A novel highly sensitive porous core-photonic crystal fiber (PC-PCF) has been designed and analyzed for detection of chemical analytes in the terahertz frequency range. The PC-PCF is designed using rectangular structured air holes in the core with a kagome structured cladding. The full vectorial finite-element method is used to tune the geometrical parameters and to characterize the fiber. Our results demonstrate a high relative chemical sensitivity with significantly lower confinement loss for different analytes. Moreover, the PCF shows near zero dispersion variation, high modal effective area, high birefringence, and high numerical aperture. The practical realization of the fiber is feasible with present fabrication techniques. Our optimized PCF has commercial applications in chemical sensing as well as applications in terahertz systems that require guided polarization preserving transmission.

A Novel Approach for Spectroscopic Chemical Identification Using Photonic Crystal Fiber in the Terahertz Regime

Terahertz biophotonics as a tool for studies of dielectric and spectral properties of biological tissues and liquids

Quality control and authentication of packaged integrated circuits using enhanced-spatial-resolution terahertz time-domain spectroscopy and imaging

Over the past decades, signicant attention has been paid to biomedical applications of terahertz (THz) technology. Nowadays, THz spectroscopy and imaging allow for solving numerous demanding problems in biological, medical, food, plant and pharmaceutical sciences. Among all biomedical applications, a label-free diagnosis of malignant and benign neoplasms represents one of the most attractive branches of THz technology. Despite the attractiveness, the methods of THz diagnosis are still far from medical practice. In this review, we consider the modern research results in THz diagnosis of malignant and benign neoplasms, along with the topical research and engineering problems, which restrain the THz technology translation to clinics. We start from analysis of the common models of THz-wave { tissue interactions and the eects of tissue exposure to THz waves. Then, we discuss existing modalities of THz spectroscopic and imaging systems, which either have been already applied in medical imaging, or hold strong potential. We summarize the earlier-reported and the original results of THz measurements of neoplasms with dierent nosology and localization. We pay attention to the origin of contrast between healthy and pathological tissues in the THz spectra and images and discuss the prospective of THz technology in non-invasive, minimally-invasive and intraoperative diagnosis, as well as in aiding histology. Finally, we review the challenging problems of THz diagnosis, as well as attempts to solve them, which should bring the THz technology much closer to the medical practice. This review allows one to objectively uncover benets and weaknesses of the THz technology in diagnosis of malignant and benign neoplasms.

https://iopscience.iop.org/article/10.1088/2040-8986/ab4dc3/pdf

The progress and perspectives of terahertz technology for diagnosis of neoplasms: a review

In recent years, biopolymers are getting wide attention with the perspective of developing high-performance biocomposites with low environmental impact owing to their unique and useful features such as abundant availability, renewability, ecofriendliness and lightweight. Biopolymer composites are expected to replace many conventional materials in optical, biological, and engineering applications as the investment and research on these materials increase substantially. The desired properties of biopolymer composites can be achieved by blending an appropriate biopolymer with suitable additives, which pave the way for polymer-filler interaction. A variety of parameters such as chemical composition, degradation kinetics and mechanical properties of biopolymer composites can be tailored according to the application needs. The interfacial interactions between the biopolymer and the nanofiller have a significant effect on the mechanical properties of biopolymer composites. The present review is focused on the recent advances in the mechanical properties of various biopolymer composites. In the first part of this review, the unfamiliar mechanical characterization techniques such as fatigue test, nanoindentation and nondestructive testing of biopolymer composites have been discussed. In the later part, the various popular processing techniques of biocomposite fabrication have been discussed. In addition, in the conclusion section, few challenges associated with the processing and mechanical performance of biopolymer composites have been described

Recent advances in mechanical properties of biopolymer composites: a review

Reconstructing the dielectric permittivity profile (depth dependence of sample dielectric permittivity) is an important inverse problem. We present a new method for permittivity profile reconstruction based on terahertz time-domain spectroscopy signal processing. Reconstruction is accomplished in two steps. First, the sample pulse function is reconstructed using sample time-domain reflection data. Low- and high-frequency noise filtering and the interpolation of the pulse function at low frequencies are then applied. Second, an invariant embedding technique is used to calculate the dielectric permittivity profile based on the sample pulse function. Samples with known permittivity profiles have been studied experimentally using this procedure in order to verify this algorithm. This algorithm is stable to additive Gaussian white noise as shown using mathematical modeling based on the finite-difference time-domain technique. Possible applications of this permittivity profile reconstruction technique are discussed.

https://www.spiedigitallibrary.org/journals/optical-engineering/volume-52/issue-6/068203/Invariant-embedding-technique-for-medium-permittivity-profile-reconstruction-using-terahertz/10.1117/1.OE.52.6.068203.pdf

Invariant embedding technique for medium permittivity profile reconstruction using terahertz time-domain spectroscopy

The paper contains recent results of studying the ability of human body disease diagnosis with terahertz time-domain spectroscopy. In vitro skin cancer samples (squamous cell carcinoma, epithelioid cell melanoma, infiltrating carcinoma) were studied experimentally with terahertz pulsed spectrometer. The parametrical in vitro images of skin cancers are presented. The ability to make early tooth cariosity diagnosis with terahertz time-domain spectroscopy was also shown experimentally. The results of studying the in vitro tooth samples are presented and discussed.

http://iopscience.iop.org/article/10.1088/1742-6596/486/1/012014/pdf

Medical diagnostics using terahertz pulsed spectroscopy

This paper shows an ability to find internal defects in construction of polymer composite material using THz imaging. Using THz vision system resulted in an example of finding internal non-impregnated area in fiberglass.

https://iopscience.iop.org/article/10.1088/1742-6596/486/1/012008/pdf

Nondestructive testing of polymer composite materials using THz radiation

Terahertz (THz) imaging is a relatively new field of optical engineering and physics. Despite it has been already used in such directions as biomedical imaging, non-destructive evaluation of materials, and security detection of concealed objects, there are many problems in the development of them, connected with low efficiency of imaging sources and detectors. A new type of THz imaging system was implemented, based on backward wave oscillator THz source. Its efficiency of detecting concealed objects was shown.

BWO based THz imaging system

Scattering of THz radiation in inhomogeneous media is an important reason of reducing spectral information in received THz signal for different applications. Scattering of THz radiation in thin layers of dielectric material was studied, particularly, in fabric materials. A structure of different types of cloth fabric was studied, and mathematical model of fabric was suggested, which is a system of dielectric cylinders. Scattering of THz radiation was modeled numerically. Scattering cross-section and indicatrix were calculated, and then spectral transmittance was computed. During a set of experiments THz spectral transmittance of various fabric materials were obtained and numerical results were approved. The developed method for receiving scattering characteristics of different materials can be used for extracting useful information from received THz signal.

Irina N. Fokina

Papers

Invariant embedding technique for medium permittivity profile reconstruction using terahertz time-domain spectroscopy

Medical diagnostics using terahertz pulsed spectroscopy

Nondestructive testing of polymer composite materials using THz radiation

BWO based THz imaging system

Scattering of terahertz radiation in thin layers of dielectric materials