A POLYMER THAT CAN TRANSFER ENERGY BETWEEN DIFFERENT LIGHT BEAMS has been demonstrated by researchers at UC-San Diego (W.E. Moerner, 619- 822-0453), opening possibilities for inexpensive and easily manufacturable "optical transistors" that can amplify or attenuate a light beam. The San Diego polymer is an example of a "photorefractive" material, a material that adjusts its structure and electronic properties when two or more light beams combine on it to form an interference pattern. On these materials, light from one beam can bend in such a way as to bounce back in the direction of a second beam, adding energy to it. Inorganic versions of these materials exist, but they are difficult to make and can cost thousands of dollars for a tiny cube. Moerner constructed a polymer whose three main components carried out essential tasks: buckyballs offer electrons, poly (n-vinyl carbazole) (PVK) molecules carry these electrons along their backbone, and PDCST molecules stretch or contract, changing the way light bends in these regions. The researchers demonstrated a "net gain" of about 5, in which one of the laser beams shining on the material gained energy. These materials have numerous possible applications, including correcting distorted images. (Science, 25 July.)