Thursday, August 23, 2012

On ODI's throughput

ODI at WIYN's sensitivity has been predicted based on modeling all optically relevant components. The throughput model includes: The atmospheric extinction and telluric absorption lines, the three telescope mirrors, absorption losses in the ODI optics (two lenses and two ADC prisms), anti-reflection coating performance, and the quantum efficiency of the OTA detectors. The predicted throughput has been verified on sky in the g', r', i', and z' bands within reasonable error margins, and the differences we found are now included in the throughput model as a fudge factor. The resulting as-build throughput of ODI is shown the figure below. We will keep tweaking this model as we get more on-sky data; I am in particular looking forward using a u'-band filter at some point in the future and verify the blue performance

The blue cut-off in ODI's sensitivity  is governed by special glass (O'Hara PBL6Y) in the ADC prisms. The fall-off in the red is driven by the vanishing quantum efficiency of the ODI detectors. The peak throughput of order of 55\% is the sum of all losses in the system; the most significant limit on the peak throughput is set by the losses in the three WIYN mirrors, though. 

Total system throughput of the WIYN telescope and ODI, including atmospheric absorption.

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