Terahertz spectra of a range of liquids

 

We show here the terahertz spectra of liquids.  These parameters can be measured on a terahertz spectrometer such as that provide by TeraView.

TeraView's TeraPulse Lx with sample chamber.

TeraView can provide a complete solution for your terahertz measurements.  The sample chamber can be purged with either dry air or nitrogen.  The software provides you with the 

• Reference and sample time domain signals
• Sample and reference spectrum and phase
• Transmittance
• Transmittance phase
• Absorbance
• Apodization functions
• Background subtraction

With the input of the sample thickness the user is able to obtain 

• Absorption coefficient
• Refractive index
• Complex refractive index

The absorption coefficient of the liquids is shown here

For more information please click here or visit www.teraview.com

Terahertz spectra of a range of window materials

Shown on this page is a selection of window materials that can be used in the terahertz region of the electromagnetic spectrum.  These parameters can be measured on a terahertz spectrometer such as that provide by TeraView.

TeraView's TeraPulse Lx with sample chamber.

TeraView can provide a complete solution for your terahertz measurements.  The sample chamber can be purged with either dry air or nitrogen.  The software provides you with the 

• Reference and sample time domain signals
• Sample and reference spectrum and phase
• Transmittance
• Transmittance phase
• Absorbance
• Apodization functions
• Background subtraction

With the input of the sample thickness the user is able to obtain 

• Absorption coefficient
• Refractive index
• Complex refractive index

Below at the refractive index of a number of window materials that can be used in the terahertz region. 

The absorption of these windows materials are shown here

For more information please click here or visit www.teraview.com

 

Terahertz Nondestructive Stratigraphic Analysis of Complex Layered Structures: Reconstruction Techniques

Zhai, Min, D. S. Citrin, and Alexandre Locquet. "Terahertz Nondestructive Stratigraphic Analysis of Complex Layered Structures: Reconstruction Techniques." Journal of Infrared, Millimeter, and Terahertz Waves (2021): 1-18.

for full paper see https://link.springer.com/article/10.1007/s10762-021-00819-1

Abstract

Terahertz (THz) time-of-flight tomography (TOFT), a nondestructive-evaluation technique for the stratigraphic characterization of structures with layers on the micron-to-millimeter scales, has proven to be challenging to apply to samples containing both micron-scale and millimeter-scale layers. In THz TOFT, echoes reflected from distant interfaces and defects are often obscured as they may be immersed in a noisy background as such features in the reflected signal may be weak due to attenuation and dispersion, leading to the loss of valuable information. Moreover, overlapping echoes from any optically thin layers, such as thin coatings on thick specimens, are likely to be mistaken for a single interface in reconstructing the stratigraphy. Thus, layered structures containing both thick and thin layers have proven problematic for THz TOFT characterization. In this paper, a sparse-deconvolution (SD) technique, based on an interior-point method, and including a propagation model accounting for dispersion is demonstrated. The method is shown to be successful in extracting the impulse response of samples that combine the challenges of both thick and thin layers. The robustness and effectiveness of this method are verified numerically and experimentally. While the proposed SD approach does not perform as well as cross-correlation (CC) techniques in terms of the maximum thickness, it can provide a clearer and more accurate reconstruction of moderately thick samples incorporating thin layers.

… It is noted that the bandwidth of the setup (TeraView Ltd. THz-TDS Spectra 3000) extends to 3 THz, corresponding to wavelength ~ 100 µm; however, in practice, accounting for the SNR of the reflected signal, the usable bandwidth in r(t) in these …

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Effective Medium Model Applied to Biopolymer Solutions

 Penkov, Nikita V., and Nadezda A. Penkova. "Effective Medium Model Applied to Biopolymer Solutions." Applied Spectroscopy (2021): 00037028211042027.

for full paper see https://journals.sagepub.com/doi/abs/10.1177/00037028211042027

