Production via thermal slumping of large glass monolithic secondary mirrors (1.8 m diameter) for Schwarzschild-Couder air-Cherenkov gamma-ray telescopes

Abstract

The standard design for 4-meter diameter class Imaging Atmospheric Cherenkov Telescopes (IACTs) used in groundbased gamma-ray astronomy is the dual-mirror Schwarzschild-Couder-like configuration. This design has been adopted for the telescopes in the ASTRI-Horn and ASTRI Mini-Array experiments (1 + 9 telescopes) and the construction of the 37 telescopes in the Small Size Telescope (SST) sub-array of the Cherenkov Telescope Array Observatory (CTAO) in Chile. The design provides an aplanatic optical response across a field of view wider than 10 degrees and is suitable for compact cameras using small pixels such as SiPM sensors. The telescopes feature secondary mirrors with a diameter of 1.8 meters, made of monolithic glass using a hot-slumping replication process. The paper discusses the manufacturing and characterization results of the prototype mirrors.