Abstract
The KDP rod in an electrooptic light modulator is heated uniformly in its cross section by the rf field but is cooled only at the surface. Therefore, a radial thermal gradient exists in the rod. We show experimentally and analytically that this gradient degrades the performance of the device when operated as an intensity modulator. For example, about 2 W dissipated in a cylindrical KDP rod of any dimensions will reduce the degree of intensity modulation by one half. The sources and effects of random-phase retardation are also considered briefly.