Dipole azinylmethylenemalononitrile-based chromophores with various fused azine (quinoline, quinoxaline and pyrido[2,3-b]pyrazine) moieties and bulky TBDPS-ethyl group in aniline donor fragment have been synthesized. Nonlinear optical (NLO) activity of poled PMMA films doped with such dyes has been investigated by second harmonic generation technique with in two approaches. Composite materials exhibit the growth of NLO performance at increasing dyes load from 25 wt% to 35 wt%. Polymer films doped with quinoxalin(on) ylmethylenemalononitrile-based chromophores demonstrate enhanced values of NLO coefficients, d33, up to 85 p.m./V.

Azo-functionalization of aniline-containing methacrylic copolymers yielded polymers with side-chain chromophore contents ranging from 4.4 to 39 mol%. The highest nonlinear optical coefficient was achieved with a chromophore content of 17 mol%. The resulting polymers demonstrated good relaxation stability at elevated temperatures: 98 and 86% at 55 and 65 degrees C, respectively.

D-π-A chromophores based on novel macroacceptors − fused azinylmethylenemalononitriles (fused azine = pyrido[2,3-b]pyrazine, quinoline, quinoxaline and quinoxalin-2-one) − have been synthesized and their linear and nonlinear optical properties in gas, solution and in poled PMMA-based films have been investigated by DFT, UV-vis and second harmonic generation technique. The transition from chromophores with an azine acceptor to ones with azinylmethylenemalononitrile acceptors leads to a 10-fold increase in calculated μβ values. Poled polymer films doped with studied chromophores at 25wt% load exhibit quadratic nonlinear optical activity with d33 values up to 42 pm/V.

All three components of the refractive index of a GUHP crustal in the visible, near-infrared, and terahertz spectra were thoroughly studied. The results obtained allow for the calculation with high accuracy of phase matching conditions for nonlinear frequency conversion of different laser sources.

Novel D–π–A–π–A′ chromophores with different substituents in the donor moiety were synthesized and NLO coefficients for composite polymer materials doped with them were measured.

Subject of study. A holographic system with a tunable convergence angle of two interfering light beams, based on a beam-splitting cube and intended for writing diffraction gratings, is investigated analytically. The initial light beam is introduced into the cube using a movable mirror, which performs both linear and angular displacements, because of which the convergence angle is tuned. A lever mechanism leaning on an inclined guide is used for the movable mirror's combined movement. Aim of study. The primary aim is to find a matching technique for the displacements of the movable mirror that ensures the resulting interference grating created in the plane of complete mutual overlap of converging beams remains immobile when the convergence angle is adjusted. Method. The path of light beams in the system was analyzed within the framework of geometric optics. Main results. It was found that the contact profile of the guide must be curvilinear to fix the spatial position of the interference grating. The precise functional relationship describing the envelope of this profile is derived, and the tuning characteristics are calcu-lated based on the relative position of the photosensitive sample with respect to the beam-splitting cube. Practical significance. The design of this holographic system presents the advantage of using light beams of various diameters without requiring system corrections.(c) 2023 Optica Publishing Group

Nonlinear optical crystals of gallium selenide are efficient up- and downconverters of infrared and terahertz frequencies. Their nonlinear properties have been investigated at wavelengths within the main transparency window. However, insufficient attention has been paid to studies at the telecommunication wavelength, especially for sulfur-doped crystals. Closing this gap, we report on the optical and electro-optical properties of GaSe(1–x)Sx crystals (where x = 0, 0.03, 0.12, 0.16, and 0.22). For this purpose, the refractive indexes of the ordinary waves at terahertz frequencies and at a wavelength of 1.55 μm have been measured. The detection efficiency of the subterahertz waves in the crystals was studied using Er-fiber laser pulses and compared with that of GaAs, the etalon electro-optical crystal, at this wavelength. This allows us to estimate the dependence of the electro-optic coefficient r22 of GaSe(1–x)Sx on the sulfur concentration. It was shown that the sample with x = 0.12 has the largest value of the electro-optical coefficient r22 = 1.26 pm/V and provides the highest detection efficiency among the samples. The potential of employing S-doped GaSe crystals as nonlinear optical converters for photonic devices operating at telecom wavelengths is discussed.

