Single-Photon TVAM: Rapid Volumetric 3D Printing

• Single-photon TVAM is a volumetric 3D printing strategy that uses patterned 405 nm light to photopolymerize resin throughout a volume, achieving tens-of-micrometer resolution.
• The process relies on precise optical design and dose calculations to control crosslinking in targeted voxels while minimizing exposure in void regions.
• Hybrid integration with Two-Photon Polymerization enhances multiscale fabrication, enabling sub-micrometer features on rapid, millimeter-scale substrates without additional resin changes.

Single-photon Tomographic Volumetric Additive Manufacturing (TVAM) is a photopolymerization-based 3D printing strategy characterized by rapid volumetric fabrication of millimeter- to centimeter-scale objects with tens-of-micrometer feature resolution. By illuminating a static photopolymer resin from multiple angular projections using patterned single-photon (typically 405 nm) light, TVAM achieves simultaneous crosslinking throughout the desired volume, departing from conventional layer-by-layer workflows. Recent advancements demonstrate integration of TVAM with Two-Photon Polymerization (2PP) for routine hybrid multiscale fabrication, synergizing sub-µm and mm-scale precision within unified workflows without resin switch or intermediate post-processing (Unlu et al., 19 Jan 2026).

1. Physical Principles of Single-Photon TVAM

Single-photon TVAM employs volumetric photopolymerization mediated by photon absorption. A photopolymer resin—commonly DUDMA:PEGDA (4:1 w/w) with 1.35 wt.% TPO-L—is statically contained in a quartz vial (n=1.4696, φ_i=4.30 mm), illuminated from projection angles θ∈[0,2π) by patterned 405 nm CW light. Photoinitiator molecules absorb photons, generating free radicals which then trigger chain polymerization. Polymerization occurs where the local accumulated energy dose $D(x,y,z)$ surpasses the threshold $D_{th}$ (≈45 mJ cm^−3), yielding a stable, volumetric crosslinked network.

Light transport is governed by Beer–Lambert attenuation:

$$dI/ds = -\alpha I(s) \implies I(s) = I_0 e^{-\alpha s}$$

with linear absorption coefficient $\alpha = 1.081$ mm^−1 at 405 nm. Dose per voxel $v$,

$$D_v = \sum_{p,\theta} \int_0^{L_{v,p,\theta}} \alpha I_{p,\theta}(s) ds$$

where $I_{p,\theta}(s)$ is the ray intensity from DMD pixel $p$ at angle $\theta$; $L_{v,p,\theta}$ is the path-length within voxel $v$.

2. System Implementation and Optical Architecture

The optical system comprises a fiber-coupled 405 nm CW laser diode (P_max≈36–70 mW), spatial light modulation (V-7000 VIS DMD), and achromatic doublet lenses (f_1=300 mm, f_2=150 mm) to demagnify and spatially filter $N_{proj}$ patterns prior to projection. The resin vial mounts on a motorized rotation stage. Print geometry is realized by synchronizing rotation and pattern display: for $N_{proj}$ projections, vial angular velocity $\omega$ provides a per-projection display time $\Delta t = T_{rot}/N_{proj}$ (e.g. $T_{rot}=12$ s, $N_{proj}=360$ results in $\Delta t \approx 33$ ms).

The spatial resolution is predominantly determined by the optical point spread function (PSF); Zemax ray-trace yields RMS diameter ≈6.8 µm, with empirical minimum feature size ≈20 µm for mm-scale objects. Overprinting onto a glass rod (n=1.4814, d=1.0 mm) allows post-TVAM access with high-NA objectives for subsequent 2PP.

3. Mathematical Framework: Dose Calculation and Pattern Optimization

Light propagation is discretized: each DMD pixel at each projection angle casts a ray through the resin, modeled by a ray-tracing engine ("Dr.TVAM," Editor's term).

Absorbed energy in voxel $v$ from pixel $p$ at angle $\theta$:

$$\Delta D_{v,p,\theta} = I_{p,\theta}^{\,\text{in}} (1 - e^{-\alpha \Delta s})$$

where $\Delta s$ is voxel step length; $I_{p,\theta}^{\,\text{in}}$ is entering ray intensity. Total voxel dose:

$$D_v = \sum_{\theta=1}^{N_{proj}} \sum_{p} \Delta D_{v,p,\theta}$$

Inverse optimization seeks projection patterns $P_{p}^{(k)} \in [0,1]$ maximizing $D_v$ in target voxels $V_{obj}$ and minimizing it in voids $V_{void}$, subject to bounds:

$$L = W_{in} \sum_{v \in V_{obj}} \text{ReLU}(D_{th,u} - D_v)^2 + W_{out} \sum_{v \in V_{void}} \text{ReLU}(D_v - D_{th,\ell})^2 + W_o \sum_{v \in V_{obj}} \text{ReLU}(D_v - D_{max})^2 + W_{sparsity} \sum_{p,k} (P_{p}^{(k)})^2$$

where $D_{th,\ell}$ and $D_{th,u}$ are dose bounds; $D_{max}$ penalizes overexposure; $W_{sparsity}$ enforces energy conservation.

