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Pomona Students, Professor Publish Laser Tweezers Research in Professional Journal

Late last year, Pomona College students Perry Schiro, Class of 2004, and Christopher DuBois, Class of 2006, had their research on “Large capture-range of a single-beam gradient optical trap” published in Optics Express, a professional scientific journal produced by the Optical Society of America.

In layman’s terms, they used a single highly focused laser, like a very tiny Star Trek tractor beam, and found that the radius of the capture range was up to ten times the distance scientists previously thought it was. Schiro noted, “It's useful if you want to manipulate cells or other spherical objects non-intrusively.” Applications in molecular biology and other areas are possible. The paper was co-authored with Alfred Kwok, a professor of physics at Pomona.

Schiro, now a senior, first started working in Kwok’s lab the summer after his freshman year and built the original laser tweezers setup with little supervision. The next summer, Perry took the lead in the lab, continuing the work and making additions to the laser tweezers setup in Kwok’s absence. “I'm still picking up all the intricacies,” Kwok admits.

The potential of laser tweezers was first observed in 1986 by A. Ashkin et al. They discovered that when a tightly focused laser was aimed into a group of micron-sized (1 micron = 10-6 meters) glass or polystyrene beads suspended in a solvent, a bead will be drawn to and then trapped at the focal point of the laser. In order to understand why this works it is simplest to think of a marble rolling around in a bowl; the marble will eventually come to rest in the center of the bowl because that is where it will have the lowest potential energy. Similarly, the laser creates a capture-range where the lowest potential energy is at the focal point, so the beads are drawn there.

For over 15 years, it was thought that this capture-range was only efficient at a distance of about one bead-radius. However, during Schiro’s second summer, he and Kwok noticed that beads were being drawn in from significantly greater distances. In the summer of 2003, they decided to test this property. DuBois, then a freshman, joined the team, collecting data and brainstorming solutions to problems that would arise. “There's a lot of problem solving that goes on in the lab; it almost never work the way you want it to,” DuBois said.

Together, Schiro, DuBois and Kwok collected research showing that polystyrene beads roughly six to ten microns in diameter could be captured from an initial distance of approximately 100 microns from the trap-center. Their paper was published in the 15 December 2003 release of Optics Express. The full paper can be seen at under the archives.



Both Schiro and DuBois conducted their summer research with Kwok through Pomona College’s Summer Undergraduate Research Program (SURP). Each student in SURP is given $375/week for up to ten weeks of participation, and Pomona College pays for the professors’ lab equipment, which in this case was approximately $60,000 of tools, all state of the art. In the school spirit of promoting undergraduate research, Professor Kwok said, “I look for specific research projects that can involve students.”

Schiro, a physics major with a chemistry minor, comes from Marin County and attended The Branson School. He has played lacrosse for six years and is now captain of Pomona College’s state champion lacrosse team. His other sports interests include volleyball and soccer. He has applied to Stanford, Caltech, UCSB, and other renowned graduate schools and is still waiting to hear back from most. After obtaining his Ph.D., Perry plans to go into the scientific business industry but has not ruled out becoming a professor. His parents are Bob and Doreen Schiro, also residents of Marin County.

DuBois attended Jesuit High School in Portland, Oregon, and is in the process of deciding between a major in physics or mathematics. This summer, he will help Professor Ami Radunskaya develop computer programs to model tumor growth. His future may include graduate school, but for now he isn’t looking that far ahead. Formerly a cross-country runner, Chris has recently decided to take up biking, putting much of his summer research money into a new bike. He finished second in his first race. Chris’s other interests include camping, hiking, skateboarding, snowboarding, and the ever-popular college game, Beirut. His parents, Lloyd and Polly DuBois, are also residents of Portland.



Perry Schiro
Phone: (909) 607-2392

Christopher DuBois
Phone: (909) 607-5511

Alfred Kwok
Assistant Professor of Physics
Office Phone: (909) 621-8729