The relationship of beam quality and weld depth of penetration was studied to attempt to better quantify the operation of CO{sub 2} laser beam welders. Equipment to measure laser beam quality was obtained. The equipment was calibrated using standard apertures. To relate weld penetration and beam quality measurements, it was necessary to force changes in the CO{sub 2} laser welder`s operation. The chosen experimental variables were laser gas mixture and the use of a group of focusing lenses that had been used in production.