Terahertz Time-of-Flight Tomography Beyond the Axial Resolution Limit: Autoregressive Spectral Estimation Based on the Modified Covariance Method

Zhai, Min, Alexandre Locquet, Cyrielle Roquelet, and D. S. Citrin. "Terahertz Time-of-Flight Tomography Beyond the Axial Resolution Limit: Autoregressive Spectral Estimation Based on the Modified Covariance Method." Journal of Infrared, Millimeter, and Terahertz Waves (2020): 1-14.

Abstract

We present a time-of-flight tomography method for exceeding the naïve axial (i.e., depth) resolution limit of terahertz (THz) deconvolution by autoregressive spectral extrapolation (AR) based on the modified covariance method (AR/MCM). In contrast to Wiener filtering combined with wavelet denoising, AR/MCM does not discard any frequency components in the low signal-to-noise (SNR) regions of the measured data, and unlike the AR approach based on the Burg method (AR/BM), no peak splitting (single peaks in the impulse response function appearing as double peaks) as well as frequency bias (spectral peaks shifted with respect to their correct positions) is observed after deconvolution. After verifying the advantages of AR/MCM over Wiener filtering in conjunction with wavelet denoising as well as over AR/BM, using synthetic data, AR/MCM is employed to reconstruct a single layer of mill scale on a steel coupon from experimental THz time-of-flight tomography data. The reconstruction shows good agreement with the film thickness obtained from destructive cross-sectional measurements. In addition, unlike AR/BM, optimizing the parameters to obtain stable reconstruction is straightforward relying of Akaike’s information criterion suggesting that AR/MCM can be an easier to implement for THz nondestructive characterization of stratigraphy under noisy conditions, particularly when estimates of the stratigraphy may not a priori be available.

Full paper can be found at https://link.springer.com/article/10.1007/s10762-020-00722-1

… that minimizes the AIC. Experiment. The measurement in this work is carried out using a pulsed, broadband THz time domain system from TeraView Ltd. (TPSSpectra 3000), shown schematically in Fig. 1. The GaAs photoconductive …

High performance of talented copper/magneso-zinc titanate nanostructures as biocidal agents for inactivation of pathogens during wastewater disinfection

Nahrawy, Amany M. El, Ahmed M. Bakr, Ali B. Abou Hammad, and Bahaa A. Hemdan. "High performance of talented copper/magneso-zinc titanate nanostructures as biocidal agents for inactivation of pathogens during wastewater disinfection." Applied Nanoscience: 1-17.

Abstract

In the present research, the performance of MZT nano-titanate was established by combining (0.3–0.5) copper nanoparticles (0–0.5C-MZT) to improve the antimicrobial efficacy of promising engineered nanomaterials. XRD characterized the phase purity confirms the formation of magneto-zinc and copper titanates at 750 °C. The morphological features of four engineering nanoceramics were accurately described. As well, the inactivation effects of microbial growth were also evaluated for these kinds of engineered nanomaterials. After that, the disinfection of estimating four harmful waterborne bacteria in real wastewater was appraised. The results obtained of Raman active modes and FT-IR exhibit that the crystallization was strengthened by Cu doping. The natural THz response of the samples appears a distinct attenuation in the THz transmission. In addition, the results showed that 0.5C-MZT is a powerful antimicrobial agent for damaging the targeted pathogens. The results of toxicological safety tests indicated that the nanomaterials examined are safe for environmental applications. The results achieved reveal that the examined proficient dosage (200 mg/L) of studied 0.5C-MZT nanomaterials was practiced to deactivate four predominant waterborne pathogens in wastewater. Eventually, MZT could serve as a smart nano-weapon towards numerous sorts of dangerous pathogenic microbes and results; therefore, recommend that MZT can be employed as a talented disinfecting agent within wastewater processing.

for full paper see https://link.springer.com/article/10.1007%2Fs13204-020-01454-3

… Standard transmission THz/TDS coordination is occupied for measurements using the TPS spectra 3000 system (Teraview Ltd. England) model by using the transmission unit of polyethylene pelts and under Nitrogen gas (N2) purging …

Utilizing multilayer structures to enhance terahertz characterization of thin films ranging from aqueous solutions to histology slides

Sun, Qiushuo, Kai Liu, Xuequan Chen, Xudong Liu, A. I. Hernandez-Serrano, and Emma Pickwell-MacPherson. "Utilizing multilayer structures to enhance terahertz characterization of thin films ranging from aqueous solutions to histology slides." Optics letters 44, no. 9 (2019): 2149-2152.

