(438c) Blade-Coating and Sintering of Mesomorphic Ceramics

Transparent and birefringent inorganic films are demanded for polarization control of high power lasers. While cut and polished single crystals or films obtained via glancing angle deposition sputtering methods can exhibit desirable optical properties and laser damage resistance, these methods suffer in cost and scalability. Mesomorphic ceramics as inorganic polycrystalline solids with static liquid crystalline superstructure offer appealing transparency and birefringence for polarization control. However, the poor mechanical robustness and optical scattering in sintered mesomorphic ceramic films may limit their performance in high-power laser systems. Here, we report on the fabrication and characterization of novel ZnO mesomorphic ceramics to evaluate how thermal sintering affects optical properties, mechanical strength, and laser damage resistance.

Colloidal suspensions of ZnO nanorods were blade-coated onto glass slides to create uniform and transparent coatings of aligned nanoparticles, and thermal sintering was conducted at different temperatures, ramp rates and sintering times. Sintering accomplished crystallite growth, neck growth, and densification while preserving the uniaxial orientation of ZnO crystallites. The extent of sintering for different thermal treatments was quantified by morphological changes, and activation energies for neck growth by surface diffusion and densification by boundary diffusion could be estimated. After sintering, the anisotropic morphology retains in-plane optical birefringence and the Young’s modulus and hardness show an exponential dependence on the measured film porosity. A mesomorphic ceramic films sintered at 600 °C for 2h retained transparency and high birefringence (T > 90%, ∆n = 0.12 at 600-1690 nm) and exhibited higher modulus (E = 36 GPa). The laser-induced damage threshold of sintered films determined using a Nd:YAG laser (1064 nm) will be discussed as well.