The information on the refractive index of a photoresist is useful for a number of applied problems of control of technological processes in microelectronics, as well as for experimental research of the characteristics of prototyped diffractive and microoptical structures with a deep microrelief. Since this optical parameter depends on the processing conditions of the photoresist, the spectral dependences provided by manufacturers sometimes may be insufficient. We present the results of determining the dependence of the refractive index of positive photoresists S1818 G2 (MICROPOSIT) and FP-3535 (FRAST-M) in the wavelength range of 500–1600 nm on the conditions of the preliminary heat treatment regime with a duration of 15–30 min and exposure to actinic radiation. We sugggest the processing parameters for the studied photoresists to obtain a refractive index within 1.61–1.64 in the visible and 1.59–1.61 in the infrared ranges of the radiation spectrum. An anomalous dispersion zone in the wavelength range of 570–640 nm was found in films of S1818 G2 dyed photoresist, which is often used in the experimental study of characteristics when prototyping diffractive optical elements. The dependences of the refractive index of the Russian photoresist FP-3535 were obtained for the first time.

В настоящей работе проведено исследование фазового состава и структуры сплава Ir-16,7 ат. % Ce со стехиометрией CeIr5. Методом рентгенофазного анализа установлено, что сплав не является однофазным, в нем присутствуют в значимых количествах три фазы – CeIr5, Ir и Ce2Ir7. Сплав имеет поликристаллическую структуру, зерна состоят из высокодисперсной эвтектической смеси двух фаз CeIr5+ Ir. Интерметаллид CeIr5 образует матрицу, в которые включены кристаллы Ir. Кристаллы Ir имеют глобулярную и игольчатую форму. Характерный размер глобулярных кристаллов 1-3 мкм, диаметр игольчатых кристаллов 0,5-1,0 мкм. При выходе на поверхность фотокатода иглы Ir образуют столбчатую структуру с радиусом кривизны около 400 нм и плотностью ρ = 33·104 мм-2. Дисперсность структуры обеспечивает большую плотность межфазных границ. Оценка показывает, что на поверхности площадью 1 мм2 длина сети межфазных границ составляет 0,83 м.

Subject of study. Volumetric thermochemical laser writing of nanostructured reflective diffraction gratings in a dual-layer Zr/SiO2 material is studied. Objective. Direct laser writing on thin zirconium films on fused silica substrates is comprehensively studied to determine the cause of the anomalously large phase shift and investigate the possibility of creating reflective diffraction structures on its basis with a potential application in the compo-nent base of photonics. Method. Thermochemical writing with a focused laser beam on zirconium films deposited on fused silica substrates makes it possible to form oxide micropatterns. Depth measurements of their relief on an atomic force microscope show a surface reliefno more than 10 nm deep. In contrast, measurement on a white light interferometer shows a relief up to hundreds of nanometers deep. Scanning electron microscopy and Raman spectra analysis provide information on the modified regions' internal structure and chemical composition. Main results. The effect of laser writing of nanostructured reflective diffraction gratings on a dual-layer material is three-dimensional because the layer is modified in depth by 50%-60% more than the initial thickness of the Zr film. In addition, gratings with a period equal to the laser beam scanning step are formed on the surface and in the depth of the modified layer. Depending on the power of the writing beam, the modified layer comprises a compo-sition of oxide and zirconium nitride in the amorphous or crystalline phases, including silicon oxide in the lower layer. The inner grating comprises channels in the modified layer, with a cross-section of approximately 80 nm. A hypothesis about the morphology and mechanism of the formation of nanogratings has been proposed. Practical significance. Supplementing the "dry" one-stage technology for manufacturing binary reflective diffraction struc-tures on a dual-layer Zr/SiO2 material with a stage of reactive ion etching for diffraction efficiency adjustment is achieved. (c) 2023 Optica Publishing Group

Метод спектральных временных окон для исследования сложных динамических процессов1 Институт автоматики и электрометрии СО РАН, г

