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

Abstract

The beam 'diameter' or 'spot size' and the spatial distribution of power density at the focal point of the high-power laser beams used in laser materials processing applications are fundamental process parameters. The ability to measure these process parameters accurately is essential for effective control of these laser materials processes. In this two part article, 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 this article, theoretical analyses using geometrical optics are presented for the determination of the sampling path through the beam, the spatial resolution of the LBA, and the transformation relationship between the output voltage versus time signal produced by the LBA detector and the desired power density versus spatial position data. The 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. This work shows that the LBA can be used to measure the spatial intensity distribution of unattenuated, focused laser beams from high-power lasers.