Number 423 (Story #4), April 14, 1999 by Phillip F. Schewe and Ben Stein|
POWDER LASER. Physicists at Northwestern have for the first time observed laser action in zinc oxide and gallium nitride powders (Cao et al., Physical Review Letters, 15 March). Semiconductor powders would normally absorb or even "halt" light (see Update 356), but because in the Northwestern samples the average length between scattering from the tiny (100 nm) grains is less than the light's wavelength, the light can propagate and even augment itself by stimulating further emission from atoms in the powder (Science, 2 April). This is laser action and the powder constitutes a sort of "random laser," one in which light moves not between the fixed mirrors of a cavity but, in random directions, among trillions of grains.