Optimization of THz diffractive optical elements thickness

Surma, Mateusz, Izabela Ducin, Maciej Sypek, Przemyslaw Zagrajek, and Agnieszka Siemion. "Optimization of THz diffractive optical elements thickness." Photonics Letters of Poland 10, no. 4 (2018): 115-117.

Abstract

Diffractive optical elements (DOEs) are strictly related to the design wavelength due to the fact that they must introduce particular phase delay of the wavefront propagating through the structure. Mostly the attenuation of the material is not taken into account. In this article we propose to optimize thickness of the DOE by reducing introduced phase retardation but also attenuation. The efficiency of DOEs is determined by the method of coding phase distribution and can be easily measured by using diffraction orders of corresponding diffraction grating. Here, we analyze binary phase diffraction gratings with assumed attenuation. 

For full paper see http://www.photonics.pl/PLP/index.php/letters/article/view/10-41

… The designed gratings were manufactured in a 3D printing technique in paper using an MCor Iris printer [15]. Prior to the design process was the determination of the material optical properties. Time Domain Spectroscopy (TDS ‒ TeraView) was used for this task … 

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, AI HERNANDEZSERRANO, and E. M. M. A. PICKWELL-MACPHERSON. "Utilizing multilayer structures to enhance terahertz characterization of thin films ranging from aqueous solutions to histology slides." Optics Letters

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 tissues are 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/upcoming_pdf.cfm?id=359791

.......The Srefl lines are calculated by Eqn (3), light green and light blue lines are calculated by Eqn (2) and Eqn (1), respectively. The TF liquid measurements were conducted using the Terapulse 4000 from Teraview …

Terahertz pulse time-domain holography method for phase imaging of breast tissue

Balbekin, Nikolay S., Quentin Cassar, Olga A. Smolyanskaya, Maksim S. Kulya, Nikolay V. Petrov, Gaetan MacGrogan, Jean-Paul Guillet, Patrick Mounaix, and Valery V. Tuchin. "Terahertz pulse time-domain holography method for phase imaging of breast tissue." In Quantitative Phase Imaging V, vol. 10887, p. 108870G. International Society for Optics and Photonics, 2019.

Abstract

Pulse holographic imaging along with time-domain spectroscopy scan and tomographic techniques are of great interest. Since the advantages of holography are the lack of focusing optics and high spatial resolution, and, comparing with tomography, less computation cost for numerical reconstruction, this technique is preferable for the analysis of thin histological samples. In this work we have created the experimental scheme that involves measurement of diffraction pattern of the collimated THz pulse field spatial distribution at some distance behind the object in the time-domain mode, thus allowing reconstruction of amplitude and phase distribution at the object plane by numerical backpropagation of the wavefront in the spectral domain. In our experiment, we used a breast biopsy sample containing cancer tissues, we also performed numerical simulations accounting for experimental conditions to confirm the conceptual applicability of the reconstruction method.

For full paper see https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10887/108870G/Terahertz-pulse-time-domain-holography-method-for-phase-imaging-of/10.1117/12.2508711.short?SSO=1

BREAST TISSUE PROBING 3.1 Material & Methods A commercially available TeraPulse4000 (TeraView Ltd, Cambridge, UK) configured in reflection geometry by the means of external added optics was used to probe freshly excised breast tissues … 

Terahertz Spectroscopy: An investigation of the Structural Dynamics of Freeze-Dried PLGA Microspheres

Hooper, Philippa J., Gabi Kaminski, and J. A. Zeitler. "Terahertz Spectroscopy: An investigation of the Structural Dynamics of Freeze-Dried PLGA Microspheres." (2019).

