Abstract-Opal-based terahertz optical elements fabricated by self-assembly of porous SiO2 nanoparticles

V. E. Ulitko, G. M. Katyba, V. A. Zhelnov, I. M. Shmytko, G. A. Emelchenko, I. E. Spector, V. M. Masalov, V. N. Kurlov, K. I. Zaytsev, M. Skorobogatiy, 

 Fabrication of the cylindrical convex-plane lenses by mechanical processing of bulk pieces of nanoporous SiO2${}_2$. (a) Multirun grinding of the lenses using rotational holder, and Removal of lenses from the holder after grinding. (b) 3D schematic of a cylindrical lens. (c) Photo of the fabricated lenses made of two nanoporous SiO2${}_2$ materials, annealed at the temperatures of 900$900$ and 1200∘${1200}^{\circ }$C and, thus, featuring different refractive indices and focal distances. (d) SEM images of the two nanoporous SiO2${}_2$ pieces made of 300$300$-nm-diameter nanoparticles and annealed at the temperatures of 900$900$ and 1200∘${1200}^{\circ }$C, respectively.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-29-9-13764&id=450313

In this paper, we study artificial opals as a promising material platform for terahertz (THz) optics. Materials were synthesized using self-assembly of porous SiO2 nanoparticles and annealing at different temperatures to further tune their optical properties. Two distinct approaches for the fabrication of bulk THz optics from these novel materials were considered. First, THz cylindrical lenses of identical geometry but different refractive indices and focal lengths were produced using standard mechanical processing of opals, in order to highlight their compatibility with conventional technologies of bulk optics fabrication. Second, a THz axicone was made via direct sedimentation of aqueous colloidal suspension of SiO2 nanoparticles in the mold of geometry inverse to that of a desired optical shape, followed by annealing and polishing. The second approach has an advantage of being considerably less labor intensive, while capable of obtaining optical elements of complex geometries. Thus fabricated bulk THz optical elements were studied experimentally using continuous-wave THz imaging, and the results were compared with 2D and 3D numerical predictions based on the finite-difference time-domain and finite-element frequency-domain methods. Our findings highlight technological robustness of the developed THz optical material platform and, thus, open the door for creating a variety of bulk THz optical elements of complex shapes and widely-tunable optical performance.

© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz dielectric spectroscopy of human brain gliomas and intact tissues ex vivo: double-Debye and double-overdamped-oscillator models of dielectric response

 

A. A. Gavdush, N. V. Chernomyrdin, G. A. Komandin, I. N. Dolganova, P. V. Nikitin, G. R. Musina, G. M. Katyba, A. S. Kucheryavenko, I. V. Reshetov, A. A. Potapov, V. V. Tuchin, K. I. Zaytsev,

 Ex vivo THz complex dielectric permittivity 𝜀̃$\tilde{\epsilon }$ of the intact tissues, edematous tissues and gliomas of the human brain: (a),(b) measured real 𝜀′${\epsilon }^{\prime }$ and imaginary 𝜀″${\epsilon }^{″}$ dielectric permittivity parts for the intact brain tissues, as compared with the DD (Eq. (3)) and DO (Eq. (4)) models; (c)–(l) the same data for the edematous tissues and gliomas; (m) the DD model parameters for water and tissues, from which parameters of the DO model can be calculated using Eq. (5). In (a)–(l), dielectric properties of tissues are compared with the DD model of liquid water from Ref. [42]. Here, GI$\text{I}$–GIV$\text{IV}$ stands for the WHO Grade I$\text{I}$–IV$\text{IV}$ gliomas.

https://www.osapublishing.org/boe/fulltext.cfm?uri=boe-12-1-69&id=444278

Terahertz (THz) technology offers novel opportunities in the intraoperative neurodiagnosis. Recently, the significant progress was achieved in the study of brain gliomas and intact tissues, highlighting a potential for THz technology in the intraoperative delineation of tumor margins. However, a lack of physical models describing the THz dielectric permittivity of healthy and pathological brain tissues restrains the further progress in this field. In the present work, the ex vivo THz dielectric response of human brain tissues was analyzed using relaxation models of complex dielectric permittivity. Dielectric response of tissues was parametrized by a pair of the Debye relaxators and a pair of the overdamped-oscillators – namely, the double-Debye (DD) and double-overdamped-oscillator (DO) models. Both models accurately reproduce the experimental curves for the intact tissues and the WHO Grades I–IV gliomas. While the DD model is more common for THz biophotonics, the DO model is more physically rigorous, since it satisfies the sum rule. In this way, the DO model and the sum rule were, then, applied to estimate the content of water in intact tissues and gliomas ex vivo. The observed results agreed well with the earlier-reported data, justifying water as a main endogenous label of brain tumors in the THz range. The developed models can be used to describe completely the THz-wave – human brain tissues interactions in the frameworks of classical electrodynamics, being quite important for further research and developments in THz neurodiagnosis of tumors.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-FDTD-modelling of terahertz solid immersion microscopy

V. A. Zhelnov,  N. V. Chernomyrdin, A. S. Kucheryavenko,  I. N. Dolganova,  G. M. Katyba,  K. I. Zaytsev,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11164/111640H/FDTD-modelling-of-terahertz-solid-immersion-microscopy/10.1117/12.2532389.short

Terahertz (THz) solid immersion microscopy is a novel THz imaging modality, which provides both a sub- wavelength spatial resolution and a high energy efficiency, thanks to the absence of sub-wavelength apertures and probes in an optical scheme. In this work, we apply the finite-difference time-domain technique for solving the Maxwell's equations in order to analyze the performance of our original THz SIL arrangement. Namely, we estimate the theoretical limits for the spatial resolution and the depth of field of our optical system, as well as specify the confidential intervals for the alignment of optical elements. The observed results demonstrate the resolution of 0:15λ and the depth of field of 0:12λ(λ is an electromagnetic wavelength), justifying advanced performance of our THz SIL.

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