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

Monitoring the role of enantiomers in the surface modification and adsorption process of polymers imprinted by chiral molecules: theory and practice

Woźnica, Marcin, Monika Sobiech, Norbert Pałka, and Piotr Luliński. "Monitoring the role of enantiomers in the surface modification and adsorption process of polymers imprinted by chiral molecules: theory and practice." Journal of Materials Science: 1-17.

ABSTRACT 

The objective of this study was to explore the role of enantiomers in the surface modification and adsorption process of polymers imprinted by chiral molecules. Here, R-, S- and R/S-1-aminoindanes (TR, TS and TR/S) were used as the model template molecules. Optimization of synthetic protocols facilitated preselection of the most efficient composition for a molecularly imprinted polymer (MIP)— methacrylic acid-co-ethylene glycol dimethacrylate—with satisfactory specificity and an imprinting factor equal to 3. This polymer composition was used further to analyse the effect of configuration of the template on adsorption properties. The results showed preferable adsorption of R-enantiomer, TR in the R-MIP and S-enantiomer, TS in the S-MIP but revealed variations in the binding capacities of TR and TS in the R- and S-cavity (stereoselectivity factor; k = 1.66 to 1.22, respectively). The theoretically analysed binding energies (DEB) of both TR and TS in the R-cavity (DEB = - 506.14 to - 256.77 kcal mol-1 ) and S-cavity (DEB = - 302.42 to - 347.18 kcal mol-1 ) were in agreement with empirical data. Morphology and porosity analyses revealed the impact of the template molecule on the pore system of the MIP and control (a non-imprinted polymer), but enantiomers were only found to have a negligible role. Binding characterization revealed that the physisorption-governed adsorption process and Dubinin– Radushkevich model fitted the experimental data best. Finally, terahertz spectroscopy was employed to confirm the similarity between both materials imprinted by each enantiomer.

for full paper see https://link.springer.com/content/pdf/10.1007/s10853-020-04796-z.pdf

… Terahertz spectroscopy was performed at the Military University of Technology Institute

of Opto- electronics, Warsaw, Poland. A TDS-based spec- trometer was used for terahertz

measurements (Teraview TPS Spectra 300, Cambridge, UK) in transmission …

Simultaneous Investigation of the Liquid Transport and Swelling Performance during Tablet Disintegration

Al-Sharabi, Mohammed, Daniel Markl, Theona Mudley, Prince Bawuah, Anssi-Pekka Karttunen, Cathy Ridgway, Patrick Gane et al. "Simultaneous Investigation of the Liquid Transport and Swelling Performance during Tablet Disintegration." International Journal of Pharmaceutics (2020): 119380.

Abstract

Fast disintegrating tablets have commonly been used for fast oral drug delivery to patients with swallowing difficulties. The different characteristics of the pore structure of such formulations influence the liquid transport through the tablet and hence affect the disintegration time and the release of the drug in the body. In this work, terahertz time-domain spectroscopy and terahertz pulsed imaging were used as promising analytical techniques to quantitatively analyse the impact of the structural properties on the liquid uptake and swelling rates upon contact with the dissolution medium. Both the impact of porosity and formulation were investigated for theophylline and paracetamol based tablets. The drug substances were either formulated with functionalised calcium carbonate (FCC) with porosities of 45% and 60% or with microcrystalline cellulose (MCC) with porosities of 10% and 25%. The terahertz results reveal that the rate of liquid uptake is clearly influenced by the porosity of the tablets with a faster liquid transport observed for tablets with higher porosity, indicating that the samples exhibit structural similarity in respect to pore connectivity and pore size distribution characteristics in respect to permeability. The swelling of the FCC based tablets is fully controlled by the amount of disintegrant, whereas the liquid uptake is driven by the FCC material and the interparticle pores created during compaction. The MCC based formulations are more complex as the MCC significantly contributes to the overall tablet swelling. An increase in swelling with increasing porosity is observed in these tablets, which indicates that such formulations are performance-limited by their ability to take up liquid. Investigating the effect of the microstructure characteristics on the liquid transport and swelling kinetics is of great importance for reaching the next level of understanding of the drug delivery, and, depending on the surface nature of the pore carrier function, in turn controlling the performance of the drug mainly in respect to dissolution in the body.

for full paper see https://www.sciencedirect.com/science/article/pii/S0378517320303641

"2.3. Terahertz Time-Domain Spectroscopy and Imaging. A commercial terahertz system (TeraPulse 4000, Teraview Ltd., Cambridge, UK) was used to conduct all the terahertz measurements in either transmission or reflection mode."