Abstract

We propose a multilayer geometry to characterize thin-film samples in reflection terahertz time domain spectroscopy. Theory indicates that this geometry has higher sensitivity compared to ordinary transmission or reflection geometries when characterizing both low- and high-absorption samples. Pure water and water–ethanol mixtures are measured to verify the characterization accuracy of the proposed geometry and its capability to measure trace liquids. Paraffin-embedded oral cancer tissue is imaged to further show how the proposed geometry enhances the sensitivity for solid low-absorptive films.

for full paper see https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-9-2149

"The TF liquid measurements were conducted using the Terapulse 4000 from Teraview Ltd. The ethanol (≥99.8%) was from SIGMA-ALDRICH CO. The dove prism was made of fused quartz with a top angle of 38°. The top medium in the liquid measurements was a 2mm-thick fused quartz substrate. 25 µm Teflon spacers were sandwiched in the middle between the quartz prism and the substrate. The incident wave was p-polarized"

2020 OSA Awards and Medals

The OSA has awarded the William F. Meggers Award for recognition of his outstanding work in spectroscopy to Tony F. Heinz

Stanford University and SLAC National Accelerator Laboratory, USA 

For seminal studies of the properties and dynamics of surfaces, interfaces, and nanoscale materials by diverse spectroscopic techniques, including through the development of powerful new methods .

Tony Heinz received a B.S. in physics from Stanford University, USA, and a Ph.D. in physics from the University of California, Berkeley, USA. He is a professor of applied physics and photon science at Stanford University and the Associate Laboratory Director for Energy Sciences at SLAC National Accelerator Laboratory. Previously, he was a research staff member at the IBM Watson Research Center, USA, and a professor of physics and electrical engineering at Columbia University, USA. He is a Fellow of OSA and served as OSA President in 2012. Heinz has developed a wide range of spectroscopic techniques to examine the properties and dynamics of nanoscale systems. These methods include interface sensitive nonlinear spectroscopy and time-resolved approaches, such as terahertz time-domain techniques. The measurement techniques have been applied to elucidate the electronic, optical and chemical properties of 0-, 1-, and 2-dimensional materials and interfaces.  The research  would not have been possible without the insight and hard work of more than 70 graduate students and postdocs over the years.

Influence of SiO2 nanoparticles on morphology, optical, and conductivity properties of Poly (ethylene oxide)

Hameed, Talaat A., F. Mohamed, A. M. Abdelghany, and G. Turky. "Influence of SiO."

Abstract

In this work, a detailed insight to the microstructure, morphology, surface topography, electrical and optical properties in visible and terahertz range was presented for polyethylene oxide (PEO)/silicon dioxide SiO2 nanocomposites. PEO-filled with various contents of SiO2 nanoparticles were synthesized via the solution cast technique. The polycrystalline nature of PEO/SiO2 films was affirmed by the selected area electron diffraction pattern (SAED) recorded by HRTEM measurement and it was found to nearly conformable with X-ray diffraction data. The energy-dispersive X-ray analysis (EDAX) proved the existence of SiO2 with wt% ranged from 0 to 5% as starting fillers. The high-resolution scanning electron microscope planar images indicated uniform distribution of SiO2 nanoparticles within the PEO films. The atomic force microscope 3D images depicted the surface changed from rough to smooth upon the filling with SiO2. The composite samples exhibit absorption spectra that extended from UV–Vis to near infrared regions. Based on Tauc's formula, it was found that the absorption edge shifted from 4.90 to 3.20 eV as the filler fraction increased from 0 to 5 wt%. The analysis of reflective index in the UV–Vis–NIR regions displayed decrement with increasing filler content. Moreover, the refractive index in Vis–NIR regions is good extension to that in THz region expressing the optical quality of studied films. The optical dispersion parameters were analyzed in the view of Wemple-Didomenico single oscillator and Sellmeier model. The values of nonlinear optical parameters (nonlinear susceptibility χ(3) and nonlinear refractive index (n2) were influenced by the filler fractions. Upon the rise of filler content, the conductivity values show slightly decrement.

for full paper see https://link.springer.com/article/10.1007%2Fs10854-020-03591-5