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.
Abstract
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.
for full paper see https://www.osapublishing.org/DirectPDFAccess/4CCAC4BA-E671-8D40-99D950830DE0A55F_425611/oe-28-1-715.pdf?da=1&id=425611&seq=0&mobile=no
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
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