Terahertz-infrared electrodynamics of swingle-crystalline Ba0. 2Pb0. 8Al1. 2Fe10. 8O19 M-type hexaferrite

Ahmed, Asmaa, Anatoly S. Prokhorov, Vladimir Anzin, Denis Vinnik, Alexander Bush, Boris Gorshunov, and Liudmila Alyabyeva. "Terahertz-infrared electrodynamics of swingle-crystalline Ba0. 2Pb0. 8Al1. 2Fe10. 8O19 M-type hexaferrite." Journal of Alloys and Compounds (2020): 155462.

Abstract

Spectral response of single-crystalline Ba0.2Pb0.8Al1.2Fe10.8O19 synthesized by a modified Czochralski method is investigated using terahertz-infrared spectroscopy. Reflectivity, transmissivity, and complex dielectric permittivity spectra of the compound are studied in the temperature range from 6 to 300 K and in the frequency interval 8-8000 cm−1 for two principle polarizations of the radiation electric field relative to the crystallographic c-axis, namely E||c and E⊥c. The resonance absorption lines observed above 80 cm−1 are assigned to polar lattice vibrations basing on a factor group analysis and a comparison with a dielectric response of isostructural compounds. A set of absorption bands is observed in a range of 8–80 cm−1. To clarify their nature, a model is developed that considers electronic transitions within the fine-structured ground state of four-fold coordinated Fe2+. It is shown that the trigonal distortions of the crystal field lead to lowering of the symmetry of 4f1 and 4e tetrahedral site-positions of Fe2+ and, as a result, to further splitting of the ground state spin-orbital sub-levels. Electro-dipole transitions between the corresponding sub-levels are associated with the absorption lines observed in a low-energy response (at 8-80 cm−1) of the Ba0.2Pb0.8Al1.2Fe10.8O19 compound. The study paves the way for the development of low cost materials with high dielectric permittivity (about 30) at terahertz frequencies that are promising for the manufacture of electronic devices with enhanced characteristics.

for full see https://www.sciencedirect.com/science/article/abs/pii/S0925838820318260

Sub-lattice of Jahn-Teller centers in hexaferrite crystal

Gudkov, V. V., M. N. Sarychev, S. Zherlitsyn, I. V. Zhevstovskikh, N. S. Averkiev, D. A. Vinnik, S. A. Gudkova et al. "Sub-lattice of Jahn-Teller centers in hexaferrite crystal." Scientific Reports 10, no. 1 (2020): 1-15.

Abstract

A novel type of sub-lattice of the Jahn-Teller (JT) centers was arranged in Ti-doped barium hexaferrite BaFe₁₂O₁₉. In the un-doped crystal all iron ions, sitting in five different crystallographic positions, are Fe³⁺ in the high-spin configuration (S = 5/2) and have a non-degenerate ground state. We show that the electron-donor Ti substitution converts the ions to Fe²⁺ predominantly in tetrahedral coordination, resulting in doubly-degenerate states subject to the E⊗eE⊗e problem of the JT effect. The arranged JT complexes, Fe²⁺O₄, their adiabatic potential energy, non-linear and quantum dynamics, have been studied by means of ultrasound and terahertz-infrared spectroscopies. The JT complexes are sensitive to external stress and applied magnetic field. For that reason, the properties of the doped crystal can be controlled by the amount and state of the JT complexes.

for full paper see https://www.nature.com/articles/s41598-020-63915-7

They used a terahertz time-domain spectrometer (Teraview TPS 3000 TDS)

Terahertz-Based Porosity Measurement of Pharmaceutical Tablets: a Tutorial

Bawuah, Prince, Daniel Markl, Daniel Farrell, Mike Evans, Alessia Portieri, Andrew Anderson, Daniel Goodwin, Ralph Lucas, and J. Axel Zeitler. "Terahertz-based porosity measurement of pharmaceutical tablets: a tutorial." Journal of Infrared, Millimeter, and Terahertz Waves (2020): 1-20.

