A similar process could lead to a compact source of coherent x rays.
Lasers come in infrared and visible varieties, but none yet in the x-ray band.
A compact and powerful source of coherent x rays is the dream of many physicists, who see applications such as making atomic scale, three-dimensional movies of a melting crystal or an operating photosynthesis protein. In a step toward that goal, a research team has detected high frequency coherent light generated by a new process. As they report in the 12 June PRL , intense laser pulses can stimulate free electrons in a plasma to emit coherent light at triple the input frequency in a narrowly-directed cone. The authors say that much higher frequencies should be possible in the future, but their other goal is to learn more about the poorly understood interactions between light and electrons under these extreme conditions. Zap an electron with a normal laser pulse, and the light will scatter essentially unchanged.