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The optimal geometries of vector phase matching are determined for the cases of second harmonic, sum and difference frequency generation in a number of orthorhombic nonlinear optical crystals - KTP, KTA, KB5, KNbO3, LBO, CBO, LRB4. Extreme surface method was used to define wave vectors directions of highest possible generation efficiency. As it is shown, in a significant number of cases vector phase matching ensures higher efficiencies than the scalar one.

We report the synthesis, structure and nonlinear optical properties of cadmium sulphide (CdS) nanocrystallines (NCs) synthesized electrochemically both with and without detergent ATLAS G3300. Relevant structural and morphological features are explored by X-ray diffraction and scanning electron microscopy (SEM) techniques. The efficiency of the second harmonic generation (SHG) appears to be strongly dependent on the energy density of the incident fundamental laser radiation and NC sizes., Comment: 2020 IEEE 15th International Conference on Advanced Trends in Radioelectronics, Telecommunications and Computer Engineering (TCSET), Conference Location: Lviv-Slavske, Ukraine, 25-29 February 2020, 5 pages, 8 figures, 3 tables

Photonic metamaterials with properties unattainable in base materials are already beginning to revolutionize optical component design. However, their exceptional characteristics are often static, as artificially engineered into the material during the fabrication process. This limits their application for in-operando adjustable optical devices and active optics in general. Here, for a hybrid material consisting of a liquid crystal-infused nanoporous solid, we demonstrate active and dynamic control of its meta-optics by applying alternating electric fields parallel to the long axes of its cylindrical pores. First-harmonic Pockels and second-harmonic Kerr birefringence responses, strongly depending on the excitation frequency- and temperature, are observed in a frequency range from 50 Hz to 50 kHz. This peculiar behavior is quantitatively traced by a Landau-De Gennes free energy analysis to an order-disorder orientational transition of the rod-like mesogens and intimately related changes in the molecular mobilities and polar anchoring at the solid walls on the single-pore, meta-atomic scale. Thus, our study evidences that liquid crystal-infused nanopores exhibit integrated multi-physical couplings and reversible phase changes that make them particularly promising for the design of photonic metamaterials with thermo-electrically tunable birefringence in the emerging field of spacetime metamaterials aiming at a full spatio-temporal control of light., Comment: 12 pages, 6 figures

Combining dielectric crystals with mesoporous solids allows a versatile design of functional nanomaterials, where the porous host provides a mechanical rigid scaffold structure and the molecular filling adds the functionalization. Here, we report a study of the complex lattice dynamics of a SiO$_2$:KH$_2$PO$_4$ nanocomposite consisting of a monolithic, mesoporous silica glass host with KH$_2$PO$_4$ nanocrystals embedded in its tubular channels $\sim$12 nm across. A micro-Raman investigation performed in the spectral range of 70-1600 cm$^{-1}$ reveals the complex lattice dynamics of the confined crystals. Their Raman spectrum resembles the one taken from bulk KH$_2$PO$_4$ crystals and thus, along with X-ray diffraction experiments, corroborates the successful solution-based synthesis of KH$_2$PO$_4$ nanocrystals with a structure analogous to the bulk material. We succeeded in observing not only the high-frequency internal modes ($\sim$900-1200 cm$^{-1}$), typical of internal vibrations of the PO$_4$ tetrahedra, but, more importantly, also the lowest frequency modes typical of bulk KH$_2$PO$_4$ crystals. The experimental Raman spectrum was interpreted with a group theory analysis and first-principle lattice dynamics calculations. The analysis of calculated eigen-vectors indicates the involvement of hydrogen atoms in most phonon modes corroborating the substantial significance of the hydrogen subsystem in the lattice dynamics of paraelectric bulk and of KH$_2$PO$_4$ crystals in extreme spatial confinement. A marginal redistribution of relative Raman intensities of the confined compared to unconfined crystals presumably originates in slightly changed crystal fields and interatomic interactions, in particular for the parts of the nanocrystals in close proximity to the silica pore surfaces., Comment: 10 pages, 4 figures, in press

This article considers the issue of the development, production, and application of nanocomposite materials in telecommunication networks for the optical and subterahertz wave ranges. The results are obtained on the base of growing the nanocomposite materials from Al2O3 membranes and KDP crystals in a saturated solution.

In the paper, we explain an automated LabVIEW controlled setup that enables interferometric measurements of refractive indices in crystalline materials using a laser light source. The setup combines a mechanical system, a microcomputer-controlled gearless drive, a Michelson interferometer, an optical detector, a data acquisition system and a LabVIEW virtual instrument for an accurate non-destructive determination of the refractive index of given plane-parallel samples. We explain a concept, implementation, and hardware/software peculiarities of the developed system. Test experiments on different crystals yielded results that are in good agreement with available reference data. The range of potential applications of the proposed setup extends from fundamental optical research to biophotonics instrumentation, where efficient delivery of light is of crucial importance and reliable automated probing tools are needed for optical components characterization.

In this paper the state-of-the-art for exploiting the unique physical and chemical properties of crystalline materials and their possible applications for development of crystalline nanocomposites with the tailored anisotropy were discussed. Using a method of growing crystals from a solution the KDP and TGS nanocrystalites were grown in the mezopores of the Al2O3 matrix. To investigate the developed nanocrystalline samples the X-ray analysis was used. A form of the obtained diffractograms and our calculations show the predominant crystallization of the KDP and TGS in the direction [100], which coincides with the direction of the cylindrical pores. Thus, diffractograms contain only reflexes of crystallographic planes (200) and (400). The achieved result indicates the possibility of growing of nanocrystals in mesopores of such Al2O3 structures developed by us and provides the prospect of creating optical cells with increased energy efficiency.

A principal possibility of formation the nanostructures on the surfaces of 50PbO-25Bi$_2$O$_3$-20Ga$_2$O$_3$-5BaO (doped by Eu3+, Er3+, Dy3+) is demonstrated by using multi-coherent beams. As a sources of the photoinducing coherent light we have used nanosecond Nd:YAG and Er:Yb lasers generating at 1064 nm and 1540 nm, respectively. The morphology of the photoinduced surfaces is sensitive to the type of rare earth ions. The thickness of the layer was about 20-30 nm. Possible mechanisms are explained by coherent photoinduction of the valence electrons.

In this paper, the technology of growing ammonium dihydrogen phosphate (ADP) crystals in pores of nanoporous aluminum oxide (Al2O3) matrices was presented. On the grown nanocomposites, the optical properties of such structures were studied. In particular, the direct and diffuse optical transmission, as well as specular reflection of Al2O3 matrices with ADP crystals grown in nanopores, were analyzed. From the performed experimental studies, it can be concluded that the transmission and scattering of pure Al2O3 porous matrices and with ADP crystals in nanopores depends largely on the properties of the Al2O3 matrices and the technology of their production.