Application of the nitrogen laser calibration system in LHAASO-WFCTA

Abstract

The nitrogen laser calibration system for the Wide Field of View Cherenkov Telescope Array (WFCTA) is one of the most important components of the Large High Altitude Air Shower Observatory (LHAASO). This calibration system is composed of three parts, including a high-precision 3D lifting and rotating platform (HiRoP), a nitrogen laser and the wide field of view Cherenkov telescope prototypes. The accuracy of the HiRoP is of great importance for the precise calibration of WFCTA since it controls the laser beam’s pointing direction. A home-made HiRoP was introduced and the measurements implies that the angular and lifting accuracies of HiRoP are better than 0.003° and 0.075 mm, respectively. Furthermore, the pulse energy stability of the nitrogen laser beam is another remarkably important factor. The nitrogen laser system with a wavelength of 337.1 nm located in a high-precision temperature and humidity’s controlling container, resulting in a pulse energy fluctuation less than 3 percent. Besides, the method of a standard zero point verification is employed to improve the long-term accuracy of the beam pointing direction.