Transmission and reflection spectra of single-crystal germanium plates were experimentally measured in the terahertz spectral range. The optical parameters of germanium were determined at various Sb-doping levels. Saturation of the absorption index was detected with increasing wavelength in the range of 1000–3000 μm. The optical parameters of germanium correspond to the Drude-Lorentz model.

For the first time, in a single experiment, the dependence of the position of the phonon absorption peaks in the IR spectrum (range 11–40 μm) for all five stable monoisotopic germanium single crystals was studied. The dependence obtained can be used to study the mass composition of germanium of various isotopic purity.

Reflectivity and transmittance of conductive films of indium tin oxide (ITO) deposited on a borosilicate glass substrate were experimentally investigated. Measured spectra were numerically analyzed using the transfer matrix method under consideration of high-frequency electron conductivity of the film via a Drude model. A non-destructive method for determining the film parameters has been developed. A correlation has been found between the microwave shielding effectiveness of the ITO coating and its near-infrared reflectivity.

Представлена современная приборная база и методики измерений оптически прозрачных материалов в широком спектральном диапазоне – ​от ультрафиолетового до терагерцевого. Особое внимание уделено терагерцевому диапазону – ​сравнительно новому направлению оптики, находящемуся на стыке с радиофизикой.

Purpose: The terahertz (THz) medical imaging is a promising noninvasive technique for monitoring the skin's conditions, early detection of the human skin cancer, and recovery from burns and wounds. It can be applied for visualization of healing process directly through clinical dressings and restorative ointments, minimizing the frequency of dressing changes. The THz imaging technique is cost effective, as compared to the magnetic resonance method. Our aim was to develop an approach capable of providing better image resolution than the commercially available THz imaging cameras. Approach: The terahertz-to-infrared (THz-to-IR) converters can visualize the human skin cancer by converting the latter's specific contrast patterns recognizable in THz radiation range into IR patterns, detectable by a standard IR imaging camera. At the core of suggested THz-to-IR converters are flat matrices transparent both in the THz range to be visualized and in the operating range of the IR camera; these matrices contain embedded metal nanoparticles, which, when irradiated with THz rays, convert the energy of THz photons into heat and become nanosources of IR radiation detectable by an IR camera. Results: The ways of creating the simplest converter, as well as a more complex converter with wider capabilities, are considered. The first converter is a gelatin matrix with gold 8.5 nm diameter nanoparticles, the second is a polystyrene matrix with 2 nm diameter nanoparticles from copper-nickel MONEL (c) alloy 404. Conclusions: An approach with a THz-to-IR converter equipped with an IR camera is promising in that it could provide a better image of oncological pathology than the commercially available THz imaging cameras do.

A clear correspondence between the position of the peak in the IR absorption spectrum of isotopically pure germanium single crystals and the mass number of the isotope was found. The dependence obtained can be used for express analysis of the mass composition of isotopically pure germanium single crystals.

This work reports the effect of tin (Sn) doping on the infrared (IR) and terahertz (THz) properties of vanadium dioxide (VO2) films. The films were grown by hydrothermal synthesis with a post-annealing process and then fully characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and temperature-controlled electrical resistivity as well as IR and THz spectroscopy techniques. Utilizing (NH4)(2)SnF6 as a Sn precursor allows the preparation of homogeneous Sn-doped VO2 films. Doping of VO2 films with Sn led to an increase in the thermal hysteresis width while conserving the high modulation depth in the mid-IR regime, which would be beneficial for the applications of VO2 films in IR memory devices. A further analysis shows that Sn doping of VO2 films significantly affects the temperature-dependent THz optical properties, in particular leading to the suppression of the temperature-driven THz transmission modulation. These results indicate Sn-doped VO2 films as a promising material for the development of switchable IR/THz dichroic components.

We report on the experimental studies of the interaction of electromagnetic radiation with borosilicate crown glass K108 in the ultrawide frequency range from 0.002 to 1500 THz. Four different types of spectrometers are used to measure the reflectivity and/or transmittance spectra. Spectral dependences of the complex dielectric permittivity, refractive index and extinction coefficient are extracted from the measured spectra. The optical properties of the borosilicate crown glass in the microwave spectral range (2–23 GHz) are investigated for the first time. There are three bands of anomalous dispersion in the spectral curve of the real part of the dielectric permittivity. Each band of the anomalous dispersion corresponds to an absorption band, which is clearly seen in the spectrum of the imaginary part of the dielectric permittivity. The wide low-frequency absorption band is attributed to the Boson peak. Two other examined absorption bands represent sharp peaks and are associated with the Si–O–Si bending and Si–O stretching vibration modes. The results of the study can be useful in the development of optics based on the borosilicate crown glass.

The design, manufacture and study by methods of spectroscopy and microscopy of terahertz metal-dielectric photonic quasicrystal structures are considered.

The transmission in the terahertz spectral range of crystalline fluorides of Lithium (LiF), Calcium (CaF2), Barium (BaF2) and Magnesium (MgF2), which are widely used in ultraviolet and infrared spectral optics, was studied. The spectral dependences of the absorption coefficient of these materials were obtained, in the region of 200-3000 mu m a transparency zone was registered. This is of interest for the possible use of fluorides in THz devices in the millimeter range.

Spectral dependences of the transmittance of CsI, AgCl, KRS-5 (TlBr–TlI), and KRS-6 (TlCl–TlBr) single crystals in the infrared (IR) and terahertz (THz) spectral ranges are measured. Spectral dependences of the absorption (attenuation) coefficient of these crystals in the spectral range of 200–3000 μm are calculated. It is found that these crystals are transparent in the millimeter range, which makes it possible to use them in THz devices. It should be noted that, in contrast to the IR spectral range, the optical quality of the surface of crystal samples barely affects the transmittance in the millimeter range.