Studying dielectric properties of heterogeneous systems is challenged by a problem of uncertainty of the ratio between dielectric permittivity of the system and dielectric permittivities of its components. Such ratios can be obtained in some cases using theoretical effective medium models. However, such models have not yet been developed for all the systems possible. Particularly, there is no effective medium model with filamentary inclusions. Such a theoretical model elaborated based on the fundamental principles of electrodynamics of continuous media is suggested in the present work. Any point of a filamentary inclusion with a length that is significantly greater than the thickness can be regarded as being located in a long cylinder-like fragment of the inclusion with stochastic direction of the cylinder axis relative to the external electric field. With this regard, electric field strength and electric induction values were averaged across the entire volume of a two-phase dielectric material. As a result, a model linking the dielectric permittivity of the two-phase system and the dielectric permittivities of both phases was elaborated. The model appears to be highly relevant for studying solutions of biopolymers, such as nucleic acids, fibrillar proteins and protein aggregates, polysaccharides, by means of electrical impedance spectroscopy, dielectric spectroscopy, and terahertz time-domain spectroscopy. The suggested theoretical model was successfully validated on a DNA solution within the terahertz region.

Optically Tunable Terahertz Metasurfaces Using Liquid Crystal Cells Coated with Photoalignment Layers

 Shih, Yi-Hong, Xin-Yu Lin, Harry Miyosi Silalahi, Chia-Rong Lee, and Chia-Yi Huang. "Optically Tunable Terahertz Metasurfaces Using Liquid Crystal Cells Coated with Photoalignment Layers." Crystals 11, no. 9 (2021): 1100.

for full paper see https://www.mdpi.com/2073-4352/11/9/1100

Abstract

An optically tunable terahertz filter was fabricated using a metasurface-imbedded liquid crystal (LC) cell with photoalignment layers in this work. The LC director in the cell is aligned by a pump beam and makes angles θ of 0, 30, 60 and 90° with respect to the gaps of the split-ring resonators (SRRs) of the metasurface under various polarized directions of the pump beam. Experimental results display that the resonance frequency of the metasurface in the cell increases with an increase in θ, and the cell has a frequency tuning region of 15 GHz. Simulated results reveal that the increase in the resonance frequency arises from the birefringence of the LC, and the LC has a birefringence of 0.13 in the terahertz region. The resonance frequency of the metasurface is shifted using the pump beam, so the metasurface-imbedded LC cell with the photoalignment layers is an optically tunable terahertz filter. The optically tunable terahertz filter is promising for applications in terahertz telecommunication, biosensing and terahertz imaging.

Experimental

A linearly polarized pump beam (center wavelength = 365 nm) was incident to the metasurface imbedded LC cell from the top substrate. The pump beam with an intensity of 0.3 mW/cm2  irradiated the photoalignment layers for 100 s, aligning the LC director in the cell. The LC director made angles θ of 0, 30, 60 and 90° with respect to the gaps of the SRRs of the metasurface by changing the polarized direction of the pump beam via a polarizer. The metasurface-imbedded LC cell was placed in the chamber of a terahertz spectrometer (TPS 3000, TeraView) for studying the effect of the polarized direction of the pump beam on the resonance frequency of the metasurface. Terahertz waves that were polarized in a direction parallel to the x axis of figure 1a were normally incident to this cell. TPS 3000 had a frequency resolution of 3 GHz in this work.

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Optical and electronic properties of iodine and bromine doped chirality enriched (12,1) and (13,2) single-walled carbon nanotubes

 

Abozied, Asmaa M., A. Abouelsayed, A. F. Hassan, A. A. Ramadan, Emad A. Al-Ashkar, and Badawi Anis. "Optical and electronic properties of iodine and bromine doped chirality enriched (12, 1) and (13, 2) single-walled carbon nanotubes." Carbon (2021).

for more information click here 

for full paper see https://www.sciencedirect.com/science/article/abs/pii/S0008622321009477