Abstract

Biodegradable poly lactic-co-glycolic acid (PLGA) microspheres can be used to encapsulate peptide and offer a promising drug delivery vehicle. In this work we investigate the dynamics of PLGA microspheres prepared by freeze-drying and the molecular mobility at lower temperatures leading to the glass transition temperature, using temperature-variable terahertz time-domain spectroscopy (THz-TDS) experiments. The microspheres were prepared using a water-in-oil-in-water (w/o/w) double emulsion technique and subsequent freeze-drying of the samples. Physical characterisation was performed by morphology measurements, scanning electron microscopy (SEM), and helium pycnometry. The THz-TDS data show two distinct transition processes, T_g,β in the range of 167-219 K, associated with local motions, and T_g,α in the range of 313-330 K associated with large-scale motions, for the microspheres examined. Using FTIR measurements in the mid-infrared we were able to characterise the interactions between a model polypeptide, exendin-4, and the PLGA copolymer. We observe a relationship between the experimentally determined T_g,β and T_g,α and free volume and microsphere dynamics. 

For full paper see https://europepmc.org/abstract/ppr/ppr66651

… Terahertz Time-Domain Spectroscopy (THz-TDS) The THz-TDS spectra were acquired using a commercial TeraPulse 4000 instrument across the spectral range of 0.2 − 2.2THz (TeraView, Cambridge, UK). The sample temper …

Insights into the structural dynamics of poly lactic-co-glycolic acid at terahertz frequencies

Shmool, Talia A., and J. Axel Zeitler. "Insights into the structural dynamics of poly lactic-co-glycolic acid at terahertz frequencies." Polymer Chemistry 10, no. 3 (2019): 351-361.

Abstract

The mechanical properties of an amorphous copolymer are directly related to the dynamic processes occurring at the molecular level. Poly lactic-co-glycolic acid (PLGA) is a biodegradable copolymer, and in this work we investigate the dynamics of PLGA and its glass transition behaviour by performing variable temperature terahertz time-domain spectroscopy (THz-TDS) experiments. We correlate PLGA dynamics, as measured at terahertz frequencies, their temperature dependence, molecular weight (MW), lactide toglycolide ratio, and free volume. The THz-TDS data can be used to detect two distinct transition processes, Tβ and Tg,α. To complement our analysis, we use dynamic mechanical analysis (DMA) to probe the β- and α-relaxation processes in PLGA, and compare the results obtained from the DMA experiments with those obtained using THz-TDS. The values of Tg,α, as determined from the THz-TDS experiments, are in good agreement with Tg,DSC, determined by calorimetric measurements, and with Tg,DMA, determined by the DMA measurements. We attribute Tβto the change in dipole moments associated with the β-relaxation process, originating from the local rotation of C–O macromolecular chain segments, and Tg,α to the change in dipole moments due to large segmental motion of the copolymer backbone associated with the α-relaxation process. By showing experimental temperature-dependent results from THz-TDS and DMA for PLGA, we demonstrate that the behaviour of PLGA is in line with the potential energy surface interpretation by Goldstein as well as the free volume theory of Fox and Flory, and that both concepts together can be used to understand amorphous polymers.

for full paper
see https://pubs.rsc.org/en/content/articlelanding/2018/py/c8py01210e/unauth#!divAbstract

… 0.50 mm in thickness. 1.2 Experimental setup. The THz-TDS spectra were acquired using a commercial TeraPulse 4000 instrument across the spectral range of 0.2–2.2 THz (TeraView, Cambridge, UK). The sample temperature …

Terahertz Spectroscopy and Quantum Mechanical Simulations of Crystalline Copper-Containing Historical Pigments

Kleist, Elyse M., Corinna L. Koch Dandolo, Jean-Paul Guillet, Patrick Mounaix, and Timothy M. Korter. "Terahertz Spectroscopy and Quantum Mechanical Simulations of Crystalline Copper-Containing Historical Pigments." The Journal of Physical Chemistry A (2019).

Abstract

Terahertz spectroscopy, a noninvasive and nondestructive analytical technique used in art conservation and restoration, can provide compelling data concerning the composition and condition of culturally valuable and historical objects. Terahertz spectral databases of modern and ancient artists’ pigments exist but lack explanations for the origins of the unique spectral features. Solid-state density functional theory simulations can provide insight into the molecular and intermolecular forces that dominate the observed absorption features as well as reveal deviations from simple harmonic vibrational behaviour that can complicate these spectra. The characteristic terahertz spectra of solid azurite, malachite, and verdigris are presented here, along with simulations of their crystalline structures and sub-3.0 THz lattice vibrations. The powerful combination of theory and experiment enables unambiguous spectral assignment of these complex materials and highlights the challenges that anharmonic peak broadening in organic-containing materials may present in the construction of reference pigment databases.