Angular sampling $\Delta \theta = 2\pi/N_{proj}$ follows the Nyquist limit, requiring $N_{proj} \geq \pi D_{object}/\delta_\theta$ for reconstructing features of size $\delta$. Exposure duration and laser power linearly scale delivered dose.

4. Polymerization Kinetics and Resin Parameters

Photoinitiation rate is expressed as $R_i = \Phi \alpha I_0$ (with quantum yield $\Phi$); radical concentration $[R^\bullet](t)$ increases until gelation. Polymerization rate $R_p = k_p [M][R^\bullet]$; $[M]$ monomer concentration, $k_p$ propagation rate constant. Gelation requires $D_{th} \approx 45$ mJ cm^−3.

Higher TPO-L concentration enhances $\alpha$, affording greater lateral confinement but diminishing build height. Oxygen inhibition is largely mitigated by high radical flux; single-photon volumetric curing exhibits reduced oxygen sensitivity compared to surface SLA. Resin viscosity (η ≈ Pa·s) influences flow during rotation; approximately three full turns pre-print ensure uniformity and minimize shear distortion.

5. Performance Metrics and Operational Trade-offs

TVAM Alone

• Minimum resolvable feature: ≈20 µm
• Volumetric throughput: 0.1–1 mm³/s (e.g., 1.1 mm × 1.1 mm × 1.1 mm gear in 12 s yields ≈0.11 mm³/s)
• Enhanced resolution via increased $N_{proj}$ or reduced PSF with higher NA optics; trade-off with print time or field size

Hybrid TVAM + 2PP

• TVAM: mm-scale substrate in ~12 s (20 µm features)
• 2PP: localized sub-µm features (270 nm axial, <100 nm lateral) with SLM-limited rates ≈20 voxels/s
• QR-code print: ~882 voxels, 50 ms/voxel ≈44 s
• Projected 2PP acceleration (resonant scanners): up to $2\times10^7$ voxels/s, feature time down to milliseconds per 100 µm pattern

Trade-Offs

TVAM alone is optimal for rapid coarse structures (>20 µm), while hybridization extends resolution to sub-µm with minimal local time investment. Unified process involves no resin change or post-processing, streamlining throughput.

6. Integration with Two-Photon Polymerization

TVAM generates mm-scale "blanks" attached to a rotating glass rod. Without dismounting, the rod is translated so that a 780 nm fs-laser (70 fs, 80 MHz) focuses through a 20×/NA 0.45 objective onto desired regions. SLM steers single or multi-voxel patterns (hatching=760 nm, slicing=0.8–1.2 µm, $P_{IR}$=13–18 mW, $t_{exp}$=50 ms) to effectuate sub-µm features.

Because the substrate is pre-polymerized, 2PP writes above a solid volume, reducing focal distortion and oxygen quenching. Refractive-index contrast between TVAM-printed and 2PP regions (n_resin ≈ 1.4827 vs. n_2PP-polymer ≈ 1.48–1.52) suffices for micro-optical functionalities, with negligible aberration—an outcome supported by Dr.TVAM’s refraction-aware modeling.

7. Experimental Demonstrations and Application Domains

Millimeter-Scale Gear with QR Code

• Gear: 1.1 × 1.1 × 1.1 mm, 225 µm overprint height (TVAM), dose = 45.3 mJ cm^−3, T = 12 s
• QR code: 2 layers, 270 nm axial, ~500 nm lateral, 13 mW IR, 50 ms/voxel
• SEM imaging validates ~270 nm features

Bridge-Like Structure on Stacked Prisms

• Stacked TVAM prisms: 1.1×1.1×0.85 mm & 0.68×0.68×0.45 mm, lateral holes, 275 µm overprint, dose = 51.3 mJ cm^−3, T = 12 s
• 2PP bridge: 36×36×28 µm legs, 15×15×4 µm top hole, 18 mW IR, 50 ms/voxel, hatching = 760 nm, slicing = 1.2 µm, 23 layers
• SEM and phase-contrast microscopy confirm sub-µm fidelity

Continuous-Rotation 2PP

• Rod rotated at 2°/s and fixed fs-beam enables circular inscription (Ø ≈ 168 µm) written in two turns, realizing helical 2PP

Applications span bioscaffolds and tissue engineering (where tens-of-µm features suffice over bulk volume, with sub-µm confined to functional regions), as well as micro-optics (waveguides, microlenses), leveraging refractive-index contrast between 2PP and TVAM domains.

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Single-photon TVAM furnishes a reproducible pathway for rapid, scalable 3D microfabrication, especially when compounded with localized 2PP for multiscale precision. The described equations, dose-thresholding logic, ray-tracing inverse design, resin composition, and system parameters constitute an experimentally validated scheme suitable for continued innovation and deployment in advanced additive manufacturing contexts (Unlu et al., 19 Jan 2026).