Abstract

We present transmission measurements on chirality enriched semiconducting (12,1) and (13,2) single-walled carbon nanotubes (CE-s-SWCNTs) and CE-s-SWCNTs doped with iodine (I2@CE-s-SWCNTs) and bromine (Br2@CE-s-SWCNTs) in wide frequency range from 0.1 to 40 THz. The real part of the optical conductivity σreal(ω) was fitted using Drude-Lorentz model. The Drude (D) term in the CE-s-SWCNTs was attributed to the presence of metallic tubes traces in the sample. The D/scattering rate(γD) ratio was increased by a factor of 1.13 and 2.35 with iodine and bromine p-doping, respectively. This increase was compensated by large increase in D term leading to an increase in the optical conductivity at the DC limit (σDC), growing from 186 Ω−1cm−1 for the CE-s-SWCNTs to 203 and 426 Ω−1cm−1 for the I2@CE-s-SWCNTs and Br2@CE-s-SWCNTs, respectively. In addition, the plasmon peak was shifted to higher frequencies and gains more spectral weight with doping. The calculated optical parameters determine that iodine and bromine create acceptor levels above the top of the CE-s-SWCNTs valence band by 0.04 and 0.08 eV, respectively, shifting the Fermi level. The high σDC value of the Br2@CE-s-SWCNTs is due to the higher electronegativity of bromine which enables removal of more electrons from the valence band of CE-s-SWCNTs to bromine acceptor levels.

Passively Tunable Terahertz Filters Using Liquid Crystal Cells Coated with Metamaterials

Chiang, Wei-Fan, Yu-Yun Lu, Yin-Pei Chen, Xin-Yu Lin, Tsong-Shin Lim, Jih-Hsin Liu, Chia-Rong Lee, and Chia-Yi Huang. "Passively tunable terahertz filters using liquid crystal cells coated with metamaterials." Coatings 11, no. 4 (2021): 381.

for full paper see https://www.mdpi.com/2079-6412/11/4/381/pdf

for more information click here

Abstract

Liquid crystal (LC) cells that are coated with metamaterials are fabricated in this work. The LC directors in the cells are aligned by rubbed polyimide layers, and make angles θ of 0◦ , 45◦ , and 90◦ with respect to the gaps of the split-ring resonators (SRRs) of the metamaterials. Experimental results display that the resonance frequencies of the metamaterials in these cells increase with an increase in θ, and the cells have a maximum frequency shifting region of 18 GHz. Simulated results reveal that the increase in the resonance frequencies arises from the birefringence of the LC, and the LC has a birefringence of 0.15 in the terahertz region. The resonance frequencies of the metamaterials are shifted by the rubbing directions of the polyimide layers, so the LC cells coated with the metamaterials are passively tunable terahertz filters. The passively tunable terahertz filters exhibit promising applications on terahertz communication, terahertz sensing, and terahertz imaging.


Experimental

.......Figure 2 displays the experimental terahertz spectra of three metamaterials that are coated with the PI layers. These spectra are obtained using a commercial terahertz spectrometer (TPS 3000, TeraView, Cambridge, UK) in transmission mode, and the chamber in the spectrometer is filled with nitrogen gas to prevent terahertz waves from absorbing moisture. The polarization of incident terahertz waves is set parallel to the x axis of Figure 1a. The PI-coated metamaterials have transmission peaks in their terahertz spectra due to the absorption of the electromagnetic resonance of the metamaterials. The transmission peaks are at an identical frequency of 0.588 THz, and the two PI-coated metamaterials .........

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A double layer FSS filter for sub-THz applications

 Ghavidel, A., M. Kokkonen, and S. Myllymäki. "A double layer FSS filter for sub-THz applications." Scientific Reports 11, no. 1 (2021): 1-8.

Abstract
This work presents the simulated and measured performance of single- and double-layer frequency selective surface filters for operation at sub-THz frequencies (250 GHz center frequency). They were composed of concentric square loops with a split as a unit cell resonator on top of a low dielectric permittivity, low thickness material (RT5880). Both a single layer filter and a cascaded two layer filter with varied distances were investigated. The simulated bandwidth for the cascaded filter was 27 GHz and 16 GHz and 9 GHz bandwidth measured with a THz-TDS and microwave system.

for full paper see https://www.nature.com/articles/s41598-021-99256-2

for more information click here

Measurement using THz time-domain spectroscopy

A TeraPulse system (TeraPulse 4000, TeraView UK,  Fig. 7a, was used to measure the FSS filter’s impact on time-delay and transmittance and the results are shown in Fig. 7b,c. The single layer FSS filter was placed between two mirrors and the thickness of the FSS created a time-delay (around 0.1 picosecond) and reduced the amplitude to 0.9 compared to the reference signal amplitude (12.5). With a second layer, the time-delay increased to 0.5 ps and reduced the transmittance amplitude to 0.43. It was observed that each layer reduced the transmitted wave amplitude by around 30%. The bandwidth was measured to be ~ 12 GHz with one layer and ~ 16 GHz with two layers at 95% transmittance level.

