ИСТИНА

A new imaging photometer was developed and installed at Verkhnetulomsky observatory (68°36’N,31°47’E) to measure the fine structure of auroral emission in near-UV range with high temporal resolution.The photometer has a wide field-of-view (20° FOV), a high temporal resolution (2.5 μs – 40 ms in differentmodes), an angular resolution of about 1.2° and an aperture 5 cm. The photodetector placed in a focal planeof the lens consists of 4 multi-anode photomultiplier tubes (MAPMTs) with 256 channels in total operatingin a single photoelectron counting mode. This provides a high sensitivity of the device. Before installation of the detector to the observatory measurements of the photo detector structure and itscalibrations were carried out using the method previously developed in the JEM-EUSO collaboration forultra-high-energy cosmic rays detector photo detection modules. The calibration of the 4 MAPMTs wasperformed in a special set-up consiting of the non-transparent blackbox, light source (an LED with awavelength of 405 nm), integrating sphere which provides uniform illumination and a power meter with 2NIST photodiodes for precise light power measurements. One photodiode is located inside the integratingsphere to control the intensity of emission. At the first step of calibration, the second photodiode is placed instead of MAPMTs, the light power of LEDis high and it allows us to measure the power on both photodiodes and calculate a cross-calibrationcoefficient. At the next stage the photodetector module is placed instead of photodiode and the light powerof the LED is decreased to obtain single photon flux on the pixel surface per gate time unit (GTU). Knowingthe cross-coefficient, areas of photodiode and pixels, measurements of the photodiode inside the sphere, andnumber of photoelectrons on each pixel, it is possible to calculate the number of photons and efficiency foreach pixel. According to this measurements the individual parameters of each channel can be obtained andoptimized (individual thresholds of discriminator). Results of calibrations using both methods and its application to measurements are presented in the talk. Theresearch is supported by a grant from the Russian Science Foundation (project No.22-62-00010)