Wire calorimeter for absolute and accurate laser-power measurements

A calorimeter, acting in a self-balancing bridge circuit and designed for absolute measurements of radiation power from continuous-wave lasers, is described. The calorimeter contains a wire-cone absorber with an effective absorptivity of 99.5±0.2%. The arrangement, consisting of a d.c. bridge, a galvanometer amplifier and a transistor current regulator, is suitable for absolute-power measurements in the range 30¿W to 30mW with an accuracy of within 1%.