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Terahertz (THz) time-domain transmission spectroscopy was used to obtain the absorption coefficients and refractive indices of silica, Pyrex, and seven different Schott glasses. The refractive indices were analyzed using the Clausius–Mossotti equation, and the absorption coefficients in terms of the power-law model of far-infrared absorption. Relationships were observed between THz absorption and refractive indices on the one hand, and glass properties on the other. THz transmission data have been shown to provide a useful insight into glass structure. [ABSTRACT FROM AUTHOR]

Analyzes the hypersensitive phosphorus and fluoride transition of praseodymium ion in fluoride glasses. Important concerns in rear-earth doped glasses; Details of the experiment conducted; Emission spectra of hypersensitive transitions.

Presents a fluoroaluminate glasses developed as hosts for neodymium-doped fiber amplifier. Need for optical amplifiers in telecommunications; Experimental details; Viscosity and crystallization in fluoroaluminate glasses.

The relaxation time and absorption and emission profiles of the 0.59 THz TO phonon resonance in a ε-GaSe single crystal were measured using terahertz free induction decay, observed directly as a sequence of decaying sinusoidal oscillations in the time-domain signal following single-cycle pulse excitation. The phonon line profile was also measured using frequency-domain transmission with the resolution of 0.25 GHz and was found to be Lorentzian. [ABSTRACT FROM AUTHOR]

Terahertz time-domain spectroscopy (THz TDS) was used to investigate a series of chalcogenide glasses. In particular, the dielectric properties at terahertz frequencies were determined and correlated with the glass composition. The experimental results showed a strong relationship between the dielectric properties and the polarizability of the glasses studied. A new explanation based on the coordination number of the metallic cations was proposed to understand these observations. [ABSTRACT FROM AUTHOR]

High optical quality centimeter sized GaS crystals are grown using a modified vertical Bridgman method with heat field rotation of the growth melt. Ordinary and extraordinary wave refractive index dispersions are studied by THz time-domain spectroscopy (THz-TDS). New dispersion equations are designed to be suitable for estimating dispersion properties of solid solution GaSe1-xSx crystals from the near IR through the mid-IR and further into the THz range. [ABSTRACT FROM AUTHOR]

Abstract: We present an etalon-based method of calibrating the frequency of terahertz time-domain spectrometers (THz TDS). The method utilizes the etalon effect produced by multiple reflections in non-absorbing wafers or in narrow air–gaps. The technique provides frequency calibration across the measurement band with uncertainties comparable with the typical THz TDS resolution. [Copyright &y& Elsevier]

Abstract: We present a simple algorithm for removing or reducing spurious oscillations in the THz spectra which result from secondary reflection peaks in samples or optical elements. The algorithm utilizes the fact that a THz time-domain trace containing secondary peaks can be represented as a convolution of the primary peak and two or more delta functions. The algorithm is applicable for samples which are sufficiently thick that the reflection peak does not overlap with the primary peak, and that do not have strong absorption or dispersion. [Copyright &y& Elsevier]

Abstract: Terahertz time-domain transmission spectroscopy was used to obtain the absorption coefficients and refractive indices of polycrystalline quartz, amorphous silica, Pyrex and BK7 glasses. The results were analyzed in terms of the power-law model of far-infrared absorption. Evidence of the Boson peak was seen in the absorption spectra. Relationships were observed between THz absorption and refractive indices on the one hand, and glass structure and properties on the other. THz TDS is demonstrated to be a useful tool in the study of far-infrared transmission properties of glasses, producing low-noise, high resolution measurements of absorption coefficients and refractive indices. [Copyright &y& Elsevier]

Photoluminescence at wavelengths between 600 and 660 nm was observed in Pr3+-doped GeS2-based glasses. The spectral profile of the 3P0→3H6 transition was found to be highly sensitive to the presence of oxide impurities in the glass. The main peak at 632 nm was identified with sulphide-dominated dopant sites, while the shoulder at 614 nm was attributed to oxide-dominated sites. Results demonstrate that the luminescence spectrum of Pr3+ at 610–635 nm reveals the presence and concentration of oxygen-rich sites in Pr3+-doped GeS2-doped glasses. The method is shown to be sensitive to concentrations of Ge&z.sbnd;O bonds down to 200 ppmw level. [Copyright &y& Elsevier]

Abstract: Terahertz frequency transmission measurements on ceramic boron nitride and aluminium nitride are described. The absorption coefficients and refractive indices of these materials show that they have high terahertz transparency, which together with their high melting temperatures and mechanical strength makes them particularly suitable for use as THz windows in high pressure and/or high temperature applications. [Copyright &y& Elsevier]

