AN AMBIENT BACKGROUND TRANSFER STANDARD RADIOMETER

The need exists for a very stable, portable radiometer which can trans fer readings from an absolute measuring cryogenic radiometer operating in a vacuum chamber to other laboratories. This will allow electro-op tical instruments operating in either air or vacuum to be calibrated r elative to the single absolute measuring cryogenic standard. It will a lso allow characterization of vacuum chamber windows by comparing meas urements made in front of and behind the windows. To perform these fun ctions the transfer standard must have good radiometric sensitivity an d long-term repeatability in both air and vacuum. It must be reasonabl y compact and portable and must operate over a wide range of ambient t emperatures. Ideally, the transfer standard is linear over a large dyn amic range with direct readout in watts or watts/cm2 or watts/cm2.sr a nd has a flat spectral response from UV to far-infrared wavelengths. S uch a transfer standard radiometer utilizing a dual-cavity detector is described. The dynamic range, radiometric accuracy and long-term stab ility of the transfer standard radiometer is presented. Stability data of better than 0,001 % per day in air is shown.