Localisation: characterisation of laser beam shape for materials processing using a new parameter

Abstract

This work is motivated by the observation that the shape of a laser power density distribution (PDD) significantly influences the manufacturing quality in numerous laser processes. Lacking appropriate PDD shape parameters this influence, however, is not described quantitatively by few characteristic figures of the PDD. The paper presents a new quantitative, application adapted few parameter characterisation of PDD shape. For nearly circular PDDs the localisation as just one additional parameter on top of the common characteristics beam power and PDD radius is introduced and proven as meaningful. The localisation is based on the fourth moment of the PDD. This ensures simple optical transformation properties and thus easy adjustability of the localisation of the laser beam as manufacturing tool. Together with beam power and radius the localisation allows to determine the power fractions in the central and ring-like outer region of the PDD as well as the fraction outside the PDD radius. This will be shown by application of evaluation functions which evaluate the spatial regions of the PDD with different weights. Applications to real beams used for laser manufacturing will be demonstrated. For the examples of surface dominated laser processes it will be shown briefly that this approximate shape description with one additional parameter allows an estimate of PDD influence on manufacturing quality. An outlook on further shape characterising parameters is given.