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O: Fachverband Oberflächenphysik
O 79: Experimental methods
O 79.6: Talk
Thursday, March 29, 2012, 17:15–17:30, A 060
Optimizing the sensitivity of energy-selective photon detectors for use in inverse photoemission: VUV-transmission properties of CaF2 windows — •Christian Thiede, Karen Zumbrägel, Matthias Rüter, Anke B. Schmidt, and Markus Donath — Westfälische Wilhelms-Universität, Münster, Nordrhein-Westfalen
Band-pass photon detectors are widely used in inverse-photoemission experiments performed in the isochromat mode. In Geiger-Müller counters, the band-pass behavior is realized by combining the photoionization threshold of a suitable counting gas (high pass) with the transmission characteristics of an alkaline earth fluoride window (low pass). Since inverse photoemission generally suffers from a low photon yield, an optimized detector efficiency is crucial for this technique.
One of the critical parameters is the transmission characteristics of the entrance window. We present transmission measurements for CaF2 windows in the vacuum-ultraviolet spectral range in the vicinity of the transmission cutoff as a function of crystal purity as well as surface finish, adsorbate coverage, thickness, and temperature. Our findings reveal that the sensitivity of the photon counter depends critically on these window parameters.