Wideband perfect light absorber at midwave infrared using multiplexed metal structures

Abstract

We experimentally demonstrate a wide band near perfect light absorber in the mid-wave infrared region using multiplexed plasmonic metal structures. The wide band near perfect light absorber is made of two different size gold metal squares multiplexed on a thin dielectric spacing layer on the top of a thick metal layer in each unit cell. We also fabricate regular nonmultiplexed structure perfect light absorbers. The multiplexed structure IR absorber absorbs above 98% incident light over a much wider spectral band than the regular non-multiplexed structure perfect light absorbers in the mid-wave IR region.Anomalous light absorption in metal structures was first observed a century ago by Wood [1]. The interest of light absorption in structured metals resurfaced in the 1960s, 1970s, and 1990s [2-8]. Today, it is well understood that anomalous light absorption in metal structures is due to the excitation of surface plasmon-polaritons (SPPs). Recently, perfect electromagnetic energy absorptions in structured metamaterials have been demonstrated in the gigahertz and terahertz regimes [9][10]. Perfect absorbers at optical frequencies have also been reported by several groups [11][12][13][14][15][16]. However, all the metamaterial perfect absorbers reported have very narrow spectral widths limited by the line-widths of the electromagnetic resonances in the structures. In many applications, it is desirable to have perfect absorption over broader spectral bands. Expansion of absorption band has been proposed using structures combining multiplexed subwavelength apertures [13], however, the proposed structure is polarization dependent and experimentally has not been demonstrated. In this paper, we report an experimental demonstration of a wide spectral band perfect absorber using a multiplexed surface plasmon resonance structure. In the multiplexed surface plasmon resonance structure, two gold metal squares are multiplexed in the unit cell of the periodic structure. The multiplexed plasmonic structure metamaterial, operating in the mid-wave infrared regime, near perfectly absorbs photons over a wider spectral range than previously reported.Figure 1 (a) shows the regular non-multiplexed narrow band perfect light absorber structure. In this structure, gold thin film squares are patterned periodically on the top of a thin dielectric layer deposited on top of a thick gold metal layer. The thick metal layer is thick enough that no transmission can occur when light is incident from above the structure. Due to electromagnetic resonance in the metal-dielectric subwavelength structure, the effective impedance of the structured metamaterial surfaces can match the impedance of the vacuum; therefore reflections from the surface can be completely eliminated. Fig. 1 (b) shows the multiplexed perfect light absorber structure. The period of the multiplexed structure is the same as the period of the non-multiplexed perfect light absorber structure.However, in the multiplexed structure there are two metal squares of different sizes in the un...

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