Graphene-based optical absorbers in middle-infrared wavelengths

In the visible and near infrared regions, graphene is essentially transparent with a constant absorptivity of 2.3%. On contrast, in longer wavelengths, the absorptivity can be enhanced by graphene plasmons motivated by simple nanostructures. Besides, the graphene plasmons can be further enhanced via electrostatic doping when voltage is applied. This work numerically demonstrates that in optimized configuration the absorptance in monolayer graphene can be greatly enhanced and reach to 98.6% of the impinging light for transverse magnetic (TM) polarizations. Graphene can interact with light via plasmonic resonance. Towards this, we utilize a subwavelength-thick optic cavity, which composed of graphene grating, a dielectric spacing layer and a metal film to further enhance the interaction. When we use the TM mode source, the incident light matched the graphene plasmons, a strong drastic cut in the energy of the reflected light, which means obvious resonance absorption occurred. Meanwhile, the reflection can approach 0 when voltage applied. Finally, great absorption in 6.94 μm has been achieved by the graphene grating with the addition of a subwavelength-thick optic cavity via different voltage.

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