The French National Metrology Laboratory, the LNE-LCM, uses a cryogenic radiometer as the basis for its optical radiation measurement scales. This instrument is an absolute radiometer operating at 4.2 K based on the electrical substitution method. It allows absolute measurements of the optical power of laser beams with a relative standard uncertainty in the range of 5 parts in 105. A new cryogenic radiometer was installed in the laboratory and the present paper describes its complete metrological characterization which allows to achieve this level of uncertainty.

Key words

optical radiation
cryogenic radiometer
primary reference
spectral responsivity