For full paper see https://pubs.acs.org/doi/abs/10.1021/acs.jpca.8b11676

… Terahertz spectra were measured on a TPS Spectra 3000 time-domain spectroscopy system from TeraView (Cambridge, UK) at room temperature (293 K). The system relies on GaAs laser-gated photoconductive antennas …

SU-8 based planar metamaterials with fourfold symmetry as selective terahertz absorbers

Grześkiewicz, B., A. Sierakowski, J. Marczewski, N. Pałka, and E. Wolarz. "SU-8 based planar metamaterials with fourfold symmetry as selective terahertz absorbers." Opto-Electronics Review 26, no. 4 (2018): 329-337.

Abstract

We report on the absorption properties of polarization-insensitive transmissive and reflective metamaterial absorbers based on two planar aluminium periodic structuresand SU-8 epoxy resist. These absorbers were investigated using numerical simulationand experimental methods in the terahertz range (below 2 THz). SU-8 is a very promising organic material for dielectric layers in planar metamaterials, because its application simplifies the process of fabricating these structures and significantly reduces the fabrication time. The experimental absorption of the metamaterial absorbers has narrowband characteristics that were consistent with the numerical simulations. Power flow analysis in the transmissive metamaterial unit cell shows that the absorption in the terahertz range occurs primarily in the SU-8 layer of the absorber.

Graphical abstract

for full paper https://www.sciencedirect.com/science/article/abs/pii/S1230340218300532

… Experimental transmittance, reflectance, and absorption spectra for the investigated TMAs were obtained for samples consisting of many unit cells. The spectra were measured using a TPS 3000 (Teraview) terahertz time-domain spectrometer purged with dry air … 

Multilayer film thickness measurement using ultrafast Terahertz pulsed imaging

Abdelsalam, Dahi Ghareab, Safaa Khalil, Hadeer Hamdy Abdelaziz Sherif, and Mohamed Elokr. "Multilayer film thickness measurement using ultrafast Terahertz pulsed imaging." Journal of Physics Communications (2019).

Abstract

Terahertz (THz) rays have higher penetration depth compared to visible rays, and hence can be effectively used to measure a geometric thickness of soft samples with no damage. Measurement of such soft samples with contact methods is a challenge in terms of accuracy and speed. In this paper, a terahertz pulsed imaging(TPI) imaga 3000 system with reflection imaging module has been employed to measure the individual soft thickness of a multilayer structure made of adhesive soft polymer films with temporal method. Automatic scan of the sample has been carried out and the echoes at each interface are sampled and then detected. The complex refractive index (RI) of the sample has been measured with terahertz pulsed spectra (TPS) 3000 with transmission module. To avoid the incorrect thickness from the measured complex RI due to dispersion, propagation constants of the sample for a given mode and polarization have been extracted by solving the Helmholtz equation, numerically. From the detected delay of echoes and the calculated propagation constants, the geometric thickness of each layer is calculated. Further thickness of an onion leaf as a biological sample was measured based on the propagation constant. Results showed good accuracy with uncertainty budget of 7% of the THz wavelength used.

For full paper see https://iopscience.iop.org/article/10.1088/2399-6528/ab0aa3/meta

… The arrival time difference of the reflected THz pulses is calculated with THz-TDS (TPI imaga 3000) system with reflection imaging module, while the complex RI of each layer is calculated with the TPS spectra 3000 (TeraView Ltd., Cambridge, UK) … 

Optical Functions of Methanol and Ethanol in Wide Spectral Range

Lesňák, Michal, Kamil Postava, František Staněk, and Jaromír Pištora. "Optical Functions of Methanol and Ethanol in Wide Spectral Range." In Advances in Signal Processing and Communication, pp. 479-489. Springer, Singapore, 2019.

