Research at Hendrix

Robert W. Dunn

Professor of Physics and Senior Research Fellow

Ph.D., University of New Mexico

Research interest: Hendrix College Ring Laser Undergraduate Research Project

The ongoing Hendrix College Ring Laser Undergraduate Research Project uses large ring laser interferometers to measure geophysical phenomenon. Currently, students under the direction of Professor Bob Dunn are using ring lasers to study seismic waves from the Guy, Arkansas earthquake swarm and infrasound emissions from hurricanes and volcanoes. Infrasound consists of very low frequency acoustic waves that can travel around the world with minimal attenuation. Students have participated in constructing the ring lasers, designing the signal detection systems, and reducing the data.

In an active ring laser interferometer, coherent waves of light are propagated simultaneously around the laser cavity in both a clockwise and counterclockwise direction. If the laser cavity is rotating, the time for light to propagate around the cavity depends on its direction of propagation. Since the light source (plasma tube) is inside the cavity, the difference in transit time creates a frequency difference between the two counter propagating beams. A relatively small amount of light from both of the bi-directional waves will leak through the dielectric cavity mirrors. The transmitted portions of the bi-directional waves can be collimated and combined on an optical detector. Earth's rotation can create a beat frequency proportional to the rotation rate. If the laser cavity is perturbed by phenomenon such as seismic waves or infrasound, the beat note is frequency modulated and the frequency modulation side band contain the signatures of the perturbing phenomenon.