Telephone: (507) 786-3619
Office: Regents Hall 276
I have been a member of the St. Olaf faculty since 1979. My research interests are in atomic and molecular physics, and over the years have included work on atomic collisions, multiphoton laser spectroscopy, radiofrequency hyperfine spectroscopy (in collaboration Physics Professor Emeritus James Cederberg) and measurement of atomic transition probabilities and excited state lifetimes. Here is my CV.
Recent Research Projects: In collaboration with scientists James Lawler at the University of Wisconsin and John Curry at NIST, I have been working on measurement of transition probablities for spectral lines in atomic cerium, whose spectrum is of current interest for astrophysical applications and product development in the lighting industry. Analyzing radiometrically calibrated spectra recorded using the large Fourier Transform Spectrometers at Kitt Peak National Observatory and at NIST/Gaithersburg, my students and I are working to expand the set of known transition probabilities in cerium by several thousand lines.
Here is a .pdf file of a poster presented at a recent meeting the American Physical Society's Division of Atomic, Molecular, and Optical Physics. It describes the measurement of almost 3000 transition probabilities in Ce I using known excited state lifetimes and our measured branching fractions for the allowed decay channels. This work was published in 2010 (Lawler et. al., J. Phys. B: At. Mol. Opt. Phys. 43, (2010), 085701).
Here is a .pdf file of a poster presented by students Gus DeMann and Warren Shull at the 2011 St. Olaf Summer Science Symposium and at the Midstates Undergraduate Science Symposium at the University of Chicago (November 4-5, 2011). It describes the analysis of relative populations of excited states in a discharge (using emission lines whose transition probabilities are known) and applying this information to measure new transition probabilities for lines from nearby levels. This built on work done by students Micah Buuck and Noah Mitchell in the summer of 2010.
Courses: In recent years I have been teaching Introductory Astronomy (Phys. 112), Musical Acoustics (Phys. 252), Principles of Physics II (Phys. 125), Maxwell's Equations (Phys. 375), Quantum Mechanics (Phys. 376) and the Advanced Laboratory Course for Seniors (Phys. 386). I enjoy developing computer-based resources as aids for learning in these courses. Here are a few sample animations, all in Windows .avi format:
Daily path of the Sun over the course of 1 year for an observer near Northfield, Minnesota (latitude 44.5 deg. N) (about 15 MB)
This animation plots the hour-by-hour location of the sun on successive days of the year (beginning with the vernal equinox) relative to the horizon plane of an observer near Northfield. The distorted figure-8 pattern (analemma) traced out by the daily variation of the sun's position at noon is highlighted - a consequence of the combined effects of the earth's tilt and variation of orbital speed. From this animation one can also see interesting patterns in the times of sunrise and sunset by thinking of the "circle of suns" plotted in the figure as markers on a 24 hour clock and noticing where the circle intersects the horizon plane on a given day of the year. This circle not only rises and falls with the seasons - producing the familiar increase and decrease in hours of daylight - but also rotates back and forth slowly as the noon sun moves around the analemma. Near the summer and winter solstices (sun at the top or bottom of the analemma) the circle's motion is almost entirely rotational - clockwise as you look at the screen - meaning that sunrise and sunset both shift toward later times of day for a brief period (roughly June 15 - 26 in summer, Dec. 9 - Jan 2 in winter) before resuming their more "normal" pattern of moving in opposition.
Normal modes of vibration of an idealized two-dimensional membrane (about 6 MB each):
(1) Fundamental (2) Mode with one nodal diameter (3) Mode with one nodal circle (4) Mode with one nodal diameter and one nodal circle
Motion of free particle wave packets (about 2 MB each):
Collision of a free particle with a potential energy barrier, illustrating the concept of "tunneling."
Collision of a free particle with a pair of barriers, illustrating the concept of a "collision resonance."
In this pair of animations, the free particle is represented by a Gaussian-distributed linear combination of momenta in accordance with the uncertainty principle. The peak momemtum corresponds to a kinetic energy of 60 units. Classically speaking, the particle would need a kinetic energy of 200 units to be able to get over the barriers, but in quantum mechanics the wave-like aspect of the particle yields a non-zero probability for particles of lower energy to cross the barrier (and in the second case, to get trapped between the barriers).