Bokeh Mirror Alignment for Cherenkov Telescopes
Abstract
Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with large apertures and high image intensities to map the faint Cherenkov light emitted from cosmic ray air showers onto their image sensors. Segmented reflectors fulfill these needs, and composed from mass production mirror facets they are inexpensive and lightweight. However, as the overall image is a superposition of the individual facet images, alignment remains a challenge. Here we present a simple, yet extendable method, to align a segmented reflector using its Bokeh. Bokeh alignment does not need a star or good weather nights but can be done even during daytime. Bokeh alignment optimizes the facet orientations by comparing the segmented reflectors Bokeh to a predefined template. The optimal Bokeh template is highly constricted by the reflector's aperture and is easy accessible. The Bokeh is observed using the out of focus image of a near by point like light source in a distance of about 10 focal lengths. We introduce Bokeh alignment on segmented reflectors and demonstrate it on the First Geiger-mode Avalanche Cherenkov Telescope (FACT) on La Palma, Spain.
Cite
@article{arxiv.1605.06277,
title = {Bokeh Mirror Alignment for Cherenkov Telescopes},
author = {M. L. Ahnen and D. Baack and M. Balbo and M. Bergmann and A. Biland and M. Blank and T. Bretz and K. A. Bruegge and J. Buss and M. Domke and D. Dorner and S. Einecke and C. Hempfling and D. Hildebrand and G. Hughes and W. Lustermann and K. Mannheim and S. A. Mueller and D. Neise and A. Neronov and M. Noethe and A. -K. Overkemping and A. Paravac and F. Pauss and W. Rhode and A. Shukla and F. Temme and J. Thaele and S. Toscano and P. Vogler and R. Walter and A. Wilbert},
journal= {arXiv preprint arXiv:1605.06277},
year = {2016}
}
Comments
accepted for publication in Astroparticle Physics