AbstractThe absorption spectra for single crystal and polyerystalline UO2have been measured between 0.6 and 15μm at room temperature. The spectrum for UO2resembles that of a typical semiconductor, opaque in the visible but transparent over a large portion of the infrared. An absorption edge is located at approximately 0.6μm (2.0 eV). A large optical window extends from 3 to 13μm.The absorption coefficient for single crystal UO2has been determined between 1.5 and 15μm. A maximum value of 57 cm-1was measured at 1.70μm with minimum values of 6 cm-1at 2.75 and 8μm. The absorption coefficient of polyerystalline UO2at wavelengths less than 8μm is estimated to be ten times larger than for single crystal UO2.