High-speed time-domain characterization method for polygon scanners

Two major advantages of polygon scanners over galvano scanners are their fast scanning speed and linear scanning motion. However, a polygon scanner has a fundamental problem associated with the irregularity of its structure due to unequal facet-to-facet angles. Conventional methods rely on geometrical measurements of the polygon mirror structure; though accurate, they are time-consuming and do not show other scanning errors in the real beam scanning action. We propose a simple and fast time-domain characterization method that can show the structural defects of a polygon mirror as well as other scanning jitter that exists only when it is in motion. A laser beam's optical power passing through a slit is measured using a fast detector and digitizer. By analyzing repeated pulse patterns in the data, we can estimate facet-to-facet angles and other scanning jitter of a polygon mirror. Our proposed method is experimentally demonstrated by measuring three polygon mirrors with 12 facets.