Tuesday, 4 September 2018

Dynamic Photoinduced Controlling of the Large Phase Shift of Terahertz Waves via Vanadium Dioxide Coupling Nanostructures

Zhao, Yuncheng, Yaxin Zhang, Qiwu Shi, Shixiong Liang, Wanxia Huang, Wei Kou, and Ziqiang Yang. "Dynamic Photoinduced Controlling of the Large Phase Shift of Terahertz Waves via Vanadium Dioxide Coupling Nanostructures." ACS Photonics 5, no. 8 (2018): 3040-3050.

for full paper see https://pubs.acs.org/doi/abs/10.1021/acsphotonics.8b00276

… THz-TDS). The THz-TDS system is produced by Teraview company (Teraview TPS 3000). In this system, the Terahertz transmitter and detector are laser gated photo-conductive semiconductor devices. The femtosecond pulse … 


Abstract Image
Utilizing terahertz (THz) waves to transmit data for communication and imaging places high demands on phase modulation. However, until now, it is difficult to realize a more than 100° phase shift in the transmission mode with one-layer structure. In this paper, a ring-dumbbell composite resonator nested with VO2 nanostructures is proposed to achieve the large phase shift. It is found that in this structure a hybrid mode with an enhanced resonant intensity, which is coupled by the L-C resonance and dipole resonance has been observed. Applying the photoinduced phase transition characteristics of VO2, the resonant intensity of the mode can be dynamically controlled, which leads to a large phase shift in the incident THz wave. The dynamic experimental results show that controlling the power of the external laser can achieve a phase shift of up to 138° near 0.6 THz using this one-layer VO2 nested composite structure. Moreover, within a 55 GHz (575–630 GHz) bandwidth, the phase shift exceeds 130°. This attractive phase shift modulation may provide prospective applications in THz imaging, communications, and so on.

Monday, 3 September 2018

Assessment of Terahertz Imaging for Excised Breast Cancer Tumors with Image Morphing

Chavez, Tanny, Tyler Bowman, Jingxian Wu, Keith Bailey, and Magda El-Shenawee. "Assessment of Terahertz Imaging for Excised Breast Cancer Tumors with Image Morphing." Journal of Infrared, Millimeter, and Terahertz Waves (2018): 1-20.
This paper presents an image morphing algorithm for quantitative evaluation methodology of terahertz (THz) images of excised breast cancer tumors. Most current studies on the assessment of THz imaging rely on qualitative evaluation, and there is no established benchmark or procedure to quantify the THz imaging performance. The proposed morphing algorithm provides a tool to quantitatively align the THz image with the histopathology image. Freshly excised xenograft murine breast cancer tumors are imaged using the pulsed THz imaging and spectroscopy system in the reflection mode. Upon fixing the tumor tissue in formalin and embedding in paraffin, a formalin-fixed paraffin-embedded (FFPE) tissue block is produced. A thin slice of the block is prepared for the pathology image while another THz reflection image is produced directly from the block. We developed an algorithm of mesh morphing using homography mapping of the histopathology image to adjust the alignment, shape, and resolution to match the external contour of the tissue in the THz image. Unlike conventional image morphing algorithms that rely on internal features of the source and target images, only the external contour of the tissue is used to avoid bias. Unsupervised Bayesian learning algorithm is applied to THz images to classify the tissue regions of cancer, fat, and muscles present in xenograft breast tumors. The results demonstrate that the proposed mesh morphing algorithm can provide more effective and accurate evaluation of THz imaging compared with existing algorithms. The results also showed that while THz images of FFPE tissue are highly in agreement with pathology images, challenges remain in assessing THz imaging of fresh tissue.
Funding Information
This work was funded by the National Institutes of Health under Award No. R15CA208798. It was also funded in part by the National Science Foundation under Award Nos. 1408007 and 1711087.
… 2 Pulsed THz Imaging and Spectroscopy System The THz system is a TPS Spectra 3000 (#TeraView, Ltd.) pulsed terahertz imaging and spectroscopy system at the #University of Arkansas [5–8]. A diagram of the system is given in Fig …

Tuesday, 10 July 2018

Proton irradiation induced changes in glass and polyethylene terephthalate substrates for photovoltaic solar cells

