Terahertz diffractive structures for compact in-reflection inspection setup
Siemion, A., P. Komorowski, M. Surma, I. Ducin, P. Sobotka, M. Walczakowski, and E. Czerwińska. “Terahertz diffractive structures for compact in-reflection inspection setup.” Optics Express 28, no. 1 (2020): 715-723.
Two diffractive optical elements are used to create a compact raster THz scanning setup in reflective configuration. The first one focuses the radiation into the small focal spot on the sample, while the second one collects reflected radiation and focuses it on the detector. To assure small size of the setup and large apertures of optical elements, structures work in the off-axis geometry. Thus, the focal spot is formed 100 mm after and 60 mm below the optical axis of the element, which measures 75 mm in diameter. The designed iterative algorithm allows further minimization of these values.
…The refractive index for all frequencies in sub-THz range is equal to approximately 1.59 and the absorption coefficient corresponding to the frequency of 520 GHz is equal to 2.39 cm−1 . These measurements have been conducted using Teraview Spectra 3000 spectrometer for the sample of 3D printing material before manufacturing. Manufactured lenses measure 75 mm in diameter and up to 0.98 mm …