Direct laser writing of in-volume diffractive optical elements with high speed and high resolution

We demonstrate fast, high-resolution fabrication of in-volume diffractive optical elements (DOEs) by combining galvanometric scanning with a microscope objective ( NA=0.4 ) and a 1 ps laser source. Carefully chosen parameters exploit nonlinear absorption in fused silica to create highly localized refractive-index modifications. Estimating the scaling laws of energy deposition, single-pulse writing becomes feasible, yielding a Δ n ≈ 0.5 × 10^ - 2 and modification dimensions below the nominal focal spot. Using a layer-stacking scheme in z , we assemble multi-level phase masks: examples include a 4-level, 250 × 250 px DOE (2 µm pixels) and a 10-level, 416 × 416 px DOE (1.2 µm pixels). Phase-contrast microscopy confirms the written phase structure and comparison with theoretical phase data shows strong correspondence. Optical characterization at 532 nm reproduces target intensity distributions with high fidelity (overlap $$>80$$ % against the computed discretized mask in a selected region; >66% vs. the original target). Yet, production times remain short (8–9 min for the high-resolution DOE, 60 s for the 4-level device), demonstrating that we improve trade-off between quality and speed to a level good enough for practical applications.