Vol 83, No 3 (2019)

A numerical simulation was performed for frequency conversion of multiline CO laser radiation to the THz range by difference frequency generation in a ZnGeP2 crystal. It was shown that the difference frequencies spectrum can be tuned in the wavelength interval of 70–1300 μm by tuning the phase-matching angle in the range of 11° to 55°. The maximal peak power of difference frequencies radiation (integral over the spectrum) was ~0.23 W at 45° phase-matching angle, which corresponds to a peak power conversion efficiency of 6 × 10⁻⁵.

Factors affecting the operating parameter of a memristor (R_off/R_on) are considered. The increase in this parameter as the current of a magnetron and the period of irradiation are increased while preparing a LiF thin film with copper nanoclusters is studied. The synaptic behavior of a memristor based on this film is demonstrated.

A study is performed of the generation of ultrashort THz pulses in Ti, Ni, and TiNi plates, compared to Au, Ag, Cu plates. The possibility of using them as photosensitive materials in bolometers is considered. Such sources can be used in atmosphere monitoring systems.

Results are presented from studying the parameters of second harmonic radiation under conditions of the transformation of a positively and negatively chirped pulse of fundamental frequency. It is shown that when the duration of a bandwidth-limited pulse (50 fs) is increased to 630 fs and beyond, the distribution of second harmonic intensity becomes close to Gaussian. The efficiency of second harmonic generation with duration of 2.5 ps falls from 38.69 to 4%, and the quality of the second harmonic improves until it becomes equal to М² = 1.3. Substantial modulation of the amplitude and the narrowing of the second harmonic spectrum are observed upon negative chirping of the fundamental frequency.

The results are presented from experimental studies of the emission of NO radicals in a filament of femtosecond radiation produced in a N₂/NO₂ gas medium with total pressures of up to 1 atm. It is shown that in the recorded emission spectrum of the filament, emission transitions A²Σ⁺ (ν' = 0–2) – X²Π (ν'' = 0–5) of NO molecules are observed at concentrations of NO₂ gas of up to 10 ppb⁻¹. It is shown that the intensity of emission of NO A–X molecules grows along with the nitrogen pressure, due to the intermolecular nonradiative transfer of energy from the metastable \({{{\text{A}}}^{{\text{3}}}}\Sigma _{u}^{ + }\) level of a N₂ molecule to the electron A²Σ⁺ level of a NO molecule.

The temperature of phosphor heating as UV radiation is transformed into radiation of the visible range is estimated experimentally. The effect of luminescence quenching as the phosphor temperature rises is used to estimate the degree of phosphor heating directly. It is shown that due to Stokes losses, the phosphor for an LED strip is heated to 15°C when radiation with λ = 337 nm is transformed inside it.

A powerful single-mode distributed Bragg reflector diode laser with a low-noise power supply is developed. The output characteristics of the tapered diode laser are investigated. Using such a laser as a pumping source, the free running mode of a Yb:KYW laser is achieved and investigated. It is shown that a compact precision femtosecond frequency synthesizer based on Yb:KYW laser pumped by a similar type of diode laser can be created.

A study is performed of optical spectra (absorption, excitation, luminescence, energy yield) associated with the upconversion of infrared excitation of 980 nm into visible radiation in crystals of alkaline–earth fluorides CaF₂, SrF₂, and BaF₂, co-doped with YbF₃ (0.01–10 mol %) and HoF₃ (0.01–0.3 mol %). In the 0.1–10 W cm⁻² range of excitation power densities, the intensity of the upconversion bands at 542, 650, and 752 nm grows as the square of the power. A quadratic dependence of the intensity of upconversion on the concentration of Yb³⁺ (0.03–3 mol %) and a weak dependence on the Ho³⁺ concentration (0.01–0.3 mol %) with a maximum at 0.1–0.15 mol % are observed. It is assumed that the upconversion is due to consecutive energy transfer from two closely spaced excited ytterbium ions to the holmium ion.

The temperature dependences of luminescence in slip planes (111) of diamond plates containing nitrogen defects A and B1 upon excitation by a laser with a wavelength of 532 nm were investigated with the use of confocal scanning luminescence microscopy. The red glow of the diamond in the slip planes was dominated by the glow of the center with a zero phonon line (ZPL) of 656 nm at 290 K and the glow of the center with a zero phonon line of 701 nm at 80 K (i.e., spectra were different at different temperatures).

Results from studying the behavior of the hypersensitive ⁵D₀–⁷F₂ transition of Eu³⁺ ions in matrices of double molybdates at different wavelengths of exciting light, and during the transfer of excitation from Tb³⁺ ions to Eu³⁺ ions in double-doped molybdates.

Some manifestations of optical anisotropy in diamond crystals with defects are due to reduction of the symmetry group of the growth pyramid caused by the removal of the orientation degeneracy of defects during tangential growth. In this case, the point symmetry group of the growth pyramid is determined not only by the symmetry group of the growth face, but also by the symmetry of the defects themselves.

A new biodegradable derivative of the biocompatible, biodegradable beta-polysaccharide arabinogalactan is synthesized: arabinogalactan polyaldehyde. Biodegradable hydrogels with chitosan and para-aminobenzoic acid are obtained from the latter. The spectral characteristics of the new compounds and colorimetric tests of their biodegradability by bifidobacteria are discussed.

A noncontact means based on the electrooptical effect and using a photon crystal as a sensor is proposed for measuring the intensity and spatial orientation of high electrical fields of industrial frequency. The possibility of more precise measurements of electrical field gradients up to 10 kV/cm by remote means on the insulation of high-voltage systems is demonstrated.

The local molecular dynamics in a polymer matrix based on polyvinylbutyral for solid polyelectrolyte is studied by means of FTIR spectroscopy. The effect low molecular weight polyethylene glycols with average masses of 200, 400, and 600 g/mol have on the effective size of the free volume elements and the ionic conductivity in the polymer matrix is considered in the context of the free volume model.

The signal of the ultrafast optical Kerr effect (OKE) in liquids, including toluene C₇H₈, nitrobenzene C₆H₅NO₂, and acetonitrile C₂H₃N is analyzed. It is shown that considering the correlation between the orientational and librational responses allows us to determine the rise time of the orientational response associated with the inertial nature of molecular rotations over a time interval of 300–500 fs after the impact of a laser pulse, and to increase the accuracy of determining the form of the Raman spectral density function.

The merging and repulsion of eigenmodes in a multiresonator microwave memory integrated into a waveguide-resonator system are investigated. The merging of eigenmodes is explained on the basis of theoretical modeling and experimental data, and the possibility of controlling the spectral characteristics of the memory is demonstrated.