Wave optical model for tomographic volumetric additive manufacturing

Tomographic Volumetric Additive Manufacturing (TVAM) allows printing of mesoscopic objects within seconds or minutes. Tomographic patterns are illuminated onto a rotating glass vial which contains a photosensitive resin. Current pattern optimization is based on a ray optical assumption which ultimately leads to limited resolution around $20\mu\textrm{m}$ and varying throughout the volume of the 3D object. In this work, we introduce a rigorous wave-based optical amplitude optimization scheme for TVAM which shows that high-resolution printing is theoretically possible over the full volume. The wave optical optimization approach is based on an efficient angular spectrum method of plane waves with custom written memory efficient gradients and allows for optimization of realistic volumes for TVAM such as $(100\mu\textrm{m})^3$ or $(10\textrm{mm})^3$ with $550^3$ voxels and 600 angles. Our simulations show that ray-optics start to produce artifacts when the desired features are $20\mu\textrm{m}$ and below and more importantly, the amplitude modulated TVAM can reach micrometer features when optimizing the patterns using a full wave model

Holographic Volumetric Additive Manufacturing

3D printing has revolutionized the manufacturing of volumetric components and structures in many areas. Different technologies have been developed including light-induced techniques based on the photopolymerization of liquid resins. In particular, a recently introduced method, so-called Tomographic Volumetric AM (VAM), allows the fabrication of mesoscale objects within tens of seconds without the need for support structures. This method works by projecting thousands of amplitude patterns, computed via a reverse tomography algorithm, into a resin from different angles to produce the desired three-dimensional shape when the resin reaches the polymerization threshold. To date, only amplitude modulation of the patterns has been reported. Here, we show that holographic phase modulation unlocks new capabilities for VAM printing. Specifically, the effective light projection efficiency is improved by at least a factor of 10 over amplitude coding; the resolution can reach the light diffraction limit; and phase encoding allows to control ballistic photons in scattering media, which potentially increases the volume of 3D objects that can be printed in opaque and non-absorbing resins. The approach uses CGH to convert phase, encoded on a 2D modulator to the desired intensity projections by light propagation in a photosensitive resin container. We demonstrate the potential of holographic phase coding using simulations and experiments, the latter by implementing a volumetric printer using a DMD, as the 2D phase modulator in a Fourier configuration. Specifically, we use Lee holograms to encode phase onto a binary DMD. Combining tiled holograms with PSF shaping mitigates the speckle noise typically associated with computer-generated holograms and speed-up their computation. We use these holographic projections to fabricate millimetric 3D objects in less than a minute with a resolution down to 164 um