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Urea-doped barium tartrate (UBT) crystals were developed using the method of an aqueous solution. The crystal structure was determined through XRD analysis. Optical transmittance studies were conducted to analyze multiple linear optical parameters such as transmittance, band gap, refractive index, absorption coefficient and more. Vickers microhardness testing was performed to assess mechanical properties like hardness and yield strength. The efficiency of Second harmonic generation (SHG) was calculated for the harvested crystal. Laser damage threshold (LDT) testing was completed as well. Nonlinear optical characteristics were analyzed by applying the Z-scan method. Electronic polarizability was calculated for the UBT crystal.

A new optically nonlinear material, poly[N-(4-benzoylphenyl)-2-methylacrylamide], for conversion of wavelength 1064 nm to 532 nm has been synthesized. The material possesses strong electrical and optical nonlinearity required for second harmonic generation (SHG). The thin films of poly[N-(4-benzoylphenyl)-2-methylacrylamide] were prepared by the vacuum-deposition technique. The optical UV-visible, IR, NMR studies, mass spectrometry, surface topography and nonlinear optical properties of the thin films were studied. The vacuum-deposited thin films of the polymer were subjected to optimized high potential multi-point corona poling at temperatures just below the glass transition temperature (T_g) to create directional orientation of the side chain groups. The optical UV-visible absorption indicates a complete transparency in the visible and IR regions with an absorption peak at ~350 nm. The energy band gap of the polymer was estimated to be ~2.9 eV, from the optical absorption spectra of the thin films. The electrical current–voltage (IV) and optical nonlinear characteristic indicate the strong potential of these polymeric thin films for nonlinear optical (NLO) applications.

The cyano and nitro groups were chosen as acceptor groups, and the substituent amino or ether groups as donor groups to the matrix. Polyurethane (PU) was modified by glycerol to increase the content of chromophore and to improve the stability of the nonlinearity. T_g and T_m were raised and solubility, film-forming ability and other physical properties were improved. The average functional groups of the reactant can be adjusted to ≥ 2 with polygroups and monogroups mixture. These poled polymers show high second-order optical nonlinearity and would have potential application in frequency-doubling or electro-optical controlling devices.

A nonlinear optical (NLO) microscope has been developed based on recording the second harmonic generation (SHG) signals of the B₂- and B₄-phases of bent shaped liquid crystalline (LC) materials. We observed that the microstructures of the polar order can be accurately characterized by 2D scanned images implementing this device. Specifically, we have investigated two bent-core compounds, which have either B₄ or B₂ phases at room temperature and exhibit SHG activity. The NLO microscope was calibrated according to the Maker-fringes method allowing the in situ evaluation of the relative SHG efficiency. The developed NLO microscopy device may serve as an important tool to characterize liquid crystalline features at a microscopic scale for both fundamental and applied research.

A nonlinear optical (NLO) microscope has been developed based on recording the second harmonic generation (SHG) signals of the B₂- and B₄-phases of bent-shaped liquid crystalline (LC) materials. We observed that the microstructures of the polar order can be accurately characterized by 2D scanned images implementing this device. Specifically, we have investigated two bent-core compounds, which have either B₄ or B₂ phases at room temperature and exhibit SHG activity. The NLO microscope was calibrated according to the Maker fringe method allowing the in situ evaluation of the relative SHG efficiency. The developed NLO-microscopy device may serve as an important tool to characterize liquid crystalline features at a microscopic scale for both, fundamental and applied research.

A theoretical analysis of the condition of scalar phase-matched second harmonic generation and optical parametric oscillation (OPO) in single-crystalline samples Zn_0.52Mg_0.48Se is presented. The calculated range of pumping for second harmonic generation with phase matching is 5.1-13 μm. The tuning range of the optical parametric oscillator based on Zn_0.52Mg_0.48Se is determined. The combination of active media and nonlinear converter for OPO in the same optical element are proposed.

Here, we propose a novel plasmonic structure, called asymmetric plasmonic nanocavity grating (APNCG), which is shown to dramatically enhance nonlinear optical process of second harmonic generation (SHG). The proposed structure consists of two different metals on both sides of lithium niobate and a thin layer of graphene. By using two different metals the nonlinear susceptibility of the waveguide would be increased noticeably causing to increase SHG. On the other hand, it consists of two identical gratings on one side. By two identical gratings, the pump beam is coupled to two opposing SPP waves, which interfere with each other and result in SPP standing wave in the region between the two gratings. The distance between two gratings will be optimized to reach the highest SHG. It will be shown that by optimizing the geometry of proposed structure and using different metals, field enhancement in APNCG waveguides can result in large enhancement of SHG.