Abstract

Porosity, one of the important quality attributes of pharmaceutical tablets, directly affects the mechanical properties, the mass transport and hence tablet disintegration, dissolution and ultimately the bioavailability of an orally administered drug. The ability to accurately and quickly monitor the porosity of tablets during manufacture or during the manufacturing process will enable a greater assurance of product quality. This tutorial systematically outlines the steps involved in the terahertz-based measurement method that can be used to quantify the porosity of a tablet within seconds in a non-destructive and non-invasive manner. The terahertz-based porosity measurement can be performed using one of the three main methods, which are (i) the zero-porosity approximation (ZPA); (ii) the traditional Bruggeman effective medium approximation (TB-EMA); and (iii) the anisotropic Bruggeman effective medium approximation (AB-EMA). By using a set of batches of flat-faced and biconvex tablets as a case study, the three main methods are compared and contrasted. Overall, frequency-domain signal processing coupled with the AB-EMA method was found to be most suitable approach in terms of accuracy and robustness when predicting the porosity of tablets over a range of complexities and geometries. This tutorial aims to concisely outline all the necessary steps, precautions and unique advantages associated with the terahertz-based porosity measurement method.

for full paper see https://link.springer.com/article/10.1007/s10762-019-00659-0

Review of Terahertz Pulsed Imaging for Pharmaceutical Film Coating Analysis

Alves-Lima, Décio, Jun Song, Xiaoran Li, Alessia Portieri, Yaochun Shen, J. Axel Zeitler, and Hungyen Lin. "Review of Terahertz Pulsed Imaging for Pharmaceutical Film Coating Analysis." Sensors 20, no. 5 (2020): 1441.

Terahertz pulsed imaging (TPI) was introduced approximately fifteen years ago and has attracted a lot of interest in the pharmaceutical industry as a fast, non-destructive modality for quantifying film coatings on pharmaceutical dosage forms. In this topical review, we look back at the use of TPI for analysing pharmaceutical film coatings, highlighting the main contributions made and outlining the key challenges ahead.

for full paper see https://www.mdpi.com/1424-8220/20/5/1441

Nondestructive measurement of mill-scale thickness on steel by terahertz time-of-flight tomography

Zhai, Min, Alexandre Locquet, Cyrielle Roquelet, Patrice Alexandre, Laurence Daheron, and D. S. Citrin. "Nondestructive measurement of mill-scale thickness on steel by terahertz time-of-flight tomography." Surface and Coatings Technology (2020): 125765.

Abstract

We measure in a nondestructive and noncontact fashion the thicknesses of three scale films with thicknesses 28.5 ± 1.4 μm, 13.4± 0.9 μm, and 5.1 ± 0.3 μm on steel substrates employing terahertz time-of-flight tomography combined with advanced signal-processing techniques. Wüstite is the dominant phase in the scale films, though magnetite and hematite are also present. Because wüstite is electrically insulating, the incident terahertz electromagnetic pulses largely penetrate into the scale film; however, the pulses are entirely reflected by the underlying electrically conductive steel substrate. Because the film layers are thin, in some cases optically thin, the distinct pulses reflected at the air/scale and scale/steel interfaces overlap in time and thus are not visually evident in the reflected terahertz signal, necessitating the use of deconvolution techniques to recover the sample structure. We compare the merits of three deconvolution techniques, one unsuccessful (frequency-wavelet domain deconvolution) and two successful (sparse deconvolution and autoregressive extrapolation), to characterize the thicknesses of these scale films.

for full paper see  https://www.sciencedirect.com/science/article/abs/pii/S0257897220304345

ExperimentalThe THz experiments were carried out in an air -conditioned laboratory at 22 o C with humidity < 48 %. Otherwise, the samples were stored in a dry box to retard the transformation of wüstite from transforming into magnetite. The experiments shown here were conducted within the 3 months of sample fabrication to ensure that the scale films were primarily composed of wüstite. The THz reflection measurements are taken on a TeraView TPS Spectra 3000, a pulsed, broadband THz time -domain spectroscopy (TDS) system, shown in Fig. 4. 

Terahertz Imaging and Characterization Protocol for Freshly Excised Breast Cancer Tumor

Vohra, Nagma, Tyler Bowman, Keith Bailey, and Magda El-Shenawee. "Terahertz Imaging and Characterization Protocol for Freshly Excised Breast Cancer Tumors." Journal of Visualized Experiments 158 (2020).

