Review of in-situ process monitoring for ultra-short pulse laser micromanufacturing

Ultrashort pulse (USP) lasers enable machining of a wide range of materials, including hard and brittle materials such as steel, glass, silicon, and ceramics. Despite ongoing technological advances in USP laser micromachining systems, the lack of process repeatability and stability continues to hinder industrial adoption. This necessitates the development of innovative in-situ monitoring techniques capable of maintaining process stability and detecting early onset of anomalies. Besides, tight tolerances in micromanufacturing strongly require an automated, controlled, and regulated process. On the one hand, USP laser micromachining systems must be outfitted with in-situ sensing devices capable of measuring essential process signatures. On the other hand, in-process data analytics and statistical techniques are required to facilitate closed-loop process control. This paper provided a detailed literature review of in-situ monitoring of USP laser micromachining and other laser-based manufacturing processes. The mechanisms, advantages, limitations, signal processing methodologies and application in laser-based manufacturing techniques of different sensing techniques including acoustic, optical and image-based techniques are discussed. The techniques are reviewed with special focus on adaptability for USP laser micromachining towards automated process control, understanding process mechanisms and quality control.