07.
Non-Contact Atomic Force Microscopy of Liquid Crystal Films
Christopher J.~Hawley, LU '07
The surfaces of freely suspended thick films of 7O.7 in modulated crystalline-B phases have been imaged using non-contact mode atomic force microscopy. Large-scale images show 2.75 nm steps at the edges of layers on the surface of thick films that are adjacent to large flat areas. Previous models of x-ray diffraction measurements indicate that some of the crystalline-B phases of 7O.7 have static modulations with amplitudes of 0.7 nm and a period of about 10 nm. No surface modulations are seen, suggesting that the surface structure differs from that of the bulk modulation. A smectic-F structure is consistent with the observations.
The Pedestrian's Guide to Laser Cooling and Trapping
Annemarioe L. Exarhos LU '07
Atoms can be trapped in large quantities for long periods of time through the combined processes of laser cooling and magneto-optical trapping using an inhomogeneous magnetic field. These processes serve to slow down atoms with various velocities (and thus cool them to temperatures as low as 1 uK), confining them to a specific trapping region for up to several seconds in what is called a magneto-optical trap (MOT). The construction of such a MOT is currently underway at Lawrence University with rubidium, where we hope to use this trapping technique to further study and characterize the atoms.
In vestigating Mantle Flow at Tectonic Corners using Seismic Methods
Mark Growdon, LU '04, currently graduate student at the University of
Indiana
The measurement and interpretation of anisotropy, or directionally dependent material properties, is essential for studying plate tectonic theory, since anisotropy is linked to the current and past deformational processes in the Earth's crust and upper mantle. I used seismic waves to investigate anisotropy in two areas of the world: 1) the triple juncture of the Caribbean, North American, and South American plates as seen mainly in Venezuela and 2) the juncture of the Pacific and North American plates as seen in SE Alaska. Both of these regions have complicated interactions due to the multiple subduction environments that range from perpendicular to highly oblique motions at the plate boundaries. Due to the complex environment, there is not necessarily any reason to believe that there should be continuity across the whole region. However, by characterizing the anisotropy, we will gain insight into the amount and consistenty of deformation in these regions which may, in some cases, lead to interpretations about mantle flow.
Searching for Alien Life, Near and Far
Dr. Margaret C. Turnbull, Space Telescope Science Institute
Where in the universe might habitable planets, and perhaps life as we know it, exist? How will we recognize it when we see it? What can we do in the near term to try and find that out? This talk will review the information we have on hand now, the current situation regarding real missions to search for habitable planets and life, and present some ideas of how we can continue to move forward in the quest to find habitable planets orbiting other stars. NASA's current plans to establish a human presence on our nearest celestial neighbor may not be primarily motivated by science, but the search for life in the cosmos is a study that fits in harmoniously with many other exploration efforts. Can planet- and life-hunters be successful "hitch-hikers" on the road to the moon?
A Book Review on Information: The New Language of Science by
Hans Christian von Baeyer
Dr. Joan P. Marler, Lawrence University Department of Physics
I suppose that all of you (or at least most of you) have come to Lawrence to learn some information. I will attempt to analyze the origin of the word---and where else to start but with Plato's concept of Forms. In a classical sense, perhaps the best fundamental unit of information is encapsulated in the bit (1 or 0, i.e., the answer to a yes-no question). Quantum mechanics, however, introduces the qubit (1 and 0) as the (pre-observation) fundamental unit. I will discuss some of the implications of the qubit and reflect on how these two units, the bit and the qubit, are inextricably related via our participation in the world.
So Many DynamosBrandon Rice, LU '07
The magnetic field of Earth arises from self-maintained dynamos in the fluid outer core of Earth. Simplified laboratory simulations at the University of Wisconsin--Madison. This study, conducted as a senior capstone project under the direction of Professor Stoneking, attempted to simulate this behavior with an elaborate computer program.
Photo Shoot: 4:15 PM (promptly) on the steps on the west side of Downer Commons. Faculty members, seniors, and juniors leaving for engineering schools should meet on the steps for the taking of this traditional photo.
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.