This manuscript presents a protocol to handle, characterize, and image freshly excised human breast tumors using pulsed terahertz imaging and spectroscopy techniques. The protocol involves terahertz transmission mode at normal incidence and terahertz reflection mode at an oblique angle of 30°. The collected experimental data represent time domain pulses of the electric field. The terahertz electric field signal transmitted through a fixed point on the excised tissue is processed, through an analytical model, to extract the refractive index and absorption coefficient of the tissue. Utilizing a stepper motor scanner, the terahertz emitted pulse is reflected from each pixel on the tumor providing a planar image of different tissue regions. The image can be presented in time or frequency domain. Furthermore, the extracted data of the refractive index and absorption coefficient at each pixel are utilized to provide a tomographic terahertz image of the tumor. The protocol demonstrates clear differentiation between cancerous and healthy tissues. On the other hand, not adhering to the protocol can result in noisy or inaccurate images due to the presence of air bubbles and fluid remains on the tumor surface. The protocol provides a method for surgical margins assessment of breast tumors.

for full paper see https://cpb-us-e1.wpmucdn.com/wordpressua.uark.edu/dist/6/250/files/2016/05/jove-protocol-61007-terahertz-imaging-characterization-protocol-for-freshly-excised.pdf

Application of Terahertz Spectroscopy and Imaging in the Diagnosis of Prostate Cancer

Zhang, Ping, Shuncong Zhong, Junxi Zhang, Jian Ding, Zhenxiang Liu, Yi Huang, Ning Zhou, Walter Nsengiyumva, and Tianfu Zhang. "Application of Terahertz Spectroscopy and Imaging in the Diagnosis of Prostate Cancer." Current Optics and Photonics 4, no. 1 (2020): 31-43.

Abstract

The feasibility of the application of terahertz electromagnetic waves in the diagnosis of prostate cancer was examined. Four samples of incomplete cancerous prostatic paraffin-embedded tissues were examined using terahertz spectral imaging (TPI) system and the results obtained by comparing the absorption coefficient and refractive index of prostate tumor, normal prostate tissue and smooth muscle from one of the paraffin tissue masses examined were reported. Three hundred and sixty cases of absorption coefficients from one of the paraffin tissues examined were used as raw data to classify these three tissues using the Principal Component Analysis (PCA) and Least Squares Support Vector Machine (LS-SVM). An excellent classification with an accuracy of 92.22% in the prediction set was achieved. Using the distribution information of THz reflection signal intensity from sample surface and absorption coefficient of the sample, an attempt was made to use the TPI system to identify the boundaries of the different tissues involved (prostate tumors, normal and smooth muscles). The location of three identified regions in the terahertz images (frequency domain slice absorption coefficient imaging, 1.2 THz) were compared with those obtained from the histopathologic examination. The tissue tumor region had a distinctively visible color and could well be distinguished from other tissue regions in terahertz images. Results indicate that a THz spectroscopy imaging system can be efficiently used in conjunction with the proposed advanced computer-based mathematical analysis method to identify tumor regions in the paraffin tissue mass of prostate cancer.

for full paper see https://www.osapublishing.org/copp/abstract.cfm?uri=copp-4-1-31

Terahertz Imaging and Spectroscopy Data Acquisition 

All prostate tissue were tested using a TPI system (TeraPulse 4000, TeraView, Cambridge, England) operating in Reflection Spectrum and Imaging Module (RIM). This module adopts a single-point scanning imaging method. A raster-scanning system that changes the position of the sample through a mobile station in an X-Y plane was used, which allowed the terahertz radiation to pass through the individual points of the sample to be measured. The maximum size of the sample that the system can scan is 20 mm * 20 mm, and the minimum scanning step is 0.1 mm. The axial resolution of our TPI system used is around 30 microns and the maximum lateral resolution is around 250 microns. In this study, the scanning area of the sample was about 15 * 5 mm, the resolution of each point was 0.2 mm, and the diameter of the terahertz spot at the focal point is 0.2 mm

Laser process of transparent conducting surfaces for terahertz bandpass ultrathin metamaterials.

Wang, Qinghua, Bingtao Gao, Fatima Toor, Mark Arnold, and Hongtao Ding. "Laser process of transparent conducting surfaces for terahertz bandpass ultrathin metamaterials." In Laser-based Micro-and Nanoprocessing XIV, vol. 11268, p. 112680H. International Society for Optics and Photonics, 2020.

