TN-DIR-2018-001

Abstract
The main component of the PANDA Barrel DIRC detector are 2:4m long synthetic fused silica
("quartz") bars with a rectangular cross section which are used as radiators and light guides. The
Cherenkov photons produced by a charged particle traversing the bar are reflected internally many
times before they reach the readout end of the bar. To guarantee a sufficiently high resolution of
the detector, these bars have to meet tight optical and mechanical specifications. Autocollimator
measurements on prototype bars of different manufacturers have been performed to very precisely
determine the squareness and parallelism of the bars. This method has been employed to see which
of the bars can meet the specifications and would be adequate to be used for the detector. So
far, bars by Lytkarino, Zeiss, Heraeus, InSync and Zygo have been measured. Furthermore the
measuring method ought to be applied in the future for quality assurance of the detector bars.
The measuring method and the results are described in this note.