We comment on the recent paper by V.D. Antsygin et al. [Opt. Commun. 309 (2013) 333–337], in which for the first time dispersions of refractive indices n x , z in lithium triborate (LBO) were presented for the THz domain. Their claim of “ n x > n z ”, based on measurements by THz time-domain spectroscopy (TDS), is contrary to the well-known relationship for the maximum transparency region. [ABSTRACT FROM AUTHOR]

A method to quantify the linearity and dynamic range of terahertz detectors is reported and used to show that terahertz time-domain-spectrometers exhibit a nonlinear amplitude response at frequencies below 1.5 THz. [ABSTRACT FROM AUTHOR]

A simple scheme for generating continuous-wave (CW) terahertz (THz) radiation from a two-colour laser is reported. A Ti-sapphire laser is forced to oscillate on two modes by placing a Fabry-Perot etalon in the laser cavity. THz radiation is generated by photomixing in a biased photoconverter. The THz frequency is determined by the separation of the etalon plates. [ABSTRACT FROM AUTHOR]

GaSe 1−x S x (x = 0, 0.01, 0.05, 0.13, 0.22, 0.29, 0.44) crystals were grown by modified vertical Bridgman method that provided (0001) crystal plane orientation perpendicular to growth axis. Absorption coefficient is minimal (decreased by up to 3 times) in the THz range at the optimal S-doping of 3 weight % (x = 0.13). Increased S content causes the absorption coefficient for e-wave to become frequency independent in the main part of the spectrum from 0.3 to 3 THz. A narrow line-width rigid phonon absorption peak E ″(2) at 1.79 THz arises and then declines in intensity with the doping level, in parallel with a shift towards shorter wavelength. [ABSTRACT FROM AUTHOR]

Abstract: Layered clay minerals from the smectite group with different chemical composition and resulting layer charge (e.g. pyrophyllite, illite, hectorite and montmorillonite) were characterised for their dielectric properties in the far-infrared region using terahertz-time domain spectroscopy (THz-TDS). Samples with distinct cation exchange capacity such as hectorite and montmorillonite were modified using cation exchange reaction with alkylamines or amino acids. The presence of these species in 2D gallery was proved by X-ray diffraction and Fourier transform infrared spectroscopy. The frequency-dependent refractive index of these minerals was determined in the experimentally accessible range of 0.1–3.0 THz (3–100 cm−1) using THz-TDS. Pristine samples revealed their refractive indices to be 1.82–2.15 at about 1 THz while the modified montmorillonite samples had their refractive indices changed by organic molecules used for their modification to 1.70–2.35 for amines and 1.97–2.36 for amino acids. The presence of organic substances in 2D gallery of clays was detectable despite the relatively high absorption of smectites with magnitude of 100 cm−1. [Copyright &y& Elsevier]

[Display omitted] Over the past decade, continuous manufacturing has garnered significant attention in the pharmaceutical industry. Still, numerous continuous unit operations need developments, such as powder blending and feeding at low and high throughputs. Especially the continuous and consistent feeding of solid drug substances and excipients at low feed rates remains challenging. This study demonstrates a micro-feeder capable of feeding poorly-flowing pharmaceutical powders at low feed rates. The system performance was investigated using three grades of pharmaceutical powder: croscarmellose sodium (cohesive), magnesium stearate (very cohesive), and an active ingredient, paracetamol (non-flowing). The results show that the micro-feeder can continuously and consistently feed powders at low flow rates (<20 g/h) with low variability (<10 % for non-flowing materials and < 5 % for cohesive materials). Notably, the micro-feeder achieves these results without any feedback control and remains unaffected by refilling, making it a truly versatile and industry-relevant solution. The study's results demonstrate that this micro-feeder system effectively tackles the challenge of consistent and accurate powder feeding at low rates. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two novel methods used to determine renewable energy content and yield from mixed waste materials. [•] Biogenic content of waste components measured, along with proximate and ultimate analysis. [•] Determined values accurate to within 5% of actual values. [•] Key applications include renewable energy yield prior to combustion and classification of SRF. [ABSTRACT FROM AUTHOR]

Abstract: Terahertz time-domain spectroscopy measurements were made for vertically aligned multi-walled carbon nanotube (VACNT) films. We obtained the frequency dependent complex permittivity and conductivity (on the assumption that permeability μ =1) of several samples exhibiting Drude behaviour for lossy metals. The obtained material properties of VACNT films provide information for potential microwave and terahertz applications. [Copyright &y& Elsevier]

