Knife-edge lateral scanning method for automated measurement of wavefront power spectral density

In high-power laser systems, mid- to high-frequency errors in optical elements can significantly degrade beam quality, potentially leading to filamentation, which increases the risk of damage to optical components and reduces system efficiency. Power spectral density (PSD) is a critical metric for assessing surface wavefront errors in optical elements. The PSD of the components was ensured through iterative processing and measurements. Currently, PSD detection primarily relies on interferometry. However, its stringent stability requirements make efficient online measurements challenging. A knife-edge lateral scanning method is proposed that enables an efficient and automated PSD detection of large-aperture optical components. The equivalent relationship between shadowgraph PSD and wavefront PSD is established in this method, which allows for the direct calculation of the PSD curve from the shadowgraphs. It reveals periodic modulation by laterally blocking higher-order light spots. The scanning and image-stitching techniques in this approach eliminate the need to determine the knife-edge cutting position, thus making the measurement process more convenient. The experimental results indicate an RMS error of approximately 5%. This method lays the foundation for rapid online PSD detection, which has significant implications for the efficient iterative processing of high-precision optical components.