Čermák, J., L. Mihai, D. Sporea, Y. Galagan, J. Fait, A. Artemenko, P. Štenclová, B. Rezek, M. Straticiuc, and I. Burducea. "Proton irradiation induced changes in glass and polyethylene terephthalate substrates for photovoltaic solar cells." Solar Energy Materials and Solar Cells 186 (2018): 284-290.
… The results are presented in the form of the ratio S irradiated non-irradiated . THz spectroscopy was performed by a TPS3000 spectrometer (TeraView) in the spectral range 0.06–2 THz using a spectral …
An alkaline earth boro-aluminosilicate glass (Eagle XG), a soda-lime glass, and a light-weight polyethylene-terephthalate (PET) foil, used as typical substrates for photovoltaics, were treated by an energetic proton beam (3 MeV, dose 106–107 Gy) corresponding to approx. 30 years of operation at low Earth orbit. Properties of the irradiated substrates were characterized by atomic force microscopyoptical absorption, optical diffuse reflectance, Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and terahertz (THz) spectroscopy. Minimal changes of optical and morphological properties are detected on the bare Eagle XG glass, whereas the bare PET foil exhibits pronounced increase in optical absorption, generation of photoluminescence, as well as mechanical bending. On the other hand, the identical substrates coated with Indium-tin-oxide(ITO), which is a typical material for transparent electrodes in photovoltaics, exhibit significantly higher resistance to the modifications by protons while ITO structural and electronic properties remain unchanged. The experimental results are discussed considering a potential application of these materials for missions in space.

for full paper https://www.sciencedirect.com/science/article/pii/S0927024818303568

Monday, 9 July 2018

Visualization of subsurface damage in woven carbon fiber-reinforced composites using polarization-sensitive terahertz imaging

Dong, Junliang, Pascal Pomarède, Lynda Chehami, Alexandre Locquet, Fodil Meraghni, Nico F. Declercq, and D. S. Citrin. "Visualization of subsurface damage in woven carbon fiber-reinforced composites using polarization-sensitive #terahertz imaging." NDT & E International (2018).

for full paper see https://www.sciencedirect.com/science/article/pii/S0963869518301610

Polarization-sensitive #terahertz imaging is applied to characterize subsurface damage in woven carbon fiber-reinforced composite laminates in this study. #Terahertz subsurface spectral imaging based on #terahertz deconvolution is tailored and applied to detect, in a nondestructive fashion, the subsurface damage within the first ply of the laminate caused by a four-point bending test. Subsurface damage types, including matrix cracking, fiber distortion/fracture, as well as intra-ply delamination, are successfully characterized. Our results show that, although the conductivity of carbon fibers rapidly attenuates terahertz propagation with depth, the imaging capability of #terahertz radiation on woven carbon fiber-reinforced composites can nonetheless be significantly enhanced by taking advantage of the #terahertz polarization and terahertz deconvolution. The method demonstrated in this study is capable of extracting and visualizing a number of fine details of the subsurface damage in woven carbon fiber-reinforced composites, and the results achieved are confirmed by comparative studies with X-ray tomography.

… thickness direction). The commercial THz time-domain spectroscopy (TDS) system (Teraview TPS Spectra 3000), which was employed in this study, is shown schematically.....

for more information about TeraView see https://www.azom.com/equipment-details.aspx?EquipID=4411

Experimental Gouy phase shift compensation in Terahertz time-domain spectroscopy

Koleják, Pierre, Kamil Postava, Martin Micica, Petr Kuzel, Filip Kadlec, and Jaromír Pištora. "Experimental Gouy phase shift compensation in Terahertz time-domain spectroscopy." Photonics and Nanostructures-Fundamentals and Applications(2018).

Terahertz time-domain spectroscopy experiments are usually carried out with focused beams. In this case the Gouy phase shift modifies the retrieved dielectric spectra of thick samples [Opt. Express 18, 15338 (2010)]. We show that a significant influence of the Gouy shift occurs also in commercial THz spectrometers where the focusing conditions may be a priori unknown. A method of experimental compensation of the Gouy shift influence is described and demonstrated.

… In this work we use the time domain spectrometer TeraviewTPS Spectra 3000, which uses 90 fs pulses at 780 nm delivered by the second harmonic of Er:doped fiber laser …Scheme of the measuring system (TPS spectra 3000 from Teraview company) with the … 

For more information about TeraView see https://www.azom.com/equipment-details.aspx?EquipID=4411

for full paper see https://www.sciencedirect.com/science/article/pii/S1569441017303048