Laser test with Mini-EUSO

TL;DR

Mini-EUSO is a space-based UV detector on the ISS designed to observe cosmic-ray air showers, and a steerable UV laser system is tested to calibrate and evaluate its performance.

Contribution

This paper reports on the testing of a mobile UV laser system to calibrate and validate Mini-EUSO's cosmic-ray detection capabilities from space.

Findings

Laser system stability within 5%

Laser pulses simulate EAS brightness for energies up to 10^21 eV

Implementation of laser characteristics in simulation framework

Abstract

Mini-EUSO (Extreme Universe Space Observatory) is a small-scale prototype cosmic-ray detector that will measure Earth`s UV emission and other atmospheric phenomena from space. It will be placed in the International Space Station (ISS) behind a UV-transparent window looking to the nadir. The launch is planned this year (2019). Consisting of a multi-anode photomultiplier (MAPMT) camera and a $25$ cm diameter Fresnel lens system, Mini-EUSO has a \ang{44} field of view (FoV), a $6.5$ km$^2$ spatial resolution on the ground and a $2.5\ \mu$s temporal resolution. In principle, Mini-EUSO will be sensitive to extensive air shower (EAS) from cosmic-rays with energies above $10^{21}$ eV. A mobile, steerable UV laser system will be used to test the expected energy threshold and performance of Mini-EUSO. The laser system will be driven to remote locations in the Western US and aimed across the field of view of Mini-EUSO when the ISS passes overhead during dark nights. It will emit pulsed $355$ nm UV laser light to produce a short speed-of-light track in the detector. The brightness of this track will be similar to the track from an EAS resulting from a cosmic-ray of up to $10^{21}$ eV. The laser energy is selectable with a maximum of around $90$ mJ per pulse. The energy calibration factor is stable within $5\ \% $. The characteristics of the laser system and Mini-EUSO have been implemented inside the JEM-EUSO OffLine software framework, and laser simulation studies are ongoing to determine the best way to perform a field measurement.