Millimeter-Scale Diffractive Optical Elements Fabricated by Two- Photon Polymerization for Beam Shaping in Materials Processing

Beam shaping is a crucial aspect in the field of laser materials processing.Among the optical elements available for this purpose, Diffractive Optical Elements (DOEs) stand out due to their robustness and versatility.However, a flexible fabrication method is desirable to facilitate rapid testing of different beam shapes using various DOEs.Two-Photon Polymerization (2PP) is a promising fabrication technology for this purpose, as it allows the creation of arbitrarily shaped three-dimensional structures with a resolution down to 100 nm and excellent surface quality.In this work, a DOE was fabricated using 2PP, which modulates the light into a set of two ring beams.The phase input was calculated as a computer-generated hologram using the prism and lens algorithm, where the term for the axial focus shift was substituted by an axicon hologram.The DOE has a diameter of 3.5 mm and a maximum height of 6.4 m.To fabricate this DOE, the phase input image was converted into a corresponding three-dimensional STL file depending on the gray level of each hologram pixel.After fabrication, beam shaping properties of the DOE were analyzed using a beam profiler to visualize the resulting two ring beams.Damage threshold experiments validated the robustness of the DOE for material processing.