Design of CNT-based perfect absorbers over SWIR to LWIR frequencies for sensing applications

Abstract

Carbon nanotubes (CNT) are known for their use in solar thermal technologies due to their high absorption across the solar band. We design structural arrays of circular shaped CNT disc on conducting metallic film (Ag) that give rise to specified absorption bands at short-wavelength infrared (SWIR) to long-wavelength infrared (LWIR) frequencies. We note that nearly 99 % of absorbance occurs at the wavelength of 11.8 μm in the absorbance spectrum. In addition to that, other two peaks are at the wavelength of 5.6 μm and 7.8 μm with nearly 70 % and 80 % of absorbance respectively. The high absorbance at the wavelength of 11.8 μm is primarily due to the dipolar resonance while other peak positions in the spectrum are due to the higher mode and the vertical cavity mode resonances. Further, it is been shown that the simple design of CNT based perfect absorber can be used as sensing application at the infrared frequencies.