Visible transparent mid-infrared broadband absorbers based on gradient refractive indexes and multi-size cavity resonances

We proposed a multi-layered nanorod structure with the same tilt angle and different diameters, which has high visible transmittance and strong 3-5 mu m absorption based on the principles of the gradient of the refractive index and the multi-size cavity resonances. The indium tin oxide (ITO) was selected as the target material to fabricate the structure by using a glancing angle deposition method. The experimental results show that when the deposition angle theta is 80 degrees, swing deposition is successively done with the rotation angle yo of +/- 8 degrees, +/- 5 degrees, +/- 3 degrees, and 0 degrees on the surface of the substrate, and the quartz crystal microbalance thicknesses of ITO nanorods are 220 nm for each deposition, the average transmittance is 80.5% in the range of 400-800 nm and the integrated absorption is 86% in the 3-5 gm band. Such a simple, low-cost, and easy-to-fabricate device has potential applications in window stealth materials and other related fields. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement