Mainz 2026 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 77: Photonics – 3D Printing
Q 77.6: Talk
Friday, March 6, 2026, 15:45–16:00, P 2
Direct laser writing of in-volume diffractive optical elements with high speed and high resolution — Christian Ingenhag, Sebastian Stein, Aaron Schüller-Ruhl, and •Robert Fleischhaker — FH Aachen - University of Applied Sciences, Aachen, Germany
We report on a fast, high-resolution scheme to fabricate in-volume diffractive optical elements (DOEs) in fused silica by combining galvanometric beam scanning with a 0.4 NA microscope objective and a 1 ps laser. By exploiting nonlinear absorption and optimizing pulse energy for single-pulse writing, we achieve highly localized refractive-index modifications (Δ n ≈ 5· 10−2) and feature sizes below the nominal focal spot. A layer-stacking scheme in z produces multi-level phase masks: examples are a 4-level, 250x250 px DOE with 2 µm pixels and a 10-level, 416x416 px DOE with 1.2 µm pixels. Phase-contrast microscopy verifies the written phase profiles, which closely match theoretical designs. Optical tests at 532 nm reproduce target intensity patterns with high fidelity (overlap > 80% against the computed discretized mask in a selected region and > 66% versus the original target). Rapid fabrication times (60 s for the 4-level device, 8-9 min for the high-resolution DOE) improve the trade-off between quality and speed toward practical applications.
Keywords: diffractive optical element; direct laser writing; refractive index modification; galvanometric scanning of a microscope objective; phase-contrast microscopy