Plexiglas (polymethyl methacrylate PMMA) burn-ins have been the standard for raw beam analysis of CO2-lasers for a long time. Different beam diameter definitions have been established based on the mechanical dimensions of these Plexiglas burn-ins, usually derived from the diameter at a certain threshold (e. g. full width at 50% or 30% maximum height). These definitions are widely used, especially for service applications, but also in science and engineering.
The more recent definitions of a beam diameter, as given for example in the DIN EN ISO 11146, are based on the second order moments. These are accessible only via computer based calculations, and require the power density distribution as a 2-dimensional electronic data matrix.
Generally, it is assumed that beam diameters derived from such different algorithms cannot be compared.
We will show the theoretical basis that allows the generation and recalculation of beam diameters that have been derived from Plexiglas burn-ins on the one side and electronic measurement equipment on the other side. The prerequisites under which such recalculations are possible are discussed.
Traditional Plexiglas burn-ins are also used for a qualitative evaluation of stray light (Randfelder) and symmetry. Standard beam diagnostic devices do not have the resolution and dynamics to make a completely satisfying transition from Plexiglas to electronic measurements. We will provide information on the amount of dynamics that is required to achieve a similar resolution for low intensity features of a laser beam.
Similar results and a similar presentation can facilitate the transition from semi-quantitative Plexiglas burn-ins to beam analysis with electronic equipment, that does not produce carcinogenic fumes like Plexiglas burn-ins can do.