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 …

for more information about TeraView click here.

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.

for more information about TeraView and its products click here.