Prospects for the development of devices for visualizing terahertz (THz) radiation sources can be associated with the use of the results of old studies (1965–1978) on the absorption of THz radiation by metal nanoparticles. This “renaissance” demonstrates that metallic nanoparticles can be used as nanotransducers of invisible THz radiation to infrared (IR) radiation detectable by a commercial IR camera. The investigated THz-to-IR converters are matrices that are transparent both in the THz radiation range to be visualized and in the operating range of the IR camera; matrices contain embedded metal nanoparticles. The latter, when irradiated with THz rays, convert the energy of THz photons into heat and become nanosources of IR radiation for the IR camera. In metal nanoparticles, the mechanisms of absorption of THz radiation and its conversion into heat are realized through dissipation of the energy of THz photons due to multiple scattering of electrons, as well as because of excitation of two types of phonons (transverse and longitudinal ones). The conversion of THz energy into the energy of transverse phonons occurs directly, while dissipation and excitation of longitudinal phonons occurs indirectly, through the excitation of Fermi electrons. Polyvinylchloride (PVC) was chosen as the matrix material, and gold nanoparticles were chosen as nanoparticles-fillers.

The spectral dependences of the transmittance of CsI, AgCl, KRS-5 and KRS-6 single crystals in the infrared (IR) and terahertz (THz) ranges have been measured. The spectral dependences of the absorption (attenuation) coefficient of these crystals were calculated in the spectral range of 200–3000 μm. It was found, that these crystals are transparent in the millimeter range, which makes it possible to use materials when working with THz radiation. It should be noted that, in contrast to the IR spectral region, the optical quality of the surface of the crystal samples practically does not affect the transmission in the millimeter range.

In this work, the shielding properties of mesh structures with various cell sizes on a K108 glass substrate are studied. The transmission spectra of the samples were obtained in a frequency range from 1 GHz to 1620 THz. A comparison of the experimental transmission spectra with those obtained using several theoretical models, and a numerical calculation were carried out. The most optimal theoretical model used to describe the shielding properties of a mesh structure in the frequency range upper-bounded by a resonant frequency is the one-mode calculation model. Anti-reflection coatings were used to increase the transmission coefficient of the structures in the visible and near-IR spectral ranges. These mesh structures can be used to shield optoelectronic devices such as a video camera or a laser rangefinder from microwaves.

The transmission in the terahertz (THz) region (up to 3000 μm) of alkali halide monocrystals of sodium chloride (NaCl), potassium chloride (KCl), potassium bromide (KBr) and rubidium iodide (RbI), widely used in the infrared region, was studied. The dependences of the absorption coefficient of these materials in the range 0.9 – 3000 μm were obtained. Near 1000 – 3000 μm, the studied materials are transparent, which allows them to be used in THz devices of the millimeter range.

The transmission of THz (to 3000 μm) radiation by alkali halide single crystals of sodium chloride (NaCl), potassium chloride (KCl), potassium bromide (KBr), and rubidium iodide (RbI), which are widely used in the IR spectral region, is studied. The spectral dependences of the absorption coefficients of these materials in the range of 0.9–3000 μm are determined. These materials are transparent in the range of 1000‒3000 μm, which makes it possible to use them in terahertz (millimeter) devices.

The novel approaches to study the II–VI-based laser heterostructures using cathodoluminescence and electron probe microanalysis techniques are described in detail. The heterostructures were grown by molecular beam epitaxy on GaAs (001) substrates and consist of bottom and top ZnMgSSe cladding layers and ZnCdSe/ZnSe quantum well embedded in Zn(Mg)SSe/ZnSe graded index waveguide. The microanalysis technique based on the intensity measurements of characteristic X-rays has been applied to determine both the composition of ZnCdSe quantum well layer and its position within heterostructure. The depth resolved cathodoluminescence technique has been applied for the transport studies of electron beam generated carriers in heterostructure. The cathodoluminescence intensity of ZnCdSe quantum well has been measured as a function of electron beam energy. The Monte-Carlo simulations of carrier generation distribution within the heterostructure under electron beam irradiation have been used for fitting of experimental results. It made possible the nondestructive characterization of the multilayer heterostructure to estimate both deficiency and carrier transport length.

The cathodoluminescence technique to study the ZnSe-based laser heterostructures is described. The heterostructures were grown by molecular beam epitaxy on GaAs (001) substrates and consist of bottom and top ZnMgSSe cladding layers and ZnCdSe/ZnSe quantum well or CdSe/ZnSe quantum dots sheets placed inside Zn(Mg)SSe/ZnSe graded index waveguide. The transport of charge carriers generated by electron beam in heterostructure was investigated using depth resolved cathodoluminescence. For that the dependence of cathodoluminescence intensity of active region on electron beam energy has been simulated using Monte-Carlo calculation of carrier distribution on depth. It made possible the non-destructive characterization of multilayer heterostructure quality, to estimate both deficiency and carrier transport. (C)12 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Electron beam methods, such as cathodoluminescence (CL) that is based on an electron-probe microanalyser, and (200) dark field and high angle annular dark field (HAADF) in a scanning transmission electron microscope, are used to study the deterioration of interfaces in InGaP/GaAs system with the GaAs QW on top of InGaP. A CL emission peak different from that of the QW was detected. By using HAADF, it is found that the GaAs QW does not exist any longer, being replaced by extra interlayer(s) that are different from GaAs and InGaP because of atomic rearrangements at the interface. The nature and composition of the interlayer(s) are determined by HAADF. Such changes of the nominal GaAs QW can account for the emission observed by CL.