Light-shielding film on edges and draft facets of Fresnel lens fabricated by picosecond laser processing

We present a way to prevent stray light generated from draft facets of Fresnel lens. Fresnel lens has distinctive shape that induces stray light. The draft facets can generate as much as 8% of stray light, deteriorating performance of optics. To prevent such stray light, we fabricated light-shielding film on draft facets and edges of Fresnel lens. First, we investigated structure and material of the shielding film. We then studied optimal laser source which can perform the precise processing, and found that laser ablation by picosecond laser works the best. Finally, we demonstrated the fabrication of light-shielding film on draft facets of Fresnel lens by experiment, and verified the elimination of stray light.