The Laser calibration system for LHAASO-WFCTA

The Wide Field-of-view Cherenkov Telescope Array (WFCTA) of Large High Altitude Air Shower Observatory (LHAASO) is designed to measure the Cherenkov and fluorescent light created in the extensive air showers by cosmic rays (CRs) from ∼30 TeV to several EeV. In order to achieve an end-to-end calibration method for WFCTA, three Laser lidar facilities have been installed at LHAASO. They feature two N₂ and one YAG Lasers which direct calibrated and pulsed beams into sky. Light scattered from Laser beams produces tracks recorded by the telescope detectors. The Laser calibration systems are used to investigate properties of the atmosphere and air fluorescence. In this paper, we introduce the design and performance of the Laser facilities at an altitude of 4410 m. Great cares were taken to select the data collected by telescopes at clear nights for our analysis. After excluding the inconsistency of all SiPMs of the telescope, we find that the experimental data of the images collected by telescopes agree noticeably well with Monte Carlo’s simulation.