Manipulation of Photonic Jets of Topological Gratings Comprising ITO Strips and Nanowalls Using Refractive Indices of Dielectric Nanofilms

This work proposes a quick measurement of the refractive index of dielectric nanofilm via a fabricated topological grating that comprises indium tin oxide (ITO) strips and nanowalls with an extremely high aspect ratio of 25. As the topological grating is capped with a dielectric nanofilm, the parabolic fields of the nanowalls destructively interfere with those of the ITO strips. This destructive interference weakens the photonic jets of the topological grating, decreasing its diffraction efficiency. The decrease in the diffraction efficiency determines the refractive index of the nanofilm without measuring its thickness in advance because the efficiency decrease is independent of the thickness. In other words, the photonic jets of the topological grating are manipulated by the refractive index of the nanofilm. The experimental results verify that refractive indices of titanium-dioxide, silicon-dioxide, and bovine-serum-albumin nanofilms with a thickness much smaller than the visible wavelengths can be measured by using the proposed topological grating. Therefore, topological gratings have great potential to develop advanced materials, fascinating devices, and innovative instruments.