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In this paper, we propose a computational approach for description of radiation transfer in a quasi-ordered medium and study the impact of scattering on electromagnetic wave propagation and image formation. It combines finite-difference time-domain method, Monte Carlo simulations, and radiative transfer theory. Using, as an example, terahertz (THz) imaging, we analyze the modulation transfer function (MTF) of the imaging system operated at 0.25 THz for scattering material layers placed between the object and the imaging plane. We experimentally study imaging of bar-pattern test objects through a quasi-ordered scattering medium. Both numerical and experimental results are in good agreement and demonstrate an impact of quasi-ordered scatterers on quality of THz images, i.e., particular combination of the electromagnetic wavelength and parameters of scattering materials could enhance MTF compared with ones with random particle structures.

A method for phase identification (MPI) in two-dimensional (2D) condensable systems is proposed on the basis of the analysis of the Voronoi cells’ characteristics. A simple algorithm is developed for determination of particles belonging to a condensate, a gaseous state, and an interface between them (“surface”). The efficiency and stability of the developed method is studied using molecular dynamics simulations and calculation of binodals in 2D systems with both short- and long-range attraction between particles. To illustrate prospectives of the method for experimental studies, 2D clusters of 2.12 µm diameter colloidal silica particles assembled in a rotating external electric field have been analyzed using the MPI. The results prove that the MPI possesses high accuracy and can be applied to analyze in detail both simulation data (obtained by molecular dynamics or Monte Carlo methods) and results of particle-resolved experimental studies (with colloidal suspensions and complex (dusty) plasmas) of solids and liquids when the considered multiparticle systems can undergo spinodal decomposition. The developed method can be generalized to analyze three-dimensional and multicomponent systems, and therefore, the presented results are of relevance for a broad range of problems in physical chemistry, chemical physics, and materials science.

In this paper, an ability for highly efficient terahertz (THz) waveguiding in multichannel sapphire shaped crystals is demonstrated. The edge-defined film-fed growth (EFG) technique (or Stepanov technique) of shaped crystal growth has been implemented to manufacture the THz photonic crystalline (PC) waveguide. The PC waveguide has been characterized using both numerical simulations and experimental study. It allows guiding the THz waves in multimode regime with the minimal dispersion in frequency range of $1.0$ –$1.55$ THz and the minimal power extinction coefficient of $0.02$ dB $/$cm at $1.45$ THz. The mode interference phenomenon has been observed in this waveguide highlighting the prospectives of its use for intrawaveguide interferometry. These results demonstrate the capabilities of combining the EFG/Stepanov technique advantages with unique properties of sapphire, such as relatively low THz-wave absorption, high mechanical, thermal, chemical, and radiation strength, for manufacturing the THz waveguides characterized with low loss and dispersion and suitable for use in wide range of THz technology applications in biomedical and material sciences, including sensing in aggressive environment.

A method to reconstruct the terahertz (THz) refractive index and absorption coefficient of in vivo tissue using THz pulsed spectroscopy (TPS) has been proposed. The method utilizes a reference THz window to fix the sample of interest during the TPS reflection mode measurements. Satellite pulses caused by multiple THz-wave reflections in the reference window are taken into account to accurately solve the inverse problem. The stability of the proposed method in the presence of various factors, including digital noise in the TPS waveforms and fluctuations of the reference THz window position, has been accurately analyzed. The method has been implemented to study in vivo the THz refractive index and absorption coefficient of the human skin. The skin from three persons has been measured, and the results agree with the well-known data on healthy skin spectroscopy in general, except for several regions of the skin. Thus, for the elbow, the hand, the knee, and the heel the THz refractive index and absorption coefficient considerably differ from the average values. The observed results are of principle importance for further development of novel approaches to skin diagnosis based on THz technologies.

Nowadays, composite materials are widely used in building and construction industry, in motor-vehicles, spacecrafts and aircrafts, and in biomedical science due to the ability of combining various consistent components for manufacturing composite materials with physical and chemical properties significantly different from the properties of each component. Polymer composite materials (PCMs) appear to be the most common type of composites. PCMs consist mainly of polymer binder reinforced with the glass-fiber-fabric. Although PCMs are widely applied, PCM manufacturing technology lacks the methods of non- destructive testing. In this paper we demonstrate that terahertz (THz) pulsed spectroscopy (TPS) appears to be a unique instrument for solving important problems of PCM manufacturing control. We experimentally demonstrate the efficiency of TPS for non-destructive control of PCM binder polymerization, since THz radiation is sensitive to changes of picosecond dynamics in media. Furthermore, we show the ability to detect the internal non-impregnated voids inside the PCM structure by means of THz time-of-flight tomography. These results highlight the potentials of TPS applications for non-destructive control of PCM manufacturing process.