Omnidirectional high-reflectivity mirror in the 4-20 m spectral range

Decreasing-width multilayers (DWMs) can behave as highly-efficient broadband reflectors with wider reflection spectrum than periodic, disordered or other aperiodic structures made of the same materials. In this article, we numerically analyze and optimize the reflectance R of a linear DWM formed by the bilayer CsBr - Te from normal to grazing incidence and for a large wavelength spectrum (from mid to far infrared). As a result, when the rate of the thickness decrease of CsBr layers equals −59.5 nm/layer, an optimized average reflectance for p polarization 〈 R p 〉 = 1 − 6 × 10 − 6 can be obtained in the 4-20 m spectral range for all angles of incidence. For s incident states, the average reflectance is even greater 〈 R s 〉 = 1 − 3 × 10 − 7 . Moreover, a near-zero transmittance region T ≤ 10 − 12 occurs in the 12-20 m wavelength interval constituting (to our knowledge) the widest spectrum for a single omnidirectional mirror where such remarkable reflectance values can be achieved.