WFC3 TV3 Testing: IR Channel Throughput

A new IR detector (IR4; FPA165) was housed in WFC3 in the recent campaign of thermal vaccum (TV) testing at GSFC. We performed measurements of the IR channel throughput and found that it exceeds by ~2-8% expectations from component measurements over the entire wavelength range of the channel. This is in contrast to the results of the first WFC3 TV test in 2004 and the second WFC3 TV test in 2007. In 2004, the first IR detector (IR2; FPA064) was in the instrument, and we found a grey deficiency of 15% in the measured throughput. In 2007, the second IR detector (IR1; FPA129) was in the instrument, and we found a deficiency that smoothly varied from about 2% on the blue end of its range to 20% on the red end of its range. At the component level, IR4 was already expected to be far superior to the previous two detectors (in QE and other parameters), so this finding amplifies that superiority. The throughput measurements in the current campaign were repeated several times with outstanding consistency (~1%).