Investigation of laser spot size and accuracy in laser speckle relative displacement estimation

As lasers become a commodity, there is a growing demand for affordable and precise position sensing in laser material processing. Digital Photonics is meeting this demand through a comprehensive development of system technology driven by photonics requirements. The focus lies on in-plane relative displacement sensing of a processing head in relation to a reference surface using laser speckle. This involves a template matching algorithm analyzing laser speckle images to track the template’s position in sequential images. The study investigates the impact of laser spot diameter on sensing accuracy by executing reference trajectories and continuously capturing images at fixed gain and exposure time. Employing normalized cross-correlation template matching and a calibrated rotation matrix, displacement is calculated. The results indicate an increasing estimation accuracy with varying spot size (1 mm to 9 mm), revealing a minimum spot diameter of 3 mm with a corresponding maximum estimation error of 0.077 mm. The setup demonstrates simplicity and accuracy, making it highly promising to enable future digital photonic systems. 114 technik und Messsysteme