Figure 7

(a) TeraPulse 4000 Spectroscopy system for measuring FSS filter, measured and normalized (b) measured pulse response of electric field amplitude where the refence signal was measured without the FSS layer and (c) measured signal transmittance of single- and double-layer unit cell.

Terahertz spectroscopic analysis of non-radiated and radiated synthetic and natural polymer/GO nanocomposites

Mohamed, F., R. A. Zaghlool, and W. El Hotaby. "Terahertz spectroscopic analysis of non-radiated and radiated synthetic and natural polymer/GO nanocomposites." Journal of Molecular Structure (2021): 131659.

Abstract

Absorption coefficient, refractive index, and dielectric parameters of two sets of polymers: synthetic polymers (poly acrylamide, and poly vinyl alcohol), and natural polymers (chitosan, and cellulose acetate) have been investigated using Terahertz time-domain spectroscopy THz-TDS in the frequency range of 0.3 THz - 3.0 THz. It is found that these parameters are significantly boosted by the presence of graphene oxide (GO) as a filler. The influence of electron beam radiation of a dose of 50 kGy on the absorption coefficient, and refractive index is also investigated. An observable decrease in these parameters is illustrated in the un-doped and doped membranes upon irradiation. By this study, we shed light on how the THz-TDS is able to identify any variant change in the structure due to incorporation of GO or as an influence of electron beam radiation.

… atmosphere. 2.2.4. THz time- domain spectroscopy (THz-TDS). The terahertz spectrometer in the frequency range of 0.3 THz and 3 THz (10 cm −1 -100 cm −1 ), TPS spectra 3000 system, TeraView Ltd England, was used. To … 

 for more information click here

Study of Thin hBN /WS2 Films by Terahertz Time Domain Spectroscopy

 Oparin, E. N., M. O. Zhukova, V. G. Bulgakova, S. A. Pozdnyakova, and A. N. Tcypkin. "Study of Thin hBN/WS2 Films by Terahertz Time-Domain Spectroscopy."

Abstract 

Estimates of the linear optical properties of promising material for the THz modulators manufacture, i. e., thin films of the mixture of tungsten disulfide and boron nitride with hexagonal lattice on polyethylene terephthalate (PET) substrate in the broadband terahertz frequency range are presented in this paper. In the range from 0.5 to 2.5 THz the films showed high transparency exceeding 90%. The calculated refractive index value 1.75 exceeded the ones for TPX and PET – materials used in the manufacture of THz optics.

for full paper see https://www.photonics.su/files/article_pdf/8/article_8237_682.pdf

..........The studies were carried out using a laboratory setup of THz time-domain spectroscopy of TeraPulse 4000 manufactured by TeraView, shown in Fig. 1. In this system, a photoconductive antenna illuminated by the radiation of a femtosecond (fs) fiber laser is used......

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Understanding the Metastability of Theophylline FIII by Means of Low-Frequency Vibrational Spectroscopy

 Paiva, Eduardo Maia, Qi Li, Adam J. Zaczek, Claudete F. Pereira, Jarbas José Rodrigues Rohwedder, and J. Axel Zeitler. "Understanding the Metastability of Theophylline FIII by Means of Low-Frequency Vibrational Spectroscopy." Molecular Pharmaceutics (2021).

