Identification of nano-scale films for THz sensing
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There is a continued interest in the terahertz (THz) spectral range due to potential applications in spectroscopy and imaging. Real-time imaging in this spectral range has been demonstrated using microbolometer technology with external illumination provided by quantum cascade laser based THz sources. To achieve high sensitivity, it is necessary to develop microbolometer pixels using enhanced THz absorbing materials. Metal films with thicknesses less than the skin depth for THz frequencies can efficiently absorb THz radiation. However, both theoretical analysis and numerical simulation show that the maximum THz absorption of the metal films is limited to 50%. Recent experiments carried out using a series of Cr and Ni films with different thicknesses showed that absorption up to the maximum value of 50% can be obtained in a broad range of THz frequencies. A further increase in absorption requires the use of resonant structures. These metamaterial structures consist of an Al ground plane, a SiO2 dielectric layer, and a patterned Al layer. Nearly 100% absorption at a specific THz frequency is observed, which strongly depends on the structural parameters. In this paper, the progress in the use of thin metal films and metamaterial structures as THz absorbers will be described.
The article of record as published may be found at http://dx.doi.org/10.1117/12.918624
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