Development of a UV laser test bench for micro-pattern gaseous detectors

This work describes the development of a laser test bench for micro-pattern gaseous detectors. The setup is made of a pulsed UV laser of 50 μJ single-pulse energy; the laser beam enters a gaseous detector placed at one end of the bench, it frees electrons by two-photon (or multi-photon) ionization of impurities in the gas. The radius, intensity and Rayleigh range of the laser beam can be adjusted with an attenuator and a set of pinholes and lenses to obtain a collimated or a focused beam, in order to control the ionization position and density inside the gas. The setup is validated on a Time Projection GEM (TPG) prototype with a large drift gap (40 mm) to observe the presence of two-photon ionization processes and determine the ionization density as a function of the beam intensity and radius; its future scope of application involves the calibration of a prototype of Fast Timing MPGD (FTM), whose geometry is not suited for testing with more common calibration techniques like those involving X-ray sources.