Conference Paper

Development of cold-slumping glass mirrors for imaging Cherenkov telescopes

DOI: 10.1117/12.790631 Conference: Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series


The development of lightweight glass mirrors manufactured via cold-slumping technique for Imaging Atmospheric Cherenkov Telescope is presented. The mirror elements have a sandwich-like structure where the reflecting and backing facets are composed by glass sheets with an interposed honeycomb aluminum core. The reflecting coating is deposited in high vacuum by means of physical vapor deposition and consists of aluminum with an additional protective layer of SiO2. The mirror fabrication and environmental qualification by accelerated ageing, thermal cycling and coating adhesion are presented together with the optical performances measured as angular resolution and reflectivity obtained on spherical, 1 squared meter mirror prototypes.

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Available from: Enrico Giro, Jan 03, 2014
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    • "The cold glass slumping technology, developed by Media Lario Technology (MLT), Italy, has been adapted for the production of the aspheric primary mirror panels [5]. During this process, two 1.7 mm sheets of glass are assembled on each side of a 30 mm aluminum honeycomb core and slumped to required figure on a precisely machined mandrel. "
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    ABSTRACT: We present the design and the status of procurement of the optical system of the prototype Schwarzschild-Couder telescope (pSCT), for which construction is scheduled to begin in fall at the Fred Lawrence Whipple Observatory in southern Arizona, USA. The Schwarzschild-Couder telescope is a candidate for the medium-sized telescopes of the Cherenkov Telescope Array, which utilizes imaging atmospheric Cherenkov techniques to observe gamma rays in the energy range of 60Gev-60TeV. The pSCT novel aplanatic optical system is made of two segmented aspheric mirrors. The primary mirror has 48 mirror panels with an aperture of 9.6 m, while the secondary, made of 24 panels, has an diameter of 5.4 m. The resulting point spread function (PSF) is required to be better than 4 arcmin within a field of view of 6.4 degrees (80% of the field of view), which corresponds to a physical size of 6.4 mm on the focal plane. This goal represents a challenge for the inexpensive fabrication of aspheric mirror panels and for the precise alignment of the optical system as well as for the rigidity of the optical support structure. In this submission we introduce the design of the Schwarzschild-Couder optical system and describe the solutions adopted for the manufacturing of the mirror panels and their integration with the optical support structure.
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    • "The radius of curvature of the hexagonal mirror segments required for the SST-DC is approximately 23 m and their size is 1.05 m flat-to-flat. These are being developed by IFJ PAN using glass cold slumping technology, developed at the INAF-Brera Astronomical Observatory [4][5], and an open structure composite mirror design. FEA studies have demonstrated that it may be difficult to achieve the required radius of curvature using the cold slumping technique: the stresses induced in the glass sheet as it is moulded are potentially too high and cause the mirror to have a short lifetime. "
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    Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 09/2012
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