High-speed speckle averaging for phase-only beam shaping in laser materials processing. (June 2023)

• Record Type: Journal Article
• Authors: Ackermann, Lisa; Roider, Clemens; Gehring, Matthias; Cvecek, Kristian; Schmidt, Michael
• Is Part Of: Optics and lasers in engineering. Volume 165(2023)
• Publication Date: 2023-06
• Subjects: LCoS SLM -- Phase-only beam shaping -- Speckle averaging -- Ultrashort pulsed laser materials processing; Lasers in engineering -- Periodicals; Optical measurements -- Periodicals; Optics -- Periodicals; Lasers en ingénierie -- Périodiques; Mesures optiques -- Périodiques; Optique -- Périodiques; 621.36605
• DOI: 10.1016/j.optlaseng.2023.107537
• Languages: English
• ISSNs: 0143-8166

Abstract

Highlights: near-perfect speckle averaging with a single phase mask on a liquid crystal on silicon spatial light modulator (SLM). high light efficiency through kHz averaging by scanning the beam with a galvanometer scanner over the SLM. high feasibility and easy to set up → possibility for implementation in industrial applications. analysis of ultrashort pulsed laser material interaction where the lateral intensity information can be adapted from pulse to pulse. Graphical abstract: Abstract: A phase-only spatial light modulator (SLM) is a powerful tool to shape arbitrary intensity distributions and finds application in various research fields and industry. However, since phase-only beam shaping cannot control the full complex light field, a speckle pattern overlays the shaped target intensity and strongly impairs the result. Several methods have been developed to diminish speckle noise, all of which have their advantages and disadvantages. Usually they offer a compromise between quality and efficiency. We present a method for phase-only beam shaping which achieves near-perfect and highly efficient speckle averaging with a liquid crystal on silicon SLM based on a single phase mask. A galvanometer scanner scans the laser beam over the active area of the SLM to achieve high-speed averaging. The applied angle resulting from the scanning movement is compensated by a proper optical setup to maintain a static target image with speckle averaging out. As an additional benefit of the scanning movement, artifacts from light not diffracted by the SLM disappear in the target plane. The setup is designed for high-energy laser beams as intermediate foci are avoided at all optical components. Besides optical averaging on camera images, we validate our method with ablation experiments where we make a profound analysis of the involved system parameters and the achieved quality. Thereby, it becomes apparent that the proposed method not only stands out by the high-quality results but also by its simplicity in implementation.