Terahertz radiation in ophthalmology (review)

Terahertz (THz) radiation is one of the new, intensively studied interdisciplinary fi elds of scientifi c knowledge, including medicine, in the fi rst decades of the 21st century. At the beginning of this article (review), in a brief form, the basic statements on THz radiation, the main parameters and properties are presented; the modern THz biophtonics technologies used in biology and medicine are considered – THz refl ectometry, THz spectroscopy methods. Then a number of directions and examples of possible use of THz technologies in biology and medicine, including pharmaceuticals, are given. The main part of the review presents the progress of experimental research and the prospects for the clinical application of medical technologies of THz spectroscopy, THz imaging, in ophthalmology in the study of the morphological and functional state of the ocular surface structures, diagnosis, medical testing, and treatment of ophthalmopathology of the ocular surface. The article concludes with a review of experimental studies on the safety of using THz waves for medical diagnostics and treatment of ophthalmopathology. In the fi nal part, the main problems and prospects of introducing medical THz technologies into the clinical practice of an ophthalmologist are considered.

Tunable polarization comb based on the electromagnetically induced transparency with hybrid metal-graphene metamaterial

Noted a linear-to-circular polarization comb based on electromagnetically induced transparency (EIT) with hybrid metal-graphene metamaterial in terahertz (THz) spectroscopy. Due to the near field coupling between the bright mode of metal cut-wire (MCW) and multiple dark modes, the multi-peak EIT effect is exhibited under the x-polarized incidence supported by the three-level theory. With another orthogonal MCW etched on the back of the SiO2, the asymmetry responses in both polarized incidences (x- and y-polarized waves) further triggers the linear-to-circular polarization conversion (LTCPC). The values of four corresponding circular-polarized frequencies combined with transmission coefficients respectively are 0.90 THz with 0.45, 1.02 THz with 0.64, 1.15 THz with 0.60, 1.32 THz with 0.53, confirmed via relevant axial ratios and the electric field distributions. On the other hand, the drastic phase changes in transparent windows raise high group delays, among which the maximum value approaches 325 ps. Additionally, DC-voltage-driven graphene strips are doped at both ends of the back MCW to enhance the reconfigurability, superior tunable transmission behaviors illuminated by y-polarization with obvious changes at 0.90 THz and 1.02 THz can be achieved with the dynamic Fermi level fluctuating between 0.01 eV and 0.8 eV. Such an implementation creates a novel path to polarization modulators, signal transceivers, and information transmission devices.

Recent advances in THz detectors based on semiconductor structures with quantum confinement: a review

Beginning from the 1990s, an ever-lasting interest in the THz spectroscopy and THz instruments has produced wide progress in the development of high-speed THz detectors. The constantly growing requirements aimed at the increase of spectral resolution, sensitivity, and acquisition rate of THz detectors have attracted much attention in this field till nowadays. In the present review, we summarize the most recent advances in the THz photodetectors based on semiconductor structures with quantum confinement of an electron gas. Their main advantages over existing detectors are fast response time, increased spectral resolution, and multicolor operation thanks to the variability of their designs and band structure engineering. These all allow using them in various important applications as single photon detection, THz heterodyne detection, continuous monitoring of toxic gases, THz free space communications, and radio astronomy, as well.

Integrative chemo-immune-radiological treatment of HER2 positive breast cancer combined with a review of potential microRNAs involved and analysis of experimental results from sub-THz vibrational spectroscopy

In this paper we present the results of a Breast Cancer study by integrative analysis of a NIH approved treatment for HER2 positive breast cancer. This study is combined with analysis of Micro-RNA involvement from application of sub-THz spectroscopy for visualization of molecules circulating in blood by measuring saliva. The combination of Taxol-Generic Name-Paclitaxel (PT-J9267) and Trastuzumab-ANNS 0/0 and KadcylaTM (Genetic Name Ado-Trastuzumab Emtansine) were used in 3-stages of combined chemotherapeutic and immune-treatments followed by Radiation treatment. The goal of using PT was to stop spread of the disease to other organs outside of the breast and under arm lymph nodes, as well as to shrink the size of the tumor to facilitate surgery and radiology in continuation of the treatment. Trastuzumab (TZ) was added to PT in the 2nd step to prevent the development of chemoresistance. Intravenous infusion of Kadcyla was used mainly to prevent metastasis. Integrative analysis of microRNA participation was conducted based on literature review and sub-Terahertz vibrational spectroscopy measurements of absorption spectra from samples taken weekly before and after each treatment, using Vibratess’ spectrometer. The results from sub-THz spectroscopy in this work demonstrate dramatical modification of spectroscopic signatures from patient samples following disease development and the initial steps in the course of treatment. These changes reflect the deep global regulation (reduction) of the initially participating microRNAs amounts and changes in the microRNAs contributing to the spectra.

Accurate THz Ellipsometry Using Calibration in Time Domain

We report on the realisation of a customized THz Time Domain Spectroscopic Ellipsometer (THz-TDSE) based on fiber-coupled photoconductive antennas, operating in a wide range of incident angles and allowing also standard transmission spectroscopy without any optical realignment. To ensure accurate parameter extraction for a broad range of materials, we developed a fast and effective algorithm-assisted method to calibrate the setup and compensate for the nonideality in the response of the THz system. The procedure allows to minimise errors induced by imperfect response of the antennas and polarizers, imprecise setting of the impinging and receiving angles in the goniometric mechanical arms, and unavoidable mismatches in the THz beam optics. Differently from other calibration methods applied in the literature, our approach compares in time domain the ellipsometric derived electric field s- and p-polarised components at a given angle of incidence with the reconstructed ones, attained by using the complex dielectric function of a known sample. The calibrated response is determined with high precision by setting the system in transmission mode. In order to validate the technique, ellipsometric measurements have been carried out at various angle of incidences on a number of materials both in solid and liquid form, and their data compared with what obtained by conventional THz spectroscopy. Results show that THz-TDSE accompanied with an accurate calibration procedure is an effective technique for material characterization, especially in case of samples with a high absorption rate that are not easily investigated through transmission measurements.

