Methods that prevent oxygen inhibition of a light-initiated polymerization reaction by purging the oxygen from reaction surfaces using inert gas flow. In some embodiments, oxygen is purged using a gas diffusion system that introduces, via a diffuser, an inert gas into a workspace between a UV light source and a UV curable layer of a workpiece. The diffuser may be made of a transparent or diffuse material to allow UV light to pass through it, and includes an array of micro-holes for the gas to pass through towards the workpiece. The inert gas flow may be heated to maintain a desired and uniform reaction temperature.