Abstract

The motivation of this paper is to determinate the precise complex refractive indices dispersion of ethanol, methanol, and their solutions in the wide spectral range from 8 to 40 000 cm−1(wavelength range from 250 nm to 1.25 mm) in coupling to biosensors applications (body liquids analyses, tissue ethanol solutions testing, etc.) because a specification of the complex optical functions consistent with Kramers–Kronig dispersion relations in the whole mentioned spectral range was still missing. A general method combining UV/visible/near-infrared spectroscopy and Mueller matrix ellipsometry, Fourier transform infrared spectroscopy (FTIR), infrared attenuated total reflection (ATR) spectroscopy, and terahertz time-domain spectroscopy (THz-TDS) is proposed. The experimental data are modeled using a dielectric function parametrization based on the Brendel–Bormann oscillators.

for full paper see https://link.springer.com/chapter/10.1007/978-981-13-2553-3_46

… Optical properties in the terahertz spectral range were obtained using the terahertz time-domain spectroscopy (THz-TDS) TPS Spectra 3000 from TeraView. We have combined both ATR and transmission measurements … IEEE, pp 

Predicting capsule fill weight from in-situ powder density measurements using terahertz reflection technology

Stranzinger, Sandra, Eva Faulhammer, Jingyi Li, Runqiao Dong, J. Axel Zeitler, Stefano Biserni, Vittorio Calzolari, Johannes G. Khinast, and Daniel Markl. "Predicting capsule fill weight from in-situ powder density measurements using terahertz reflection technology." International Journal of Pharmaceutics: X 1 (2019): 100004.

Abstract

The manufacturing of the majority of solid oral dosage forms is based on the densification of powder. A good understanding of the powder behavior is therefore essential to assure high quality drug products. This is particularly relevant for the capsule filling process, where the powder bulk density plays an important role in controlling the fill weight and weight variability of the final product. In this study we present a novel approach to quantitatively measure bulk density variations in a rotating container by means of terahertz reflection technology. The terahertz reflection probe was used to measure the powder density using an experimental setup that mimics a lab-scale capsule filling machine including a static sampling tool. Three different grades of α-lactose monohydrate excipients specially designed for inhalation application were systematically investigated at five compression stages. Relative densities predicted from terahertz reflection measurements were correlated to off-line weight measurements of the collected filled capsules. The predictions and the measured weights of the powder in the capsules were in excellent agreement, where the relative density measurements of Lactohale 200 showed the strongest correlation with the respective fill weight (R2=0.995). We also studied how the density uniformity of the powder bed was impacted by the dosing process and the subsequent filling of the holes (with excipient powder), which were introduced in the powder bed after the dosing step. Even though the holes seemed to be filled with new powder (by visual inspection), the relative density in these specific segments were found to clearly differ from the undisturbed powder bed state prior to dosing. The results demonstrate that it is feasible to analyze powder density variations in a rotating container by means of terahertz reflection measurements and to predict the fill weight of collected capsules.

Graphical abstract

For full paper see https://www.sciencedirect.com/science/article/pii/S2590156718300045

… A commercial time-domain terahertz system (TeraPulse 4000, TeraView Ltd, Cambridge, UK) coupled with a fiber-based flexible reflection probe was used in this study. The system was configured to operate at an optical …

LIPOPOLYSACCHARIDES ASSOCIATION ON THE SURFACE OF A SILICON CRYSTAL ADDRESSED BY THz SPECTROSCOPY AND MOLECULAR MODELLING

JABERI, AKH, J. A. H. AL SAEDI, MARIA MERNEA, L. PETRESCU, O. CĂLBOREAN, I. VASILE, and DF MIHĂILESCU. "LIPOPOLYSACCHARIDES ASSOCIATION ON THE SURFACE OF A SILICON CRYSTAL ADDRESSED BY THz SPECTROSCOPY AND MOLECULAR MODELLING." Romanian Journal of Biophysics 29, no. 1 (2019).

Astract. 

