While LOCR uses ac bridge electronics located directly under the cryostat, HACR uses a dc measurement of the temperature.
HACR and LOCR measured the two trap detectors, labeled TSO2 and NIST 6 using the optical setups, protocols, and uncertainties described in their respective papers [1, 2].
With the LOCR, the absorbing cavity and the cavity heat sink are maintained at constant temperatures by electrical control systems.
The LOCR's optical power measurement is transferred by physically substituting the trap detectors into the beam path, the same plane in which the LOCR's cavity was located.
While the methods of measuring optical power are similar for both LOCR and HACR, there is a critical difference in the procedures used to align the trap detectors.
Also, the potential difference in the laser's incident angle in the HACR and LOCR calibrations resulted in a slightly different measured spatial uniformity for the traps.
These uncertainties do not reflect any effects of trap detector spatial nonuniformities or incident angle, but only the uncertainties in calibrating a trap detector from HACR or LOCR (Tables 2 and 3).
The traps were aligned as in the LOCR measurements, with the incoming beam at near normal incidence to the entrance aperture, and the center of the beam aligned to the nominal center of the aperture.
