Репозиторий Университета

© 2018 IEEE. We have proposed an approach to improve the resolution of terahertz (THz) imaging using the effect of solid immersion - i.e. a reduction in the dimensions of the electromagnetic beam caustic by its formation in a free space, behind the medium possessing high refractive index. We have designed a THz solid immersion lens (SIL) comprised of a polymer wide-aperture aspherical singlet and a crystalline truncated sphere mounted in front of the image plane. We have proposed an approach for the object handling at the focal plane of the THz SIL. We have combined numerical simulations and experimental studies to demonstrate the advanced 0.2λ spatial resolution of the proposed THz SIL - it is beyond the 0.5λ Abbe limit. Finally, we have assembled the continuous-wave THz SIL imaging system and applied it for studying various objects with sub-wavelength variations of structure and dielectric properties.

© 2018 IEEE. We have proposed a method of THz solid immersion microscopy, which yields imaging soft biological tissues with the sub-wavelength resolution up to 0.2-wavelengths. To achieve this advanced resolution, it employs a solid immersion phenomenon - i.e. a reduction in the dimensions of the THz beam caustic by its formation on a small distance behind the medium featuring high refractive index. We have assembled an experimental setup, which realizes the principles of the THz solid immersion microscopy, and proposed an approach for handling the soft tissue at the object plane. This setup uses a backward-wave oscillator, as a source of continuous-wave THz radiation, and a Golay cell, as a detector of the THz field intensity. We have examined the resolution of the THz solid immersion microscopy using both numerical simulations and experimental studies. Finally, in order to highlight the prospective of the proposed THz imaging modality, we have applied the experimental setup for imaging of representative examples of biological tissues.

© 2018 IEEE. Modern progress in terahertz (THz) diagnostics of malignancies, including non-invasive, least-invasive and intraoperative techniques is briefly discussed. Special attention is paid to intraoperative diagnosis of brain tumors, which is a rapidly developing field nowadays. We discuss our recent results in this research field, which are associated with (i) in vitro studies the THz dielectric response of gelatin-embedded human brain tumors (including gliomas and meningiomas featuring different grades), (ii) analysis an ability for differentiation between normal and pathological tissues of the brain relying on the methods of THz spectroscopy and imaging, and, finally, (iii) development of novel THz instrumentation for the intraoperative detection of margins of tumors in order to guarantee its gross total resection.

© 2018 IEEE. In this paper, we propose a computational approach for description of radiation transfer in a quasi-ordered medium and study the impact of scattering on electromagnetic wave propagation and image formation. It combines finite-difference time-domain method, Monte Carlo simulations, and radiative transfer theory. Using, as an example, terahertz (THz) imaging, we analyze the modulation transfer function (MTF) of the imaging system operated at 0.25 THz for scattering material layers placed between the object and the imaging plane. We experimentally study imaging of bar-pattern test objects through a quasi-ordered scattering medium. Both numerical and experimental results are in good agreement and demonstrate an impact of quasi-ordered scatterers on quality of THz images, i.e., particular combination of the electromagnetic wavelength and parameters of scattering materials could enhance MTF compared with ones with random particle structures.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. We have developed a method of the terahertz (THz) solid immersion microscopy for the reflection-mode imaging of soft biological tissues. It relies on the use of the solid immersion lens (SIL), which employs the electromagnetic wave focusing into the evanescent-field volume (i.e. at a small distance behind the medium possessing high refractive index) and yields reduction in the dimensions of the THz beam caustic. We have assembled an experimental setup using a backward-wave oscillator, as a source of the continuous-wave THz radiation featuring λ= 500 μm, a Golay cell, as a detector of the THz wave intensity, and a THz SIL comprised of a wide-aperture aspherical singlet, a truncated sphere and a thin scanning windows. The truncated sphere and the scanning window are made of high-resistivity float-zone silicon and form a unitary optical element mounted in front of the object plane for the resolution enhancement. The truncated sphere is rigidly fixed, while the scanning window moves in lateral directions, allowing for handling and visualizing the soft tissues. We have applied the experimental setup for imaging of a razor blade to demonstrate the advanced 0:2λ resolution of the proposed imaging arrangement. Finally, we have performed imaging of sub-wavelength-scale tissue spheroids to highlight potential of the THz solid immersion microscopy in biology and medicine.