Extracting Complex Dielectric Properties From Reflection-Transmission Mode Spectroscopy

Sun, Jingye, and Stepan Lucyszyn. "Extracting Complex Dielectric Properties From Reflection-Transmission Mode Spectroscopy." IEEE Access 6 (2018): 8302-8321.

Abstract:

Material characterization of homogeneous dielectric slabs using reflection–transmission mode spectroscopy can be problematic due to the ambiguity from a phasor term. A comprehensive analytical review of methods for calculating the normalized power spectra, to extract the effective complex dielectric properties of a sample, is undertaken. Three generic power response models (zero-order, power propagation, and electric-field propagation) are derived; these models act as a consolidated mathematical framework for the whole paper. With our unified engineering approach, the voltage-wave propagation, transmission line, and telegrapher’s equation transmission line models are then independently derived; the first two giving the same mathematical solutions, whereas the third generates the same numerical results, as the exact electric-field propagation model. Mathematically traceable simulation results from the various models are compared and contrasted using an arbitrarily chosen data set (window glass) from 1 to 100 THz. We show how to extract the approximate effective complex dielectric properties using time-gated time-domain spectroscopy and also the exact values with our theoretical graphical techniques from the first-order reflectance and transmittance. Our approach is then taken further by considering all the Fabry–Pérot reflections with the frequency- and space-domain spectroscopy. With the scalar reflection–transmission mode infrared spectroscopy, we model the threshold conditions between the solution space that gives the single (exact) solution for the complex refractive index and the solution space that gives multiple mathematical solutions. By knowing threshold conditions, it is possible to gain a much deeper insight, in terms of the sample constraints and metrology techniques that can be adopted, to determine the single solution. Finally, we propose a simple additional measurement/simulation step to resolve the ambiguity within the multiple solution space. Here, sample thickness is arbitrary and no initial guesses are required. In theory, the result from this paper allows for the exact extraction of complex dielectric properties using simpler and lower cost scalar reflection–transmission mode spectroscopy.

for full paper see http://ieeexplore.ieee.org/abstract/document/8268097/

Concentration analysis of breast tissue phantoms with terahertz spectroscopy

Truong, Bao CQ, Anthony J. Fitzgerald, Shuting Fan, and Vincent P. Wallace. "Concentration analysis of breast tissue phantoms with terahertz spectroscopy." Biomedical optics express 9, no. 3 (2018): 1334-1349.

Abstract

Terahertz imaging has been previously shown to be capable of distinguishing normal breast tissue from its cancerous form, indicating its applicability to breast conserving surgery. The heterogeneous composition of breast tissue is among the main challenges to progressing this potential research towards a practical application. In this paper, two concentration analysis methods are proposed for analyzing phantoms mimicking breast tissue. The dielectric properties and the double Debye parameters were used to determine the phantom composition. The first method is wholly based on the conventional effective medium theory while the second one combines this theoretical model with empirical polynomial models. Through assessing the accuracy of these methods, their potential for application to quantifying breast tissue pathology was confirmed.

for full paper see https://www.osapublishing.org/DirectPDFAccess/05AFAAF3-AAC5-9BF4-273918F849D54E5A_382131/boe-9-3-1334.pdf?da=1&id=382131&seq=0&mobile=no

More information: TeraView 

Extraordinary THz transmission with a small beam spot: the leaky wave mechanism

Navarro‐Cía, Miguel, Víctor Pacheco‐Peña, Sergei A. Kuznetsov, and Miguel Beruete. "Extraordinary THz Transmission with a Small Beam Spot: The Leaky Wave Mechanism." Advanced Optical Materials (2018).

Abstract

The discovery of extraordinary optical transmission (EOT) through patterned metallic foils in the late 1990s was decisive for the development of plasmonics and cleared the path to employ small apertures for a variety of interesting applications all along the electromagnetic spectrum. However, a typical drawback often found in practical EOT structures is the large size needed to obtain high transmittance peaks. Consequently, practical EOT arrays are usually illuminated using an expanded (mimicking a plane wave) beam. Here, it is shown with numerical and experimental results in the THz range that high transmittance peaks can be obtained even with a reduced illumination spot exciting a small number of holes, provided that the structure has a sufficient number of lateral holes out of the illumination spot. These results shed more light on the prominent role of leaky waves in the underlying physics of EOT and have a direct impact on potential applications.

for full paper see https://onlinelibrary.wiley.com/doi/full/10.1002/adom.201701312

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Quantum Electric Dipole Lattice

Dressel, Martin, Elena S. Zhukova, Victor G. Thomas, and Boris P. Gorshunov. "Quantum Electric Dipole Lattice." Journal of Infrared, Millimeter, and Terahertz Waves (2018): 1-17.

Abstract

Water is subject to intense investigations due to its importance in biological matter but keeps many of its secrets. Here, we unveil an even other aspect by confining H2O molecules to nanosize cages. Our THz and infrared spectra of water in the gemstone beryl evidence quantum tunneling of H2O molecules in the crystal lattice. The water molecules are spread out when confined in a nanocage. In combination with low-frequency dielectric measurements, we were also able to show that dipolar coupling among the H2O molecules leads towards a ferroelectric state at low temperatures. Upon cooling, a ferroelectric soft mode shifts through the THz range. Only quantum fluctuations prevent perfect macroscopic order to be fully achieved. Beside the significance to life science and possible application, nanoconfined water may become the prime example of a quantum electric dipolar lattice.

"Complementary experiments were conducted utilizing a pulsed THz time-domain TeraView spectrometer. "

for full paper see https://link.springer.com/article/10.1007/s10762-018-0472-8

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Pulsed terahertz imaging of breast cancer in freshly excised murine tumors

Bowman, Tyler, Tanny Chavez, Kamrul Khan, Jingxian Wu, Avishek Chakraborty, Narasimhan Rajaram, Keith Bailey, and Magda El-Shenawee. "Pulsed terahertz imaging of breast cancer in freshly excised murine tumors." Journal of Biomedical Optics 23, no. 2 (2018): 026004.

Abstract

This paper investigates terahertz (THz) imaging and classification of freshly excised murine xenograft breast cancer tumors. These tumors are grown via injection of E0771 breast adenocarcinoma cells into the flank of mice maintained on high-fat diet. Within 1 h of excision, the tumor and adjacent tissues are imaged using a pulsed THz system in the reflection mode. The THz images are classified using a statistical Bayesian mixture model with unsupervised and supervised approaches. Correlation with digitized pathology images is conducted using classification images assigned by a modal class decision rule. The corresponding receiver operating characteristic curves are obtained based on the classification results. A total of 13 tumor samples obtained from 9 tumors are investigated. The results show good correlation of THz images with pathology results in all samples of cancer and fat tissues. For tumor samples of cancer, fat, and muscle tissues, THz images show reasonable correlation with pathology where the primary challenge lies in the overlapping dielectric properties of cancer and muscle tissues. The use of a supervised regression approach shows improvement in the classification images although not consistently in all tissue regions. Advancing THz imaging of breast tumors from mice and the development of accurate statistical models will ultimately progress the technique for the assessment of human breast tumor margins

"This work makes use of the TPS Spectra 3000 THz pulsed imaging and spectroscopy system (TeraView, Ltd., United Kingdom) at the University of Arkansas."


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For full paper see https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-23/issue-2/026004/Pulsed-terahertz-imaging-of-breast-cancer-in-freshly-excised-murine/10.1117/1.JBO.23.2.026004.short?SSO=1