Gram-negative bacteria lipopolysaccharides (LPS) are lipids with a chemical structure comprising a lipidic region with several hydrocarbonate chains and a large saccharide region. Due to their structure, LPS can associate through hydrophobic forces, but also can dissolve in water. Here we investigated the association of LPS molecules on the surface of a silicon crystal by terahertz (THz) spectroscopy. We measured the THz absorption of LPS molecules directly deposited on the crystal or deposited on the crystal coated with a CaCl2 solution. Resulting spectra present a non-linear increase of THz absorption, with two absorption shoulders at 1.05 THz (~35 cm–1 ) and 1.37 THz (~45 cm–1 ). The presence of the CaCl2 solution does not influence the shoulders localization, suggesting a similar association of LPS molecules in both situations. Based on the comparison with previous THz studies on phospholipid bilayers, we suggested a layer ordering of LPS molecules in our samples that was validated through molecular modelling methods. We modelled LPS monolayers and simulated the THz spectra by normal modes analysis (NMA) and molecular dynamics (MD). The NMA spectrum of a LPS monolayer resulted in agreement with experiments, allowing us to validate the proposed LPS layer organization and the spectra simulation method.

For full paper see https://www.rjb.ro/wp-content/uploads/Mernea_4_F.pdf

… LPS molecules (2 mg/mL) were dissolved into a 7:3 chloroform-methanol mixture [16]. THz spectra were recorded using a TPS spectra 3000 spectrometer (TeraView Ltd., United Kingdom) in attenuated total reflection (ATR) setup under continuous nitrogen purge …

Flexible terahertz and FarIR polymer‐supported filter

Sanphuang, Varittha, and Niru K. Nahar. "Flexible terahertz and FarIR polymer‐supported filter." Microwave and Optical Technology Letters 60, no. 11 (2018): 2801-2805.

Abstract

We present the design, fabrication, and measurement of a terahertz (THz) polymer‐supported filter. A periodic structure, frequency selective surfaces (FSS) is employed to provide bandpass characteristic for this filter design with polyimide (PI) film as a substrate. This PI film (13 μm thick) is very thin and thus provides a flexible support to the filter. The average extracted dielectric constant ε r is 3.35 and the average refractive index n s is 1.84. The final filter structure was fabricated using standard microfabrication process. The measured transmission response shows high percentage of transmission (~80%) with the peak at 0.58 THz and sharp roll‐off that covers the broad range of frequency from 0.1 to 1 THz (wavelength of 300 μm‐3000 μm).

For full paper see https://onlinelibrary.wiley.com/doi/abs/10.1002/mop.31414

… The transmission responses of these PI films were measured using a time domain THz spectroscopy (TPS3000, TeraView Ltd.) as shown in Figure 2. The transmission responses show high percentage of transmission starting …

Pulsed terahertz reflection imaging of tumors in a spontaneous model of breast cancer

Vohra, Nagma, Tyler Bowman, Paola M. Diaz, Narasimhan Rajaram, Keith Bailey, and Magda El-Shenawee. "Pulsed terahertz reflection imaging of tumors in a spontaneous model of breast cancer." Biomedical Physics & Engineering Express 4, no. 6 (2018): 065025.

Abstract

We report the use of reflection-mode terahertz (THz) imaging in a transgenic mouse model of breast cancer. Unlike tumor xenografts that are grown from established cell lines, these tumors were spontaneously generated in the mammary fat pad of mice, and are a better representation of human breast cancer. THz imaging results from 7 tumors that recapitulate the compartmental complexity of breast cancer are presented here. Imaging was first performed on freshly excised tumors within an hour of excision and then repeated after fixation with formalin and paraffin. These THz images were then compared with histopathology to determine reflection-mode signals from specific regions within tumor. Our results demonstrate that the THz signal was consistently higher in cancerous tissue compared with fat, muscle, and fibrous tissue. Almost all tumors presented in this work demonstrated advanced stages where cancer infiltrated other tissues like fat and fibrous stroma. As the first known THz investigation in a transgenic model, these results hold promise for THz imaging at different stages of breast cancer.

for full paper see https://iopscience.iop.org/article/10.1088/2057-1976/aae699/meta

… Experimental Terahertz Imaging System. Terahertz imaging in this work is performed
using a commercial THz system from TeraView, Ltd shown in the diagram in Fig. 2a. An
800 nm pulse from a Ti:Sapphire laser is passed through a beam splitter …