Experimentation in bulk laser processing — the cutting, drilling, engraving, or other structural modification of dense material using high-powered, high-f requency pulse duration “ultrafast” lasers — is the focus of recent experiments at two schools within the Friedrich Schiller University of Jena in Jena, Germany: The Institute of Applied Physics (IAP) and the Abbe Center of Photonics (ACP). The goal of these experiments was to select or build a lens whose properties offset the aberrations that are unique to a specific optical design. Using an open-source solution, the team was successful in the design and development of high-quality laser systems that can reliably process bulk objects with a minimum of variation error.
Successful laser processing depends on accurate prediction of the optical field distribution of the laser’s focus. Some laser processing system components can introduce aberrations (distortions) in the laser beam that elongate the focal position of the beam beyond its intended circular presentation. As a result, a reduced level of precision is created by effectively shifting or dispersing the laser’s intended path. Stock lenses often produce aberrations that are within the margin of tolerance for standard optical systems, but not for high-powered lasers. In many optical applications, customizing the light source helps compensate for these aberrations. For laser systems, that isn’t an option. During processing, focus material (called the “bulk”) can also produce spherical aberrations that affect precision — particularly when processing thick objects.
To solve these challenges required selecting or building a lens with properties that offset aberrations unique to a specific optical design. Ray tracing analysis was conducted on proposed designs at each step of development to find factors that would yield a system with the precision required to process brittle materials. The team used ray tracing algorithms in OpticStudio, then selected the processing condition to test specific system parameters — including lens, processing depth, and spatial light modulator offset — that featured negative aberrations and offset aberrations quantified during OpticStudio analysis.