Abstract

Terahertz (THz) optoelectronics have great potentials in communication, imaging, sensing and security applications. However, the state-of-the-art fabrication processes for THz devices are costly and time-consuming. In this work, we present a novel laser-based metamaterial fabrication (LMF) process for high-throughput fabrication of transparent conducting surfaces on dielectric substrates such as quartz and transparent polymers to achieve tunable THz bandpass filtering characteristics. The LMF process comprises two steps: (1) applying ultrathin-film metal deposition, with a typical thickness of 10 nm, on the dielectric substrate; (2) creating periodic surface pattern with a feature size of ~100 microns on the metal film using nanosecond pulsed laser ablation. Our results demonstrate the LMF-fabricated ultra-thin metal film exhibits newly integrated functionalities: (a) highly conductive with sheet resistance of ~20 Ω/sq; (b) optically transparent with visible transmittance of ~70%; (c) tunable bandpass filtering effect in the THz frequency range; and (d) extraordinary mechanical durability during repeated fatigue bending cycles. The scientific findings from this work will render an economical and scalable manufacturing technique capable of treating large surface area for multi-functional THz metamaterials.

for full paper see https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11268/112680H/Laser-process-of-transparent-conducting-surfaces-for-terahertz-bandpass-ultrathin/10.1117/12.2544054.short

Experimental

… 2.5 THz Transmission Measurement Experimental THz transmission spectra, were generated using THz-Time Domain Spectroscopy (THz-TDS) technique 52,53. A 1000D TeraView spectrometer (TeraView Limited, Cambridge)

Optical thickness of a plant leaf measured with THz pulse echoes

Abautret, Yannick, Dominique Coquillat, Myriam Zerrad, Ryad Bendoula, Gabriel Soriano, Daphné Héran, Bruno Grèzes-Besset, Frédéric Chazallet, and Claude Amra. "Optical thickness of a plant leaf measured with THz pulse echoes." In Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications XIII, vol. 11279, p. 112790L. International Society for Optics and Photonics, 2020.

Abstract

We analyze Terahertz (THz) echoes by reflection on a sunflower leaf in order to evaluate the internal leaf structure (geometry, complex indices and thicknesses). The analysis is based on the thin film multilayer formalism in time and frequency domains. A high agreement is emphasized between experiment and theory, and we evaluate how realistic the multilayer solution can be in regard to our knowledge related to the sunflower leaf. A test campaign is performed in Charles Coulomb laboratory, which is equipped with the THz spectrometer.

for full paper see https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11279/112790L/Optical-thickness-of-a-plant-leaf-measured-with-THz-pulse/10.1117/12.2543710.short?SSO=1

Experimental

… 2.1 Terahertz Time Domain Spectroscopy (TTDS) In this study we performed the measurements campaign on a Terapulse 4000 spectrometer (TeraView Ltd., Cambridge, UK) with a femto-second fibre laser light source and a …

N-glycosylation state of TRPM8 protein revealed by terahertz spectroscopy and molecular modelling

Mernea, Maria, Roxana Ulăreanu, Octavian Călboreanu, Gabriela Chiritoiu, Dana Cucu, and Dan Mihăilescu. "N-glycosylation state of TRPM8 protein revealed by terahertz spectroscopy and molecular modelling." Biochimica et Biophysica Acta (BBA)-General Subjects (2020): 129580.

Abstact

TRPM8 member of the TRP superfamily of membrane proteins participates to various cellular processes ranging from Ca2+ uptake and cold sensation to cellular proliferation and migration. TRPM8 is a large tetrameric protein with more than 70% of its residues located in the cytoplasm. TRPM8 is N-glycosylated, with a single site per subunit. This work focuses on the N-glycosylation of TRPM8 channel that was previously studied by our group in relation to proliferation and migration of tumoral cells. Here, experimental data performed with deglycosylating agents assess that the sole glycosylation site contains complex glycans with a molecular weight of 2.5 kDa. The glycosylation state of TRPM8 in cells untreated and treated with a deglycosylating agent was addressed with Terahertz (THz) spectroscopy. Results show a clear difference between cells comprising glycosylated and deglycosylated TRPM8, the first presenting an increased THz absorption. Human TRPM8 was modelled using as templates the available TRPM8 and other TRPM channels structures. Glycosylations were modelled by considering two glycan structures with molecular weight close to the experiment: shorter and branched at the first sugar unit (glc1) and longer and unbranched (glc2). Simulation of THz spectra based on the molecular dynamics of unglycosylated and the two glycosylated TRPM8 models in lipid membrane and solvation box showed that glycan structure strongly influences the THz spectrum of the channel and of other components from the simulation system. Only spectra of TRPM8 with glc1 glycans were in agreement with the experiment, leading to the validation of glc1 glycan structure.

for full paper see https://www.sciencedirect.com/science/article/abs/pii/S0304416520300854

Experimental

… corresponding enzymes. 2.3. THz spectroscopy measurements. Transmission THz time-domain spectroscopy measurements were performed using a TPS Spectra 3000 spectrometer (TeraView Limited, Cambridge). The analysed … 

Advanced Packaging fault isolation case studies and advancement of Electro Optical Terahertz Pulse Reflectometry (EOTPR)

EOTPR is a well-established non-destructive fault isolation tool for advanced IC devices. These examples will show how EOTPR has been implemented to investigate a wide range of advanced package types, including 2.5D and 3D packages, wafer level fanout packages, and microelectromechanical (MEMs) devices. Further, we present the recent improvements to the EOTPR instrument and the results from a novel modelling approach that has the potential of vastly speeding up the fault localisation analysis.

