Abstract: A boresight thermal reference source capable of rapidly providing a uniform high intensity Infra-Red signal, comprises a boresight source housing, a ceramic rod, and a heater wire helically surrounding, at least partially, the ceramic rod. The coiled heater wire has a plurality of turns extending outwardly from one end of the ceramic rod forming a blackbody cavity therein from the plurality of outwardly extending turns on the end of the ceramic rod. The small mass of the ceramic rod, optimum geometry of ceramic rod, heater wire, and housing for reduced heat loss, and the aforementioned blackbody cavity configuration, all provide for low operating power with uniform rapid heating of one end (ceramic floor) of the ceramic rod to about 1000.degree. C.