PSU Magazine Spring 1988

researchers who must control all fac– tors as precisely as possible in their experiments. The solution may be related to an enigma Casperson has studied for some time, a process termed laser light instability. "Some continuous beam lasersjust start blinking on their own," says Cas– person. "With study we hope to learn how to stop this behavior or in some cases how to predict and use it." Cas– person points out that when some las– ers become erratic, pulsing for no apparent reason, their average power level can increase. "We may want to encourage this," notes Casperson, "but the first step is understanding why it happens." Brown University engineering and physics professor Nabil Lawandy lauds Casperson's work in instabilities. "It's important to be able to predict behav– ior of a device in order to exploit it," he points out. "Casperson pioneered the realization that you could use equations to model what actually happened in a laser, to make theory and observation really match." C asperson first became interested in laser instabilities at the urging of a faculty advisor at the California Institute of Technology, which he attended after earning a B.S. in physics at MIT. He moved on to UCLA, where, soon after, he solved a type of laser instability. -..I guess you could call me the father of the Casperson Instability," he admits with some embarrassment. "I discovered it while working on my Ph.D thesis, kept thinking about it and running computer programs, and finally solved it." This is one of the many successes Casperson has had in his 21-year involvement with lasers. PSU School of Engineering and Applied Science Dean Chik Erzurumlu says Casper– son's prolific research is "at the cutting edge," attracting students from all parts of the United States. In 1984, the Institute of Electrical and Electronics Engineers awarded Casperson a Centennial Medal for "major contributions to the theory and applications of lasers and devotion to and continued excellence in electrical engineering instruction." A year later, Liquid nitrogen poured into the lab's Xenon laser regulates gas pressure -- the lower the pressure the more energy produced. Casperson won one of ten Faculty Excellence Awards given by the Oregon State System of Higher Educa– tion, and he is listed in numerous Who's Whos. Casperson's success goes beyond instability theory and awards to include his original design and build– ing of a round laser, the first of its kind. The laser, shaped like a flying saucer with short pillars sprouting from its top, rests casually beneath a lab bench. Casperson handles his creation with affection. "This is a carbon dioxide laser with the mirror wrapping all the way around inside," he explains. "It's com– pact and relatively efficient, but no one has found a use for it yet," a hint of regret in his tone. Casperson is not discouraged. The shape or geometry of lasers is extremely important and he works with his students on experiments in this field. The traditional longitudinal laser, a tube with mirrors at each end, makes poor use of energy. The argon laser Macfarlane works with has just .01 percent efficiency; the heat of wasted energy is carried away by run– ning water. Even the conventional carbon dioxide laser - used in indus– trial welding because it packs a con– centrated punch into a relatively small package - can deliver as light only 20 percent of the energy that goes into it. PSU MAGAZINE PAGE6 Fahad Al-Mashaabi, another of Casperson's students, recently built a more compact and rugged version of the C02 laser, in which the electrical current used to excite the gas atoms intersects with the light inside the laser at a right angle. Such improve– ments, and other experiments with mirror shape and design, may ulti– mately increase efficiency and reduce operational cost, making the device even more widely useful. The usefulness of lasers is most apparent in the field of communica– tions. Transmitting signals over glass fibers has proven much more efficient and less expensive than conventional electronic communication. Casper– son's students have set up a communi– cations laser demonstration for the many interest groups that tour the lab. A loudspeaker with an ordinary drinking straw attached sits in front of a helium-neon laser. As the speaker vibrates with sound the straw moves in and out of the laser's light beam. This movement is imperceptable to our eyes but easily recorded by a photo cell which converts the movement into electrical signals read by another pair of stereo speakers. Viola! Sound carried by light, anal– ogous to methods increasingly preval– ent in long distance phone transmis– sion over glass fibered cables. Several of Caspersons' students, Anthony Tovar and Bahram Zandio, are developing tapered fiber couplers to hook different size fibers together without losing any of the information being transmitted - a serious need in the fiber optics industry. Such immediate applicability is not always the case in the PSU laser lab, where research is often a long step ahead of practical use. For Casperson, the chance to solve a mystery is enough. "If we can better understand the laser itself," he says, "Then we'll know best how to use it." And people around the world will continue to benefit from the exploration and per– fection of those early theories Albert Einstein called "splendid light." PSU (Joli A. Sandoz is a free-lance writer and a 1974 graduate of Portland State.)