Optics and Spectroscopy最新文献

A simulation of remote atmospheric gas analysis in the spectral range near the wavelength of 1572 nm has been performed. The characteristics of a narrow-band thermostable continuous laser diode with an output power of ≤15 mW have been experimentally studied, and the possibility of tuning the laser diode wavelength both within a separate isolated CO₂ absorption line and from line to line in the CO₂ absorption band has been shown. The possibility of using a laser diode for further work on the creation of a lidar sensor for studying the CO₂ content in the atmosphere has been shown.

The characteristics of a planar optical resonator made of quartz glass surrounded by silver mirrors have been studied when their thickness was varied. The frequency responses of band-pass filters on planar structures obtained by vacuum deposition on quartz glass (SiO₂) substrates of three quartz layers, which are half-wavelength resonators separated from each other, from the substrate, and from the free space by four layers of silver (Ag), were measured. The thicknesses of the Ag and SiO₂ layers were determined on the basis of the specified filter passband parameters by synthesizing one-dimensional models using electrodynamic analysis. The experimental frequency dependencies of the real and imaginary parts of the complex permittivity of silver have been considered. The measured frequency responses of the manufactured prototypes of red, green, and violet filters are in good agreement with the characteristics obtained during synthesis. Systematic studies of filters with a central passband frequency of 300 THz (wavelength of 1 µm) and a relative bandwidth of 2‒20%, containing from 3 to 6 resonators, have been carried out. The high performance of the developed filters demonstrates their potential for their use in optical devices.

In this work, the relaxation process in mixtures of a nematic liquid crystal matrix with additives of azochromophores and CdSe/ZnS quantum dots is analyzed. The thermally initiated mesophase—isotropic liquid phase transition showed that the activation energy of this process increases almost equally upon the addition of AX-7 or AX-8 in an amount of 10 wt %. However, the photoinduced phase transition into isotropic state, analyzed by dielectric spectroscopy, demonstrates a significant difference when different azochromophores are present in the system as confirmed by activation energy values. This effect is associated with changes in the ratio of trans–cis-isomers. IR-spectroscopy revealed the unexpecting predominance of cis-isomers in AX-7, while trans-isomers are typical for AX-8. This difference was explained by a change in the distribution of electron density in the azochromophore fragments, taking into account the influence of aromatic ring substituents.

Electrodynamic modeling of the interaction of microwaves with a nonlinear distributed semiconductor inclusion (a Gunn diode of planar geometry) in a strip-slot structure has been carried out by solving a nonlinear 3D diffraction problem (Maxwell’s equations together with the equation of motion of charge carriers in a semiconductor) using a computational algorithm developed by the cross-sectional method. Using the method of nonlinear autonomous blocks with Floquet channels, the results of electrodynamic calculations of the amplitudes of reflected waves (at the input sections of a planar Gunn diode) of the fundamental type of the first and three higher harmonics depending on the longitudinal size of the semiconductor inclusion in the strip-slot line have been obtained.

A model including the graphene complex permittivity tensor has been developed in MWS CST and the efficiency of magnetic field tunability of metasurfaces made of graphene 1D nanoribbons has been modeled depending on the induction of the applied magnetic field and the period, size of the nanoribbons in the THz and far-infrared ranges.

A parametric light oscillator based on a ZGP single crystal pumped by Ho:YAG laser radiation was created, which generates radiation according to type II synchronism with smooth tuning in the spectral generation range with a width of the generated radiation of 1 cm^–1 due to the use of intracavity radiation selection using a Lyot filter. The pulse energy of the generated radiation was 0.08 mJ at a pulse repetition rate of 10 kHz and a pulse duration of 26 ns. The tuning range was from 3.3 to 4.2 μm. The divergence of the generated radiation did not exceed 1.5 mrad.

Dielectric mirrors with an oxide coating for a parametric light generator based on a ZnGeP₂ single crystal were fabricated. The threshold values of laser-induced breakdown of dielectric mirrors made for single-pass (no. 1) and multi-pass (no. 2) resonators (3.5 ± 0.1 and 3.9 ± 0.1 J/cm², respectively) are determined. Based on the obtained data, the mirrors were tested in the OPO system based on the ZnGeP₂ single crystal. The maximum generation efficiency achieved in the experiment was ~54% when using mirror no. 1 and 50% when using mirror no. 2. In this case, the average power of the generated OPO radiation was 7.7 and 3.7 W when using mirror no. 1 and mirrors no. 2, respectively. The possibility of creating a dielectric mirror with high radiation strength operating in the range of 3.5–5 μm on a sapphire substrate is shown.

The design of an interference coating made of a pair of Nb₂O₅/SiO₂ materials on a quartz glass substrate has been simulated. A dichroic mirror has been created on the basis of the calculated design with reflection coefficients R < 1% and R < 99.6% for the spectral ranges 1600–1750 and 2050–2100 nm, respectively.

The dispersions of the refractive index and absorption coefficient were determined for monolayers of titanium oxide and silicon oxide. The design of a multilayer antireflective optical coating for these materials in the spectral range of 0.4–8 μm has been developed. Modes for applying coating using ion-beam sputtering onto a semiconductor substrate have been selected. The optical characteristics of a four-layer interference coating with antireflection coating on a ZGP substrate were measured in the range of 2097 nm and 3.5–5 μm, with residual reflection R ≤ 0.2% and R ≤ 2.1%, respectively. Tests were carried out for adhesion and abrasion of the coating in accordance with GOST.

The mesomorphic, optical, orientation, and dielectric properties of a nematic liquid crystal (LC) of 4-pentyl-cyclohexyl-4-benzonitrile (5PCH) doped with optically active (bis)camphoralidene-ethylenediamine (C2-bisCamN) have been studied. On the basis of the analysis of mesophase textures, the chiral nematic induction has been detected with the addition of dopant. The helical pith of the induced chiral nematic in mixtures has been measured by the Grandjean–Cano method and the helical twisting power has been estimated. It has been shown that the chiral induction effectiveness decreases with increasing dopant concentration because of association. The clearance temperatures of the mixtures have been measured and the degree of destabilization of the mesophase with the introduction of dopant was assessed by the method of the polarization thermomicroscopy. The effect of a chiral dopant on the mesophase anisotropic characteristics such as: dielectric permeability and birefringence, has been studied. It has been found that the introduction of C2‑bisCamN and the formation of a chiral mesophase are accompanied by a decrease in dielectric and optical anisotropy and orientational ordering. In this case, the main contribution to the change in anisotropic characteristics has been made by the helical twisting and the local orientation of the “quasi-nematic” layers. The associative state of the mesophase of the binary systems based on the strongly polar cyan derived LCs has been evaluated using the Kirkwood correlation factor. A decrease in the degree of the antiparallel dipole-dipole association of 5PCH with an increase in the concentration of the additive has been shown. The optimized structures of the monomers and dimers of 5PCH, C2-bisCamN, and solvates based on them have been obtained using quantum chemical calculations. Analysis of the geometric parameters (anisotropy of shape and molar volumes), polarity, optical activity, and the stability energies of the monomers and supermolecules has allowed us to identify camphorodiimine associates as the most likely structures responsible for the properties of the induced chiral mesophase in the 5PCH + C2-bisCamN system.