Heat transfer analysis and modeling of a cryogenic laser radiometer

This study investigates the laser optimized cryogenic radiometer (LOCR) recently acquired by the National Institute of Standards and Technology in Boulder, Colorado, to calibrate laser power meters and detectors. The objectives are to evaluate potentially significant sources of uncertainty in the radiometric measurements and to develop transient models that efficiently and accurately predict the behavior of this radiometer. The analysis suggests that radiation from the Brewster window assembly may cause the total power entering the radiometer to drift more than 130 nW for a room temperature variation of 0.2 K, Steady-state modeling of the LOCR with finite element analysis software indicates a relative inequivalence between optical and electrical heating of 4 x 10(-6) at the 1-mW power level. A new thermal model has been developed to simplify transient predictions by combining lumped parameter and one-dimensional elements. This model outperforms single-time-constant exponential models and can be expanded to simulate the complete radiometer system.