Auto-focus methods in laser systems for use in high precision materials processing: A review

High-precision focusing for laser systems has played an essential role in materials processing. Over the last few decades, the auto-focus (AF) mechanism has grown in popularity, providing numerous rapid and precise auto-focusing systems that have been launched and extensively installed in control systems with lasers. Several approaches for laser technology, when embedded in a system, may deliver the best laser focus to the users in a matter of seconds, freeing users from manual focusing. The AF system has matured in terms of both technology and market within years of development. These systems are developed on the basis of different mechanisms including optical-based, image-based, acoustic signal-based, and plasma-based methods. Furthermore, besides analyzing the focus detection techniques, methods for controlling the laser focal position are also discussed. This article provides an overview of these auto-focusing techniques in laser systems for use in measurements and materials processing as well as the use of deformable optics in controlling laser focal position.