A noninvasive technique was developed to measure the temperature distribution in laser gain medium. Both axial and radial temperature distributions of a diode-laser-pumped and intracavity frequency-doubled high-power Nd:YVO4/KTP laser were characterized using a high dynamic range, low-coherence reflectometer. This measurement is important to the design of high-power solid-state lasers both in terms of mode matching and laser-rod doping selection. (C) 1998 American Institute of Physics. [S0003-6951(98)03649-3].