Laue photonic crystals integrated in the bulk of sapphire

We report controllable, crack-free volumetric phase inscription in sapphire by switching femtosecond direct laser writing from the near-IR to the deep-UV (fourth harmonic, 257 nm), and validate the approach by fabricating Laue-type photonic-crystal (PhC) spatial filters. The UV-fs inscription with the beam incident along the M axis, scanning along the C axis, and polarization along the A axis widens the modification window and suppresses stress-driven failure that typically plagues IR laser-patterning in hard, brittle crystals, enabling densely packed 3D phase elements at the millimeter scale. We produce multi-layer Laue PhCs with a 3 mm clear aperture and ∼ 2.88 mm 3 beneath the surface, without fracture or edge spallation. Quantitative polarimetric imaging confirms low residual strain at structure boundaries, consistent with stable volumetric modification. The observed transmittance modulation follows a simple per-layer scattering-parameter (phase-screen) model, allowing predictive scaling with structure thickness and fluence. This UV-enabled DLW route thus delivers, to our knowledge, the first functional Laue PhCs in sapphire, with a crack-free 3 mm aperture, and opens a route to large-aperture phase elements in a crystalline host for high-intensity and nonlinear photonics.