Physicists probe mystery of black silicon
A 200-milliJoule pulse laser fires in this timed exposure Oct. 9, 2009, at the U.S. Air Force Academy in Colorado Springs, Colo. The laser is used for a variety of experiments, including tests to determine how "pushing" sulfur into a silicon-based solar cell increases the cell's efficiency. (U.S. Air Force photo/Rachel Boettcher)