Electro-Optical Terahertz Pulse Reflectometry (EOTPR) is an implementation of the time domain reflectometry (TDR) technique at terahertz frequencies, proven to enhance fault isolation accuracy to better than 10 µm. As in conventional TDR, the fault detection accuracy of EOTPR is a function of the rise time of the incident pulse, the time-based jitter, and signal-to-noise ratio (SNR). The EOTPR instrument generates a terahertz pulse using an ultrafast laser and a pair of photoconductive switches for signal generation and detection, resulting in a system with (i) high measurement bandwidth, (ii) low time-base jitter, and (iii) a high time-base resolution.

Compared to conventional TDR, EOTPR generates signals with faster rise time, has greater SNR, and a much-reduced time base jitter; system properties that offer the potential for a significantly increased distance-to-defect accuracy.A schematic diagram of the EOTPR system is shown below.

During operation, pulses are launched into a device-under-test (DUT) via a high frequency circuit probe. Portions of the pulse are reflected as it encounters changes in impedance, such as dead opens, resistive opens, and short circuit defects, within the IC. These reflections are measured by the detector photoconductive switch and are recorded as a function of time, resulting in the EOTPR waveform. An example waveform for an open high frequency probe is shown below.

As EOTPR utilises an impulse response rather than the step response of conventional TDR, high and low impedance discontinuities in a DUT result in positive peaks and negative troughs, respectively, in the measured waveform. The magnitude of these features indicates the size of the impedance change encountered by the pulse and their arrival time gives the location of the fault. EOTPR is, by necessity, a comparative technique; to understand whether a waveform feature arises from a fault in the DUT, it is essential to compare the waveform from a known good device (KGD).

To localise a fault within the DUT the time-domain waveform can be readily converted into the distance-domain. This can be accurately achieved by measuring reference devices that have impedance features, such as opens, at known locations. The effective dielectric constant of the DUT can be determined by measuring the time required for the EOTPR signal to travel between reference features or known locations, which is then used to convert the EOTPR waveform from time to distance.

EOTPR is now a well-established technique in failure analysis workflows and has been used to interrogate a wide range of different device architectures. Examples below show how EOTPR can be used to accurately localise faults in advanced IC packages.

For more information see https://teraview.com/eotpr/

Broadband amplitude, frequency, and polarization splitter for terahertz frequencies using parallel-plate waveguide technology.

Hernandez-Serrano, A. I., Daniel M. Mittleman, and Emma Pickwell-MacPherson. "Broadband amplitude, frequency, and polarization splitter for terahertz frequencies using parallel-plate waveguide technology." Optics Letters 45, no. 5 (2020): 1208-1211.

In this Letter, we report a broadband frequency/polarization demultiplexer based on parallel-plate waveguides (PPWGs) for terahertz (THz) frequencies. The fabrication and experimental validation of this polarization sensitive demultiplexer is demonstrated for the range from 0.2 to 1 THz. Upgrading the demultiplexer by adding a second demultiplexer stage, a fifty-fifty amplitude splitter is also demonstrated in the same frequency range. The multiplexer is based on a stainless-steel traveling-wave antenna, exhibiting strong mechanical robustness. This unique device exhibits three splitting mechanisms in the same device: amplitude, polarization, and frequency splitting. This is a significant improvement for the next generation of THz passive components for communication purposes.

 

for full paper see https://www.osapublishing.org/DirectPDFAccess/1FCF933A-FD44-4969-864AE73B77DF7F1F_427763/ol-45-5-1208.pdf?da=1&id=427763&seq=0&mobile=no

"To characterize the proposed demultiplexer, we use the Terapulse 4000 THz-TDS spectrometer from TeraView Ltd. with a spectral resolution of 4.5 GHz in the configuration shown in Fig. 2. This setup allows for the angle variation between the exit face of the demultiplexer and the receiver. An aperture size of 2.5 mm is placed in front of the receiver in order to improve the spatial resolution. In this Letter, we study two demultiplexers with two different values of the plate spacing in order to highlight the tunability of the device. In Fig. 3, the experimental results for the two demultiplexers are presented for both TE1 and TEM modes. "

Guided terahertz pulse reflectometry with double photoconductive antenna

Pan, Mingming, Quentin Cassar, Frédéric Fauquet, Georges Humbert, Patrick Mounaix, and Jean-Paul Guillet. "Guided terahertz pulse reflectometry with double photoconductive antenna." Applied optics 59, no. 6 (2020): 1641-1647.

