TA-DPG-2018-018

The PANDA experiment at FAIR (Facility for Antiproton and Ion Re-
search in Europe) at GSI, Darmstadt, will study fundamental questions
of hadron physics and QCD. A compact, fast focusing Ring Imaging
Cherenkov counter using the DIRC (Detection of Internally Reflected
Cherenkov light) technology, will provide charged particle identifica-
tion (PID) in the barrel region of the PANDA experiment. To meet
the PANDA PID requirements, the Barrel DIRC has to provide pre-
cise measurements of the Cherenkov angle, which is conserved for
Cherenkov photons propagating through the radiator by total internal
reflection. The radiators, rectangular bars made from synthetic fused
silica, have to fulfill strict optical and mechanical requirements. This
includes squareness and parallelism of the bar sides, sharp corners,
and smoothly polished surfaces in the order of 10 Å, ensuring very lit-
tle angular distortions and high transport efficiency. An optical setup,
consisting of a computer-controlled positioning and multi-wavelength
laser system, is used to evaluate the bars to obtain critical values like
transmittance and reflectivity. Prototypes from various manufacturers
using different production techniques have been tested to qualify ven-
dors for the Barrel DIRC bar production. Setup, measuring procedure
and measurement results will be presented in this contribution.