  A key enabling technology for many liquid noble gas (LNG) detectors is the
use of the common wavelength shifting medium tetraphenyl butadiene (TPB). TPB
thin films are used to shift ultraviolet scintillation light into the visible
spectrum for detection and event reconstruction. Understanding the wavelength
shifting efficiency and optical properties of these films are critical aspects
in detector performance and modeling and hence in the ultimate physics
sensitivity of such experiments. This article presents the first measurements
of the room-temperature microphysical quantum efficiency for vacuum-deposited
TPB thin films - a result that is independent of the optics of the TPB or
substrate. Also presented are measurements of the absorption length in the
vacuum ultraviolet regime, the secondary re-emission efficiency, and more
precise results for the "black-box" efficiency across a broader spectrum of
wavelengths than previous results. The low-wavelength sensitivity, in
particular, would allow construction of LNG scintillator detectors with lighter
elements (Ne, He) to target light mass WIMPs.