THz optical properties of lithium borate (LBO) crystals were measured using time-domain spectroscopy (TDS). The LBO crystal samples were of high optical quality and were cut and polished along the 〈100〉, 〈010〉 and 〈001〉 axes. Two independent measurements were performed in order to confirm the reproducibility and consistency of results. The contradictions in the previously published data on the THz optical properties of LBO were clarified. It was shown that the birefringence order at THz frequencies is n z < n x < n y , whereas at optical frequencies it is known to be n x < n y < n z . It was seen that n z , which has the highest value in the visible, has the lowest value at THz. This is explained in terms of ionic polarizability and is consistent with the fact that the THz absorption coefficient for a wave polarized along the Z -axis is more than an order of magnitude lower than for the X and Y axes. Absorption as low as 0.2 cm −1 was found at frequencies up to 0.5 THz for a wave polarized parallel to the Z -axis. A set of new dispersion equations was designed for the entire transparency range. [ABSTRACT FROM AUTHOR]

[Display omitted] Consistent powder micro-feeding (<100 g/h) is a significant challenge in manufacturing solid oral dosage forms. The low dose feeding can well control the content consistency of the dosage forms, which improves drug efficiency and reduces manufacturing waste. Current commercial micro-feeders are limited in their ability to feed < 20 g/h of cohesive (i.e. powders of poor flowability) active pharmaceutical ingredients (API) and excipients (e.g. lubricants) with low fluctuation. To breach this gap, this study presents an advanced micro-feeder design capable of feeding a range of pharmaceutical-grade powders consistently at flow rates as low as 0.7 g/h with <20 % flow rate variation. This was possible due to a novel powder conveying concept utilising particle re-entrainment to minimise flow rate variations. This work details the design of this pneumatic micro-feeder and its excellent micro-feeding performance even for cohesive powders. The experimental studies investigated the influence of the process parameters (air pressure and air flow rate) and equipment configurations (insert size and plug position) on the feeding performance of different pharmaceutical-relevant powders, i.e., microcrystalline cellulose (MCC), croscarmellose sodium (CCS), crospovidone (XPVP) and paracetamol (APAP). It was shown that the system is capable of delivering consistent powder flow rates with good repeatability and stability. [ABSTRACT FROM AUTHOR]

Abstract: We present excited state absorption (ESA) spectroscopy of Nd3+-activated fluoroaluminate glass. The ESA spectra were measured in the range from 550 to 1800nm by the continuous-wave pump-probe technique. Judd–Ofelt (JO) formalism was employed to interpret the results. The obtained intensity parameters and linewidths were used to simulate the ESA spectra, which were successfully compared with the experimental data. The calculated ESA spectra were also used to precisely assign previously observed upconverted emissions and to predict additional ones, which were experimentally verified. The presented upconverted luminescence spectrum contains several anti-Stokes emission lines at 355nm, 381nm, 412nm and 448nm, and is in good agreement with the calculations. [Copyright &y& Elsevier]

Abstract: We report on the upconverted luminescence in neodymium-activated fluoroaluminate glass obtained with 800nm diode laser excitation. Several anti-Stokes emissions: at 588, 607, 720 and 750nm are observed and appropriate transitions are assigned. For both latter emissions we observe strong dependence on temperature: the 720nm emission intensity decreases with temperature, whereas the 750nm emission increases. Interpretations are presented in terms of the influence of oxygen-affected sites on the radiationless transitions and multiphonon anti-Stokes excitation. The models provide reasonable fits to the experimental data. [Copyright &y& Elsevier]

Abstract: We demonstrate how the existence of the oxygen-affected sites in the glass matrix of the Pr3+—activated fluoroaluminate glass reflects the unusual decay time dependence on the emission wavelength. The previously proposed model of the “defect state” has been redefined, developed and used to describe the wavelength dependence of the emission decays of three different emission bands. The model allows reasonably good fits to the experimental data. [Copyright &y& Elsevier]

The accurate measurement of the permittivity, loss tangent and dielectric anisotropy DC bias dependence for two different liquid crystal (LC) materials in the frequency range 140-165 GHz is described. The electrical characteristics are obtained by curve fitting computed transmission coefficients to the experimental spectral response of a new class of electronically reconfigurable frequency selective surface. The periodic structure is designed to yield bandpass filter characteristics with and without an applied bias control voltage in order to measure the tunability of the LC material which is inserted in a 705 µm-thick cavity. [ABSTRACT FROM AUTHOR]