PSU Magazine Spring 1988

Amplification by Stimulated Emission of Radiation," explains what hap– pened. Atoms excited by light bursts or electrical jolts will, while returning to their normal resting state, give off light. Placed in an environment where this light energy can double back on itself -- say between two mirrors reflecting into each other -- the light increases in power and coherence. The coherence of laser light is what makes it unique. Ordinary light, pro– duced by the sun, a light bulb or can– dle, radiates outward in a multitude of waves traveling in all directions. Hold– ing a prism up to this light demon– strates the rainbow variety of wave– lengths present. But a laser using a particular gas, liquid or solid (such as ruby ions) as the source of light energy, produces light of a single color. The difference between ordinary light and that produced by a laser is the difference between the afternoon traffic noise around the Park Blocks and a single, crystalline note clear and penetrating enough to shatter glass. When directed by mirrors or other reflective devices, this pure light can be focused tightly enough to cut through sheets of steel, or drill a pin– hole through diamond. H .G. Wells imagined lasers in 1898 as a ray gun that could vaporize anything in its path. More recently, President Reagan has pushed the use of lasers in "Star Wars" weaponry. But, science fiction scenes of space duels and instant annihila– tion aside, destruction is not the most common laser use. Laser light reads price labels at the grocery store check– out counter, "plays" the music coded on computer discs, and seals bleeding ulcers. The intensity and specific wave– length of the light determines how it will interact with what it touches. Graduate student Fahad Al-Mashaabi is conducting new research with C02 lasers. The wavelength created by the lab's argon gas laser appears brilliant green to the human eye. PSU doctoral can– didate Duncan Macfarlane is manipu– lating and monitoring this beam in his experiments. Careful not to wear a watch or any jewelry, Macfarlane must be sure the ray does not accidently reflect into his eyes. Light of this par– ticular color will bypass the relatively transparent outer tissues of the eye to coagulate blood in the retina, a plus during delicate eye surgery, but hazardous in the lab. Within this laser the argon ampli– fied light bounces between mirrors like a ping pong ball. The flow of light appears continuous but it is actually constantly interrupted by a tiny, $20,000 shutter placed at one end of the laser. By blinking the light, small packets of energy are produced. "These packets or short pulses of light are repeated 80 million times per second," says Macfarlane, "which is so fast that we see the light as a steady beam." Macfarlane's experiment is to let a little of this light leak off one end of the laser and, using mirrors, direct it into different measuring devices and into a second dye laser. The dye laser converts the light into even shorter PSU MAGAZINE PAGE5 pulses, about a trillion times briefer than a photographer's flash , according to Casperson. These ultrashort pulses, a picosec– ond in duration, put this experiment in the forefront of laser research. And it is this kind of work that attracts stu– dents like Macfarlane to Casperson's lab. "The name of the game in laser technology is to control and package light energy in new ways," explains Casperson. By regulating the pulses created by the argon-dye laser combi– nation, Casperson and Macfarlane hope to make it a useful tool for scientists studying molecules, specific genes, and ultrafast biological reac– tions such as vision. Local high tech firms, most notably Tektronix, are already using the dye laser. The Beaverton company, which donates firstline equipment for the lab's use, occasionally sends research teams by to calibrate equipment and test materials using the laser's unique capabilities. "They tell us we have the best pulses in town," Casperson says with a grin. Recently Casperson and his stu– dents found that commercially manu– factured lasers designed to emit ultra– short pulses sometimes produce erratic light bursts, an obvious problem to