Monitoring the Effect of Transdermal Drug Delivery Patches on the Skin Using Terahertz Sensing

Water content of the skin is an important parameter for controlling the penetration rate of chemicals through the skin barrier; therefore, for transdermal patches designed for drug delivery to be successful, the effects of the patches on the water content of the skin must be understood. Terahertz (THz) spectroscopy is a technique which is being increasingly investigated for biomedical applications due to its high sensitivity to water content and non-ionizing nature. In this study, we used THz measurements of the skin (in vivo) to observe the effect of partially and fully occlusive skin patches on the THz response of the skin after the patches had been applied for 24 h. We were able to observe an increase in the water content of the skin following the application of the patches and to identify that the skin remained hyper-hydrated for four hours after the removal of the fully occlusive patches. Herein, we show that THz spectroscopy has potential for increasing the understanding of how transdermal patches affect the skin, how long the skin takes to recover following patch removal, and what implications these factors might have for how transdermal drug patches are designed and used.

MULTICHARME: A modified Chernin-type multi-pass cell designed for IR and THz long-path absorption measurements in the CHARME atmospheric simulation chamber

We have developed MULTICHARME, a modified Chernin-type multi-pass cell especially designed for IR and THz long-path absorption measurements in the CHamber for Atmospheric Reactivity and Metrology of the Environment (CHARME). By measuring the output power using a near-IR diode-laser and a THz amplified multiplication chain, we have established that the effective reflectivity of MULTICHARME is better than 94 % over approximately three decades of frequency. Absorption measurements of N2O have been performed by probing highly excited rovibrational transitions in the near-IR and ground state rotational transitions at submillimetre wavelengths. In each case the linearity of the absorbance with the pathlengths was verified. Finally, we demonstrate that THz spectroscopy is able to study the isotopic composition of greenhouse polar gases such as N2O and to absolutely quantify stable (N2O) and reactive (O3) species at trace levels. Moreover, a THz monitoring at low pressure of the ozone decay in the chamber has been performed. The deduced ozone lifetime of 3.4 ± 0.1 h is shorter compared with previous measurements performed in CHARME at atmospheric pressure. For the first time, the ability of THz rotational spectroscopy to monitor, with a very high degree of selectivity, stable and reactive polar compounds at trace level in an atmospheric simulation chamber is demonstrated. However, the sensitivity of the THz monitoring needs to be improved to reach the atmospheric trace levels. For this purpose, it is necessary to figure out the baseline variations as well as possible induced by the multiple standing waves present in MULTICHARME.

Diffuse Terahertz Spectroscopy in Turbid Media Using a Wavelet-Based Bimodality Spectral Analysis

Current terahertz (THz) spectroscopy techniques only use the coherent light beam for spectral imaging. In the presence of electromagnetic scattering, however, the scattering-mitigated incoherent beams allow for flexible emitter-detector geometries, which enable applications such as seeing through turbid media. Despite this potential, THz spectroscopy using diffuse waves has not been demonstrated. The main obstacles are the very poor signal to noise ratios of the diffused fields and the resonance-like spectral artifacts due to multiple Mie scattering events that obscure the material absorption signatures. In this work, we demonstrate diffuse THz spectroscopy of a heterogeneous sample through turbid media using a novel technique based on the wavelet multiresolution analysis and the bimodality coefficient spectrum, which we define here for the first time using the skewness and kurtosis of the spectral images. The proposed method yields broadband and simultaneous material characterization at detection angles as high as 90o with respect to the incident beam. We determined the accuracy of the wavelet-based diffuse spectroscopy at oblique detection angles, by evaluating the area under the Receiver Operating Characteristic (ROC) curves, to be higher than 95%. This technique is agnostic to any a priori information on the spectral signatures of the sample materials or the characteristics of the scattering medium, and can be expanded for other broadband spectroscopic modalities.

Diffuse terahertz spectroscopy in turbid media using a wavelet-based bimodality spectral analysis

Current terahertz (THz) spectroscopy techniques only use the coherent light beam for spectral imaging. In the presence of electromagnetic scattering, however, the scattering-mitigated incoherent beams allow for flexible emitter-detector geometries, which enable applications such as seeing through turbid media. Despite this potential, THz spectroscopy using diffuse waves has not been demonstrated. The main obstacles are the very poor signal to noise ratios of the diffused fields and the resonance-like spectral artifacts due to multiple Mie scattering events that obscure the material absorption signatures. In this work, we demonstrate diffuse THz spectroscopy of a heterogeneous sample through turbid media using a novel technique based on the wavelet multiresolution analysis and the bimodality coefficient spectrum, which we define here for the first time using the skewness and kurtosis of the spectral images. The proposed method yields broadband and simultaneous material characterization at detection angles as high as 90° with respect to the incident beam. We determined the accuracy of the wavelet-based diffuse spectroscopy at oblique detection angles, by evaluating the area under the receiver operating characteristic curves, to be higher than 95%. This technique is agnostic to any a priori information on the spectral signatures of the sample materials or the characteristics of the scattering medium, and can be expanded for other broadband spectroscopic modalities.