WFC3 TV3 Testing: System Throughput on the UVIS Build 1’ Detector

The UVIS flight detector (UVIS build 1’) was installed in WFC3 prior to its third and final campaign of thermal vacuum ground testing. We performed testing of the end-to-end system throughput on the UVIS channel, and found that it performs near or better than expectations at most wavelengths. However, the measured throughput is significantly different than that measured for this detector in the first campaign of thermal vacuum testing. This is due to two systematic changes that generally work in opposite directions. First, the sensitivity of the ground reference detector was revised downward in the UV, which produces a corresponding change in sensitivity for the WFC3 detector. Second, the quantum yield correction (accounting for the fact that there is a finite chance of producing two electrons from a single incoming UV photon) was found to be very small for this detector, meaning that the true UV sensitivity of this detector is nearly as high as the raw sensitivity.