High-fidelity analysis of the electro-optical non-equivalence of planar electrical substitution radiometers^*

Abstract We present the results of a finite element analysis of the electro-optical non-equivalence of planar electrical substitution radiometers with vertically aligned carbon nanotube absorbers, operating at either room or cryogenic temperature. These detectors are the basis of the new room temperature standards of the Laboratory for Atmospheric and Space Physics’ (LASP) Total solar irradiance Radiometer Facility and the Spectral solar irradiance Radiometer Facility, and the NIST Boulder open beam cryogenic radiometer facility. We show that the detector of our cryogenic electrical substitution radiometer has no significant electro-optical non-equivalence. Further, we also show that with careful detector design, the non-equivalence can be minimized at room temperature. It was found that in general the non-equivalence cannot be deduced from the temperature mismatch between the electrical and the optical states without considering the conductance mismatch and optical power input. The results are regarded as being precise rather than absolute to account for potentially unknown modeling errors. The numerical accuracy is typically less than 5 ppm.