The Cherenkov Telescope Array (CTA) project aims to implement the world’s largest next generation of Very High Energy gamma-ray Imaging Atmospheric Cherenkov Telescopes devoted to the observation from a few tens of GeV to more than 100 TeV. To view the whole sky, two CTA sites are foreseen, one for each hemisphere. The sensitivity at the lowest energy range will be dominated by four Large Size Telescopes, LSTs, located at the center of each array and designed to achieve observations of high red-shift objects with the threshold energy of 20 GeV. The LST is optimized also for transient low energy sources, such as Gamma Ray Bursts (GRB), which require fast repositioning of the telescope. The overall design and the development status of the first LST telescope will be discussed.
This paper describes a micro-angle sensor based on laser autocollimation. The sensor consists of a light source, an objective lens and a positioning-sensing device. The position-sensing photodetector, which is a quadrant photodiode, is placed at the focal position of the objective lens. Differing from a conventional autocollimator, the angle sensor employs a laser diode as the light source. The laser beam is collimated to a thin parallel beam with a diameter of 1 mm so that the angle sensor can be used to detect the surface local slope of a specimen. The thin laser beam also makes it possible to use a small target mirror for measurement of stage angular error motions. Because the sensitivity of angle detection does not depend on the focal length of the objective lens by using a laser source, an objective lens with a short focal length is employed for realizing a compact sensor size. The prototype micro-angle sensor has a dimension of 26mm x 22mm x 12 mm. The resolution is better than 0.1 arc-seconds. Optical design and experimental results of confirming the performance of the sensor are presented.