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Investigation of UV laser ionisation in argon-based gas mixtures with a Triple-GEM detector

In the gas detectors, the ionisation mechanisms of the charged particles and X-ray/γ-photons are well studied by theory and experiment. However, on the experimental measurements of the ionisation ability of the lasers, publications only give the estimation results. This study aims to fill the gap and measures the laser ionisation precisely. A GEM detector and an optical system have been set up to measure the laser ionisation. The purity of each component of the gas mixtures is indicated in this study. Our research shows that a pulsed laser with a wavelength of 266 nm can generate 100–200 electrons per centimeter, which equals to the ionisation produced by 1–2 Minimum Ionising Particles (MIPs) in argon-based mixtures. Furthermore, this study gives an experimental reference to select the laser energy density in argon-based gas mixtures when applying lasers to calibration in the gaseous detectors. We have also studied the impacts of different vendors and gas flow rates on the ionisation created by UV laser pulses.