Репозиторий Университета

© 2018 IEEE. We study both theoretically and experimentally an ability for shaping the spectra of the terahertz (THz) pulses, emitted by a photoconductive antennas (PCAs) with the logspiral configuration of electrodes, by impedance matching. We select and fabricate 2 configurations of the LT-GaAs PCAs possessing different frequency-dependent impedances and THz spectra. By comparing the results of our studies, we firstly demonstrate high-to-moderate correlation between the frequency-dependent impedance matching efficiency and the THz spectra. The proposed approach makes possible optimizing the PCA performance for accommodating the needs of the THz technology use in various branches, especially in condensed matter and biomedicine.

© 2018 IEEE. In our work, we have performed in vitro terahertz (THz) measurements of gelatin-embedded malignant human brain gliomas using the THz pulsed spectroscopy. The gelatin embedding yields sustain the THz response of tissues close to that of the freshly-excised ones for a long time after the resection. We have observed significant differences between the THz responses of normal and pathological tissues of the brain, which highlights a potential of the THz technology in label-free intraoperative neurodiagnosis of tumors.

© 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 SPIE.  We have investigated the influence of indium content (x) increase on spectral characteristics of In x Ga 1-x As photoconductor. To avoid the mismatch between crystalline parameters of In x Ga 1-x As and GaAs wafer we proposed to incorporate a step-graded metamorphic buffer layer. We showed that x increase strongly enhances THz emission and broadens THz spectrum of In x Ga 1-x As. Since no polarity rehearsal of the THz waveform occurs and electron diffusion mobility increases up to 90% with x increase we attribute the increase of THz intensity to photo-Dember effect contribution. The maximum efficiency of optical-to-THz conversion was obtained for In 0.72 Ga 0.28 As at optical fluence ∼0.01 μJ=cm 2 . The fabricated photoconductors can be used as promising photo-Dember or lateral photo-Dember THz emitters in pulsed THz spectroscopy and imaging, in particular, operating with long wave optical pump.

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. We have performed the in vitro terahertz (THz) spectroscopy of human brain tumors. In order to fix tissues for the THz measurements, we have applied the gelatin embedding. It allows for preserving tissues from hydration/dehydration and sustaining their THz response similar to that of the freshly-excised tissues for a long time after resection. We have assembled an experimental setup for the reflection-mode measurements of human brain tissues based on the THz pulsed spectrometer. We have used this setup to study in vitro the refractive index and the amplitude absorption coefficient of 2 samples of malignant glioma (grade IV), 1 sample of meningioma (grade I), and samples of intact tissues. We have observed significant differences between the THz responses of normal and pathological tissues of the brain. The results of this paper highlight the potential of the THz technology in the intraoperative neurodiagnosis of tumors relying on the endogenous labels of tumorous tissues.