Description
Large-aperture, high-threshold phase optics are needed for beam transport and nonlinear experiments at high-intensity laser facilities. We demonstrate crack-free volumetric inscription of Laue-type photonic-crystal spatial filters [1,2] in sapphire using fourth-harmonic femtosecond direct laser writing at 257 nm. Deep-UV two-photon absorption combined with crystallographically defined writing (k ∥ M, vscan ∥ C, E ∥ A) widens the modification window and suppresses stress-driven cracking that limits near-infrared writing in brittle crystals. Multilayer structures with a 3 mm clear aperture and ~2.88 mm³ modified volume were fabricated beneath the surface without fracture or edge spallation. Polarimetric imaging shows low residual strain at boundaries, while optical measurements confirm resonant angular attenuation and predictable fluence- and layer-dependent filtering. The method enables robust embedded sapphire optics for spatial filtering, beam shaping and high-power nonlinear photonics.
[1] S. Gawali, D. Gailevičius, G. Garre-Werner, V. Purlys, C. Cojocaru, J. Trull, J. Montiel-Ponsoda, and K. Staliunas, "Photonic crystal spatial filtering in broad aperture diode laser," Appl. Phys. Lett. 115(14), 1–5 (2019).
[2] D. Gailevičius, V. Purlys, and K. Staliunas, "Photonic crystal spatial filters fabricated by femtosecond pulsed Bessel beam," Opt. Lett. 44(20), 4969 (2019).
