Additive manufacturing has recently become a key enabling technology in industrial fields, ranging from customized products for everyday usage to aerospace applications and small-batch industrial tooling. The future prospects extend up to the biofabrication of human organs. Ensuring the quality and repeatability of this process requires a systematic and comprehensive investigation of the underlying physical phenomena. In particular, melt-pool evolution is a critical feature, since irregularities in its spatial profile can influence microstructural evolution and weaken the integrity of the manufactured part. Microscale defects arising from balling and keyhole phenomena, often associated with recoil pressure, can severely degrade the quality of the resulting scanned track. This paper reviews the current state of optical approaches for melt-pool characterization and feature monitoring relevant to industrial laser additive manufacturing for process control and quality improvement, with a special focus on pyrometry and high-speed imaging. A single high-speed camera was generally used in experiments for melt-pool feature extraction, but two cameras were used to bypass emissivity values, which are otherwise difficult to obtain. Mathematical models were introduced to provide complementary information about melt-pool features, while artificial intelligence algorithms were used in other cases to process optical information. New melt-pool imaging databases and classifiers are expected in the near future to enable fast selection of appropriate process parameter windows, eliminating costly trial-and-error experiments.

We demonstrate a novel method for fabricating densely packed, high-aspect-ratio cavities (depth to diameter ratio > 1) in silicon wafers coated with diamond-like carbon (DLC). The process combines femtosecond laser irradiation with subsequent wet etch (potassium hydroxide-based) or plasma etch (chlorine- and oxygen-based). The femtosecond laser is used to pattern precise openings in the DLC layer, exposing the underlying silicon, which is then rapidly etched to form well-defined cavities. This combined laser ablation and etching approach enables high-throughput fabrication of densely packed micrometer cavities and offers scalability toward industrial production. The resulting hybrid DLC-coated silicon structure, featuring densely packed cavities, may exhibit antireflective properties in the far-infrared spectrum range.