Abstract

Developments toward the implementation of a terahertz pulse imaging system within a guided reflectometry configuration are reported. Two photoconductive antennas patterned on the same LT-GaAs active layer in association with a silica pipe hollow-core waveguide allowed us to obtain a guided optics-free imager. Besides working in a pulsed regime, the setup does not require additional optics to focus and couple the terahertz pulses into the waveguide core, simplifying the global implementation in comparison with other reported guided terahertz reflectometry systems. The system is qualified for imaging purposes by means of a 1951 USAF resolution test chart. An image resolution, after a 53 mm propagation length, by about 0.707 LP/mm over the 400–550 GHz integrated frequency band, was obtained, thus providing a promising basis to pursue efforts toward compact guided pulse imagers for sample inspection within the terahertz range.

for full paper see https://www.osapublishing.org/ao/abstract.cfm?uri=ao-59-6-1641

 "By using a fiber TDS system (TPS4000, TeraView Ltd., Cambridge UK), two waveguides with different lengths (201 and 301 mm, respectively) have been characterized in transmission-mode configuration"

A Nondestructive Eggshell Thickness Measurement Technique Using Terahertz Waves

Khaliduzzaman, Alin, Keiji Konagaya, Tetsuhito Suzuki, Ayuko Kashimori, Naoshi Kondo, and Yuichi Ogawa. "A nondestructive eggshell thickness Measurement technique Using terahertz Waves." Scientific reports 10, no. 1 (2020): 1-5.

Abstract

Eggshells play a number of important roles in the avian and reptile kingdom: protection of internal contents and as a major source of minerals for developing embryos. However, when researching these respective roles, eggshell thickness measurement remains a bottleneck due to the lack of a non-destructive measurement techniques. As a result, many avian and reptile research protocols omit consideration of eggshell thickness bias on egg or embryo growth and development. Here, we validate a non-destructive method to estimate eggshell thickness based on terahertz (THz) reflectance spectroscopy using chicken white coloured eggs. Since terahertz waves are reflected from outer air-eggshell interface, as well as the inner eggshell-membrane boundary, the resulting interference signals depend on eggshell thickness. Thus, it is possible to estimate shell thickness from the oscillation distance in frequency-domain. A linear regression-based prediction model for non-destructive eggshell thickness measurement was developed, which had a coefficient of determination (R2) of 0.93, RMSEP of 0.009, RPD of 3.45 and RER 13.67. This model can estimate eggshell thickness to a resolution of less than 10 μm. This method has the potential to expand the protocols in the field of avian and reptile research, as well as be applied to industrial grading of eggs.

For full paper see https://www.nature.com/articles/s41598-020-57774-5

"The intact eggs were measured using terahertz time-domain spectroscopy (THz-TDS, model: TPS spectra 3000, TeraView Ltd., UK) shown in Fig. 3. The eggs were irradiated by a THz pulse with an incident angle of 13 degrees. Following this, the reflected time-domain signal from the egg was obtained and reflectance calculated using a Blackman-Harris window function18. We then performed a fast Fourier transformation (FFT)."

Contactless Terahertz Paint Thickness Measurements: specificity of aeronautics industry

Chopard, Adrien, J. Bou Sleiman, Q. Cassar, P. Fauché, J. P. Guillet, P. Mounaix, M. Pan, J. B. Perraud, and A. Susset. "Contactless Terahertz Paint Thickness Measurements: specificity of aeronautics industry." (2019).

