Measuring the spatial intensity distribution of high-power focused laser beams using a rotating-wire type laser beam analyser. II. Experimental validation

Abstract

The theory and application of a rotating-wire type laser beam analyser (LBA) device for measurement of both the spatial distribution of power density and beam 'diameter' of a converging/diverging (focused) high-power laser beam are presented. In part 1 of this article, geometrical optics were used to analyse the theory of operation of the LBA. These analyses showed that operation and correct interpretation of measured results from the LBA are strongly dependent upon the relative position of the LBA measurement plane and the laser beam focal plane. In this article the results of LBA measurements of the laser power density distribution from a 250 W mean power, pulsed Nd:YAG laser welder are presented and compared with the derived theory of operation of the LBA. The sample area path of the LBA through the laser beam was determined experimentally and was found to agree with the theoretically predicted path. Also, the theoretically predicted effects of sample area dimensions relative to the measured beam diameter on distortion of the measured power density distribution were confirmed experimentally. Finally, LBA measurements made near the focal point of beams from the high-power pulsed Nd:YAG laser were shown to agree with measured beam 'diameter' and power density distributions obtained using the Kapton film burn pattern technique. It is shown that with careful operation and interpretation of measured results, the LBA can be used to measure accurately the spatial distribution of power density and the beam 'diameter' of unattenuated, focused laser beams from high-power lasers.