Abstract-Flexible materials for terahertz optics: advantages of graphite-based structures

Rusnė Ivaškevičiūtė-Povilauskienė, Linas Minkevičius, Domas Jokubauskis, Andrzej Urbanowicz, Simonas Indrišiūnas, and Gintaras Valušis

 THz-TDS transmittance spectra and insets depict THz-CW two-dimensional THz beam profiles focused with a) metal TZP; b) graphite foil TZP; c) graphite on paper TZP; d) pure paper TZP. The beam cross sections at the maximum intensity are presented in a linear scale as a solid black line for each case. Maximum signal amplitude of the TZPs is normalized to the maximum amplitude of the unfocused beam.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-9-11-4438

Flexible materials for applications in terahertz (THz) range imaging systems are investigated in this study. THz time-domain spectroscopy and THz imaging at 0.6 THz frequency are used to analyze optical properties of zone plates (TZP) with integrated cross-shaped filters, which are fabricated using direct laser writing on thin graphite, HB pencil-shaded graphite on paper, as well as reference metal-based and pure paper zone plates. Spectral features and focusing power comparable to the best metal-based TZP is achieved with graphite-based TZP. The pure paper and paper with pencil-shaded graphite TZPs showed increase in focusing power by a factor of ∼1.5, supporting numerical 3D finite-difference time-domain simulations. The findings show that graphite-based TZPs can serve as a flexible, compact, and inexpensive optics elements for emerging THz imaging systems.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Focusing of Terahertz Radiation With Laser-Ablated Antireflective Structures

 Milda Tamošiūnaitė,  Simonas Indrišiūnas, Vincas Tamošiūnas,   Linas Minkevičius,  Andrzej Urbanowicz,  Gediminas Račiukaitis,   Irmantas Kašalynas,  Gintaras Valuši

https://ieeexplore.ieee.org/document/8419328/

Numerical simulations and experimental characterization of laser-ablated focusing antireflective and phase-shifting structures for terahertz frequencies are presented. More than 10% shift of reflectance minimum to lower frequencies was predicted by simulations for relatively coarse structures with the period of 100  μ m in comparison with that of a substantially smaller period and with results of the model used for the design of antireflective surfaces in the terahertz range. Such a shift of the resonance frequency can be employed to optimize the thickness of antireflective layers simultaneously obtaining additional means of more precise control of layer properties due to ablation of larger structures. Nearly 90% transmittance of silicon wafers within 0.5–0.6 THz frequencies was confirmed experimentally. Optical path differences equivalent to a half period at 0.53 THz, suitable for applications in high-efficiency zone plates, were demonstrated with high transmittance simultaneously. Possibilities of delay adjustment up to one wavelength were illustrated by numerical simulations. A focusing binary zone plate for 0.6 THz was produced employing phase-shift differences of the dual-function antireflective layer. Its close to diffraction-limited focusing performance was evaluated, further confirming sufficient uniformity of the structured layer.