Abstract 

We report on numerical developments for the analysis of multilayered structures and the extraction of individual layer properties obtained by terahertz time domain measurements. An iterative algorithm implements a connected propagation tree which denotes the occurrence of the incident pulse division for each reflection / transmission appearance at each interface encountered during the propagation. Each sub pulse is individually monitored and its carried proportion of the incident power is extracted. Such a process allows to obtain the specific dielectric properties of each layer but additionally permits to derive a parametric transfer function describing the whole interaction with an incident beam. Procedure results performed on aeronautics multilayered painting samples are reported. 

for full paper see https://www.ndt.net/article/aero2019/papers/fp_we1a5_a_chopard.pdf

"The first step to achieve the simulations and the characterization, was to carefully extract the dielectric properties of each individual painting material (Tab. 1) via a basic inverse problem method thanks to measurements performed on a Teraview TPS 4000 system. Both the real and the imaginary part of the dielectric function are fitted with a first order Debye relaxation model. "

Low‐loss frequency selective surface for multi‐band THz transmission measurement

Yang, Xiaofan, Yonghu Zeng, Xiaoming Liu, Jun Zhou, Lu Gan, Hao Chen, and Junsheng Yu. "Low‐loss frequency selective surface for multi‐band THz transmission measurement." Microwave and Optical Technology Letters.

Abstract

Frequency selective surface is a key component in a quasi‐optical system enabling multi‐band operation. This work presents the design, fabrication and measurement of a low‐loss frequency selective surface in a quasi‐optical system for terahertz transmission measurement to separate 220 to 260 GHz and 325 to 340 GHz bands. High‐precision milling technique was employed for fabrication. The measurement was conducted using a terahertz time domain spectroscopy and a home‐made quasi‐optical test bench. Good agreement was achieved between the measured results and simulated ones. The design and measurement methods can be applied to frequency selective surfaces working in other millimeter wave bands.

for full paper see https://onlinelibrary.wiley.com/doi/full/10.1002/mop.32246

Application of a Terahertz System Combined with an X-Shaped Metamaterial Microfluidic Cartridge

Huang, Shih-Ting, Shen-Fu Hsu, Kai-Yuan Tang, Ta-Jen Yen, and Da-Jeng Yao. "Application of a Terahertz System Combined with an X-Shaped Metamaterial Microfluidic Cartridge." Micromachines 11, no. 1 (2020): 74.

Abstract

Terahertz (THz) radiation has attracted wide attention for its ability to sense molecular structure and chemical matter because of a label-free molecular fingerprint and nondestructive properties. When it comes to molecular recognition with terahertz radiation, our attention goes first towards the absorption spectrum, which is beyond the far infrared region. To enhance the sensitivity for similar species, however, it is necessary to apply an artificially designed metamaterial sensor for detection, which confines an electromagnetic field in an extremely sub-wavelength space and hence receives an electromagnetic response through resonance. Once the resonance is caused through the interaction between the THz radiation and the metamaterial, a minute variation might be observed in the frequency domain. For a geometric structure of a metamaterial, a novel design called an X-shaped plasmonic sensor (XPS) can create a quadrupole resonance and lead to sensitivity greater than in the dipole mode. A microfluidic system is able to consume reagents in small volumes for detection, to diminish noise from the environment, and to concentrate the sample into detection spots. A microfluidic device integrated with an X-shaped plasmonic sensor might thus achieve an effective and highly sensitive detection cartridge. Our tests involved not only measurements of liquid samples, but also the performance of a dry bio-sample coated on an XPS.

for full paper see https://www.mdpi.com/2072-666X/11/1/74

"The equipment for detection using THz time-domain spectroscopy (THz-TDS) is called a TeraPulse 4000 (product of TeraView, UK). The generation of terahertz pulsed radiation is based on a photoconductive switch in which terahertz photoconductive emitters rely on the production of fewcycle terahertz pulses using a femtosecond laser to excite a biased gallium arsenide antenna. This technique is inherently broadband, with the emitted power distributed over a frequency range from 60 GHz to 4 THz (wavenumber 2–133 cm−1 ). When demonstrating the measurement, the detection cartridge is installed at the fixed sample position in the chamber, as shown in Figure 3b. After setting up, the chamber is sealed and kept filled with dry air to eliminate any influence of water vapor. The spectrum"

EOTPR Electro Optical Terahertz Pulse Reflectometry: The world’s fastest and most accurate fault isolation system.

The EOTPR 4000 system is configured with an automated probe station which is capable of placing the probe tip to +/- 5 μm precision, while maintaining the EOTPR’s world leading sub-5 μm fault isolation accuracy.

This combination allows users to directly probe TSV tips and copper pillars.

Key Features

• Pre-scan station to map contact location and height.
• Data acquisition time of less than 5 seconds per pin.
• Software that will drive the automated probe station and pre-scan station.
• Availability of both manual mode and automated mode for probing.
• User interface software to manage data display and recipe creation.
• Probe tip placement.

for more information see https://teraview.com/eotpr/#tab|1