Quantitative study on optics and their alignment in laser material processing systems

Selection of optics and their alignment are too often taken for granted in the design and building of a laser material processing system. Traditionally the “measuring stick” is the process and whether it is working and not necessarily a quantitative value on the spot size and whether it has any aberrations. It is quite possible to have good optics and poor alignment and conversely have poor optics and good alignment and not immediately know that there is a problem at the process. Beam quality metrics have been around and in use for decades but have tended to be too bulky, expensive and hard to use for the average user. We study the impact of alignment and quality of typical optical components in a laser material processing system and the resulting impact at the focal spot. The consequence of decenter, tilted optics and commonly used beam enhancement devices like beam expanders are quantitatively investigated. The common optical aberrations of coma, astigmatism and spherical aberration are illustrated and correlated to the common alignment and optical selection mistakes. The importance of measuring the laser beam in both the near and far field using an all passive optical design beam metric system is further outlined.