Abstract
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...
Highlights
The field of surface nanostructuring is growing rapidly with the need to search for more advanced fabrication solutions
Multipulse irradiation causes the material to reorganize into laser-induced periodic surface structures (LIPSS) at micro- and nanoscale, which was observed on virtually any type of media such as metal, semiconductor, dielectric solids, and thin films,[7] including indium tin oxide (ITO) film.[8−11]
At the pulse energies slightly above the ablation threshold, the ITO film is modified along its depth organizing into periodic structure that is qualitatively dependent on the laser material processing conditions
Summary
The field of surface nanostructuring is growing rapidly with the need to search for more advanced fabrication solutions. Almost two decades ago it was demonstrated that femtosecond laser pulses focused inside silica glass can lead to selfassembled nanogratings,[12,13] which exhibit birefringence comparable to quartz crystals.[14] Later, this anisotropy in silica was engineered to surface nanogratings showing a 3-fold birefringence increase.[15] the laser-induced birefringence is high enough for realization of various functional elements, the resultant thickness of nanostructures limits its performance in flat optics.[2] Recent experimental investigations revealed 2 orders of magnitude higher birefringence in amorphous silicon[16,17] and silicon carbide[18] films, suggesting that the high-refractive-index materials could be used for fabricating anisotropic surfaces. The control of orientation and strength of nanostructuring is achieved within a submicron thickness realizing the fabrication of space-variant polarization sensitive optical elements, polarization, and intensity multiplexed optical data storage
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