Abstract
The optical performance of high-resistivity silicon with a laser-ablated surface was studied in the transmission mode in the frequency range of 0.1–4.7 THz. A reciprocal relationship between the transmission brightness and the surface roughness was observed at discrete THz frequencies. The measured dispersion was reproduced by the THz wave scattering theory using an effective refractive index model. No significant differences between the samples processed either with ps- or ns-duration laser pulses in ambient air or in argon enriched atmosphere were found in the THz regime. It was demonstrated that the majority of optical losses of the silicon with the laser modified surface were due to the scattering of THz waves and not due to the absorption in silicon-compounds formed during the laser ablation.
Highlights
E LECTROMAGNETIC waves of terahertz (THz) frequency gain more attention from scientists and engineers due to new emerging applications of THz imaging in astronomy, medicine, art conservation, security, materials inspection, etc. [1]–[5]
The silicon was laser-ablated into a depth of about 30 ± 4 μm in order to develop a rough surface with an area of 6 × 6 mm2
The THz performance of the samples was investigated in the transmission mode in the frequency range from 0.1 to 4.7 THz using THz imaging and THz time-domain spectroscopy (THz TDS) systems described elsewhere [6], [9], [11]
Summary
E LECTROMAGNETIC waves of terahertz (THz) frequency gain more attention from scientists and engineers due to new emerging applications of THz imaging in astronomy, medicine, art conservation, security, materials inspection, etc. [1]–[5]. E LECTROMAGNETIC waves of terahertz (THz) frequency gain more attention from scientists and engineers due to new emerging applications of THz imaging in astronomy, medicine, art conservation, security, materials inspection, etc. Off-axis parabolic mirrors and refractive lenses are available commercially and very often are employed in THz imaging setups. Compact diffractive lenses such as multilevel phase Fresnel lenses (MPFLs) and Fibonacci lenses have been developed on high-resistivity silicon (HR-Si) in order to reduce the complexity of the THz systems [6]–[9]. Silicon MPFLs have been fabricated using photo-lithography and the reactive ion etching technique [7].
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