Abstract
While theophylline has been extensively studied with multiple polymorphs discovered, there is still currently no conclusive structure for the metastable theophylline form III. In this present work, by combining more widely used techniques such as X-ray diffraction and thermogravimetric analysis with more emerging techniques like low-frequency Raman and terahertz time-domain spectroscopy, to analyze the structure and dynamics of a crystalline system, it was possible to provide further evidence that the form III structure has a theophylline monohydrate structure with the water molecules removed. Solid-state density functional theory simulations were paramount in proving that this proposed structure is correct and explain how vibrational modes within the crystal structures feature and govern polymorphic transitions and the metastable form III. Through the insight provided by both simulated and experimental results, it was possible to decisively conclude the elusive crystal structure of theophylline form III. It was also shown that the correct space group for theophylline monohydrate is not P21/n but, in fact, Pc.

for full paper see https://pubs.acs.org/doi/full/10.1021/acs.molpharmaceut.1c0047

.......THz-TDS experiments were used to track the entire dehydration process of FM by placing the sample pellet under vacuum or by purging the sample chamber that contained the sample with a dry nitrogen gas overnight, both of which achieved the same results. In these cases, the terahertz transmission spectra were acquired with the TeraPulse 4000 spectrometer (TeraView Ltd.) at a continuous measurement interval of 10 s per spectrum for measurements acquired during a dehydration under vacuum and 5 min.....

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Terahertz-infrared dielectric properties of lead-aluminum double-cation substituted single-crystalline barium hexaferrite

 Ahmed, Asmaa, Anatoly S. Prokhorov, Vladimir Anzin, Denis Vinnik, Sergei Ivanov, Adam Stash, Y. S. Chen, Alexander Bush, Boris Gorshunov, and Liudmila Alyabyeva. "Terahertz-infrared dielectric properties of lead-aluminum double-cation substituted single-crystalline barium hexaferrite." arXiv preprint arXiv:2108.08571 (2021).

Abstract 

Hexaferrite materials are highly demanded to develop and manufacture electronic devices operating at radio- and microwave frequencies. In the light of the prospects for their use in the forthcoming terahertz electronics, here, we present our results on the terahertz and infrared dielectric response of a typical representative of hexaferrites family, lead-substituted M-type barium hexaferrite doped with aluminum, Ba0.2Pb0.8AlxFe12-xO19, x(Al)=0.0, 3.0, and 3.3. We studied uniquely large and high-quality single crystals of the compounds prepared by spontaneous crystallization growth technique. Our aim was to explore the effect of aluminum substitution on the dielectric response of the compounds. Systematic and detailed investigations of the dependences of terahertz-infrared (frequencies 8 - 8000 cm-1 ) spectra of complex dielectric permittivity on the temperature, 4 - 300 K, and on the chemical composition, x(Al)=0.0, 1.2, 3.0, 3.3, were performed for two principal polarizations of the electric field E-vector of the probing radiation relative to the crystallographic c-axis, namely E||c and Ec. Furthermore, infrared phonon resonances are recorded and discussed. In contrast to undoped BaFe12O19, no softening of the lowest frequency A2u phonon is observed, indicating suppression of a displacive phase transition in substituted compounds. A number of resonance absorption bands are discovered at terahertz frequencies and assigned to transitions between energy levels of the fine-structured ground state of Fe2+ ( 5 E) ions. The temperature and aluminum-doping dependences of the resonances are analyzed with an account taken of disorder introduced by aluminum. Basing on dielectric data and detailed X-ray experiments, we find that for all concentrations of Al3+ ions, x(Al)=0.0, 1.2, 3.0, and 3.3, they mainly occupy the 2a and 12k octahedral site positions and that the degree of substitution of iron in tetrahedral positions is not substantial. Along with fundamental findings, the obtained data on broad-band dielectric properties of Ba0.2Pb0.8AlxFe12-xO19 crystals provides the information that can be used for development and manufacture of electronic devices with operating frequencies lying in the terahertz spectral band. Keywords M-type hexaferrite, multiferroics, dielectric properties, site occupancy of Al in BaM, Fourier transform infrared spectroscopy, terahertz time-domain spectroscopy.

for full paper see https://arxiv.org/ftp/arxiv/papers/2108/2108.08571.pdf

Visualising liquid transport through coated pharmaceutical tablets using terahertz pulsed imaging

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In-situ Observation of the Structure of Crystallising Magnesium Sulfate by Terahertz Spectroscopy

 

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How does the tableting process affect the quality of pharmaceutical tablets?

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