Impact of pi-deficient heterocyclic core (A') in conjugated bridge of D-p-A'-p-A chromophores (D = N,N-dihexylaniline, A = tricyanofuran derivative) on optical and thermal properties has been investigated. Three new chromophores with vinyl-hetaryl-vinyl bridges containing pi-deficient benzoazine moiety (quinoxaline, quinoxalinone and quinoline) have been synthesized along with new chromophores with vinyl-thiophene-vinyl bridge containing pi-excessive heterocycle and short vinylene bridge, and their properties are compared to reveal the role of pi-deficient hetaryl moiety. Their linear optical properties were systematically investigated by UV-Vis spectroscopy and molecular nonlinear optical (NLO) characteristics were predicted by DFT calculations. As the aromaticity of the heterocycle in the bridge increases, a hypochromicity and hypsochromic shift of the absorption maximum manifest themselves in the UV-Vis spectra, the origin of electron transitions was studied by TD-DFT with CAM-B3LYP and PBE0 density functionals. The calculated first hyperpolarizability, beta(tot), for A' = quinoxaline, quinoline and thiophene, was shown to be almost independent on the type of the p-bridge core, being in a narrow interval 800-831 center dot 10(-30) esu, while for A' = quinoxalinone beta(tot) is essentially higher (996 center dot 10(-30) esu). All chromophores exhibit good thermal stability (T-d > 192 degrees C). Thin films of composite polymer materials with PMMA matrix and studied chromophores as guests as well as of some molecular glasses were spin-cast and corona-poled, and their quadratic NLO activity was measured by two different techniques. For materials with guest chromophores containing quinoxalinone, quinoxaline and thiophene moieties in the bridges NLO coefficients d(33) were found to be rather close and reached 76 pm/V, what is almost 3 times higher than that for polymer film with quinoline-based chromophore. Rather high values of NLO coefficients for molecular glasses based on chromophores with quinoline, thiophene and quinoxalinone cores were obtained: 52, 124 and 132 pm/V, respectively, which notably exceed the values for composite materials with these chromophores as guests.

Results of experimental works on studying concentration dependences and temporal and thermal stability of the quadratic response of guest–host materials based on polycarbonate and original synthesized dyes are presented. It is shown that chromophore modifications by dendron lateral substituents significantly improve solubility, which allows one to create materials with a high content of optically active particles. The materials possess high temporal and thermal stability and exhibit $$d_{33}$$ of up to 80 pm/V at a chromophore density of $$2{.}5\times 10^{20}$$ cm $${}^{-3}$$ .

We studied terahertz (THz) optical and dielectric properties of stoichiometric lithium tantalate (sLT) from room down to liquid nitrogen temperature in the range of 0.15–1.8 THz using terahertz time-domain spectroscopy. Two-oscillator Lorentz models were fitted well to the crystal properties for both ordinary and extraordinary waves. We also studied changes in sLT ultraviolet (UV) absorption from room to liquid nitrogen temperature. The measurements showed a significant drop in absorption in both the THz and UV ranges with cooling. According to these results cooling should increase lithium tantalate potential in optical-to-terahertz conversion of high-power 800-nm radiation. The measured properties can be used in designing nonlinear optical conversion schemes and devices based on sLT.

Photocathodes made of the Ir-Ce system alloys have high thermal resistance, electrical, and thermal conductivity along with high electron emission properties and are widely used as sources of electrons. In this paper, the phase composition and structure of the Ce-83,3ат%Ir alloy intended for use as a photocathode material are studied. The alloy obtained by electron beam melting has a component ratio corresponding to the CeIr5 intermetallic compound. Despite this, a dispersed multiphase material is formed during crystallization. X-ray phase analysis shows the presence of three phases, such as Ir, CeIr5, and Ce2Ir7, in the photocathode material. Optical microscopy studies of the photocathode microstructure reveal that the basis of the alloy is the CeIr5 + Ir eutectic. The CeIr5 phase forms a matrix in which Ir crystals are included. The Ir phase has the form of rods with an average diameter of 0.7 microns. The high dispersion of the structure can increase the emission properties of the photocathode.