Fig. 3

Comparison of normalized propagation length (top) and material confinement (bottom) of SPP on selected semiconductors and noble metals. The gaps in the curves are caused by either the phonon (semiconductor) or band absorptions (Au, Ag), where the real part of permittivity is greater than -1. The x-axis is the logarithmic scale of wavenumber, 10⁴ cm ⁻¹ corresponds to wavelength of 1 μm. The y-axis is normalized to the wavelength used (λ), i.e. a number of wavelengths the SPP propagates before decaying to 1/e. Data for Au and Ag were taken from [33]. Highlighted areas w ₀- w ₄ show the bands of THz radiation considered for communications applications due to atmospheric absorptions [2, 3], compared to the infrared C band and visible light