Ultra-wide Band, Polarization-Independent, Omnidirectional Absorbers

Based on the effective medium theory for multilayers, we present the design of several all-angle, polarization-insensitive absorbers spanning the visible, near-IR and part of the mid-IR (from 400nm to 3500nm) using periodic, one-dimensional, metallo-dielectric structures. OCIS codes (310.4165) Multilayer design; (310.3915) Metallic, opaque, and absorbing coatings. Visible and IR absorbing materials are crucial in many applications such as thermo-photovoltaic energy conversion devices [1] and light harvesting for solar cells [2]. Many venues have been proposed during recent years to achieve broadband, polarization-insensitive, omni-directional absorbers. In [3] the authors experimentally demonstrate an ultrathin plasmonic absorber over the entire visible spectrum (400nm-700nm), in [4] the authors numerically study a broadband, 1-D metal grating with almost perfect absorption at λ~600nm, in [5] an absorber based on light propagation in a metamaterial forming an effective “black-hole” is discussed, and in [6] it is proposed a negative-index based, wide angle absorber for IR radiation. In this work we propose a viable, yet effective, alternative to achieve an efficient absorber for visible and near IR radiation. The generic structure under consideration is depicted in Fig.1. It consists of an N-period multilayer made of two different, generic, non-magnetic, materials with thickness respectively a and b=Λ-a and electric permittivity εa and εb respectively. Figure 1: Generic multilayer structure with period Λ made of two different materials. It is well known [7] that when the wavelength λ of the incident radiation is much longer than the thickness of the elementary cell (λ>>Λ) the multilayer behaves as an effective, uniaxial crystal with effective ordinary (o) and extraordinary (e) permittivity given by: