June 9, 2016

AREAL Femtosecond Laser System Upgrade

In May 26-31, 2016, the “Photon Beams & Optics” group has performed a maintenance and upgrade of the AREAL ultrashort laser system, including the installation, alignment and adjustment of a new laser beam profiling unit.

The laser beam profiling system consists of a camera (Spiricon SP620U, OPHIR Optronics Solutions Inc.) with beam attenuation and beam sizing optics which forms a switchable optical path for measurement and monitoring of the spatial distribution of the ultrashort UV pulses driving the AREAL linac. Dedicated software is used for spot-size measurements and profile analyses.

Besides the regular use for laser servicing and beam quality monitoring, the new setup will serve as a supplementary quantitative (diagnostic) tool for prospective experiments which are sensitive to photoemission flux and electron beam charge. In particular, the photon flux (and, hence, the photoemission intensity) in the vicinity of the photocathode can now be varied in a quantitatively controlled way, so that the laser spot size and intensity spatial distribution are measured/derived while varying the illuminated area of cathode (by means of a distant iris).

The UV laser beam profile, measured by the new setup, was taken as a quality criterion during the recent maintenance and servicing of the laser system. A better quality (nearly a Gaussian) spatial distribution of the beam was obtained by correcting the slight misalignment in the FHG module.