Drachenfels Mountain loomed ahead of Greg Stone ’05 and Chad Althouse, a sophomore at Penn State. As the two students bicycled toward the jagged hill, they recalled the hero Siegfried who, according to German legend, long ago battled a dragon to rescue a maiden on this mountain.
The students could not find the dragon’s den, but they explored the ruins of the Drachenfels Castle and admired the German countryside.
Stone and Althouse studied one month last summer at the University of Bonn through an exchange program that involves four universities in the U.S. and Germany and is funded by the National Science Foundation
(NSF) and its German counterpart. Under the direction of Volkmar Dierolf
, an associate professor of physics at Lehigh, the students conducted research in nonlinear optics. They also worked with German graduate students and with Karsten Buse, a physics professor at the University of Bonn.
Although Stone and Althouse were busy during the day, they spent their weekends as tourists, borrowing bikes and traveling through cobblestone streets “like Europeans,” says Stone. They rode their bikes down the Rhine, visited a park in Bonn and toured the nearby city of Cologne, in addition to their visit to Drachenfels.
Neither Stone nor Althouse spoke German, so they relied on students at Bonn who could speak English and on a few phrases they had learned to navigate through the country.
Stone, who enjoys visiting new places, was “wide-eyed and amazed” on this, his first visit to Germany. Althouse also enjoyed the trip, despite suffering a collapsed lung two weeks into his stay. “It’s a beautiful city,” he says of Bonn.
Stone, who is now a Ph.D. candidate, worked with Dierolf, who is funded by the NSF, as an undergraduate doing research in non-linear optics. He studied the behavior of light as it passes through materials that convert light from one color to another.
Althouse studied with Dierolf as part of the NSF-funded
Research Experiences for Undergraduates
(REU) program in Lehigh’s physics department. REU students conduct hands-on research projects with professors at Lehigh. At the end of the 10-week program, students present their findings to fellow REU participants, professors and graduate students.
Stone had taken part in the REU program as an undergraduate in 2004.
In their research last summer, Stone and Althouse examined ferroelectric materials, which are characterized by a displacement of charged ions (positively and negatively charged particles), causing electric dipoles. “These dipoles are similar to little magnetic needle that can point in two distinct directions, like up or down,” Dierolf says. Regions where all the dipoles point in the same direction are called domains.
Investigating domain inversion
Optical physicists, like Dierolf and his students, are intrigued by a phenomenon called the domain inversion, which occurs when all the dipoles in a domain switch their direction simultaneously. Dierolf and Buse control these domain inversions with lasers that are fired at the crystal. Using different lasers, Stone and Althouse investigated domain inversion in two different materials: lithium niobate (LiNbO3), which Stone studied, and lithium tantalate (LiTaO3), which Althouse studied.
As an REU student, Stone developed a Raman tweezers for biological applications. Stone used the Raman tweezers like bathroom tweezers to grab and identify micrometer-sized components in the cell called organelles.
Raman tweezers use lasers to trap small glass beads. Like a ping-pong ball in a serving bowl, Stone says, glass beads that are farther from the center will feel a greater pull to the center. Particles in the center of the laser beam, like balls in the center of a bowl, remain at rest in the laser beam. When the laser is turned off, the glass beads once again float freely through the solution.
The labs where Stone and Althouse conducted their experiments are filled with items that could serve as props for the movie Star Trek
. A thick metal table floats on air pumped by a large compressor; the floating prevents sensitive equipment from being disturbed by vibrations. Bright green laser beams, fired through a maze of mirrors and lens, pass through the sample crystal. A charged coupled device (CCD) converts the light to electrons, which are then converted to a graph, and an optical luminescence microscope uses luminescence from the object to give more information about the material being studied.
In one experiment, they measured the Raman spectra, which show specific patterns, like fingerprints, of the crystal. From the spectra that Stone and Althouse measured in a high-resolution optical microscope they were able to identify the regions where the domains meet – an important finding considering that these regions are not easily visible. Understanding these regions will be important to creating better optical devices.
Before working with Dierolf, Althouse wanted to study nanotechnology after graduation. Now he is planning to apply to Lehigh to work towards an M.S. degree in Lehigh’s photonics program.
After completing his Ph.D., Stone hopes to become a researcher.