Form-Birefringence in ITO Thin Films Engineered by Ultrafast Laser Nanostructuring

The field of surface nanostructuring is growing rapidly with the need to search for more advanced fabrication solutions. The major challenge is the lack of appropriate combination of time/cost efficient techniques and medium possessing the advantages of both flexibility and tunable optical properties. Here we demonstrate direct-write femtosecond laser nanostructuring of indium-tin-oxide thin film where the deep-subwavelength ripples with periodicity of down to 120 nm are realized originating the form birefringence (|Δn| ≈ 0.2), which is 2 orders of magnitude higher than the commonly observed in uniaxial crystals or femtosecond laser nanostructured fused quartz. The demonstrated nanoripples with its continuously controlled space-variant orientation lead to the high density two-dimensional printing of flat optical elements. The technique can be extended to any highly transparent films that support laser-induced periodic surface structures, and can be effectively exploited for the integration of polarization sensitive modifications into multidimensional optical data storage.