The advancement of crystal growth and characterization methods allows us to investigate new substances with excellent nonlinear optical characteristics. To synthesize nonlinear optical material L-histidine hydrochloride hydrate (L-HHCLH), the gradual evaporation process was used. The produced samples were characterized by single-crystal X-ray crystallography, Fourier transform infrared (FTIR) and Raman spectroscopy, UV–visible (UV–Vis) spectroscopy, second harmonic generation (SHG) test, dielectric, and mechanical investigations. The L-HHCLH sample was crystallized in an orthorhombic structure with the P2₁2₁2₁ space group, as verified by the crystallographic data. FTIR and Raman spectroscopy were applied to examine the molecular vibrations and availability of the functional groups of the compound. The L-HHCLH is significantly transparent across the UV and visible ranges, as shown by the UV–Vis spectra measurements. The bandgap of L-HHCLH is 5.45 eV. The SHG test showed that the L-HHCLH crystals produced a significant amount of SHG output thrice that of the potassium dihydrogen phosphate (KDP) sample. The frequency dependences of the dielectric parameters were investigated in the dielectric tests. With increasing frequency, both the dielectric constant and loss dropped exponentially. The crystal hardness was determined using a microhardness test.

The development of crystal growth and measurement methods opens new possibilities for studying materials with remarkable nonlinear optical features. The development of bulk crystals is a constant concern to be beneficial for device applications. This study focuses on the development of nonlinear optical crystals of L-histidine complexes, characterization approaches, and prospective applications. The solution growth approach, a straightforward, inexpensive, and low-temperature growth technique, was adopted broadly. Recent studies show that L-histidine derivatives have potential optical, SHG, thermal, dielectric, and mechanical properties, making them an excellent choice for nonlinear optical devices. In this work, structural, spectroscopic, chemical composition, linear and nonlinear optical analyses, thermal, and dielectric characterizations of L-histidine derivatives were conducted. Most of the L-histidine complexes were found to be crystallized in orthorhombic and monoclinic crystal systems with P2₁2₁2₁ and P2₁ space groups. The crystalline perfections of the samples were analyzed by the HR-XRD method. The energy-dispersive X-ray (EDX) spectroscopic technique was applied to evaluate the chemical content of the compounds. FT-IR and FT-Raman techniques were used to recognize the molecular vibrations and functional groups of the L-histidine derivatives. The UV-visible and photoconductivity studies were done to examine the optical behaviors of the developed crystals. Most of the crystals were found to have excellent optical transparency and wide bandgaps. It has been observed that L-histidine hydro-fluoride dehydrate and L-histidine tetrafluoroborate are found to have the highest second harmonic generation (SHG) efficiencies. The dielectric analyses were utilized to study the dielectric constant and dielectric loss variations with the applied frequency. According to the thermal analyses, most of the crystals were found to have substantial thermal stabilities suitable for device applications.

2-methylimidazole (2MI) single crystal has been successfully grown by slow evaporation solution technique (SEST) by using water as a solvent. The synthesized 2MI crystal was purified by repetitive recrystallization. Various other characterizations were carried out for the grown 2MI single crystal, such as powder X-ray diffraction (PXRD), FTIR, UV–Visible NIR, Microhardness, Photoluminescence, SEM, Piezoelectric, and SHG. The 2MI crystal was subjected to PXRD to endorse the crystalline quality of the material. The vibrational assignments and their functional groups were identified from the FTIR analysis. The UV–Visible NIR study exposes the transparency and cut-off wavelength of the 2MI crystal. The mechanical strength was investigated by Vickers microhardness tester. The surface investigation of the 2MI crystal was analyzed by a scanning electron microscope technique to obtain the presence of defects and surface texture in the developed 2MI crystal. The photoluminescence spectrum confirmed the green light emission of the crystal. The value of the piezoelectric d${}_{33}$ coefficient is measured using piezoelectric analysis. Kurtz powder’s second harmonic generation test reveals that the frequency conversion efficiency of 2MI is 3.7 times higher than that of potassium dihydrogen phosphate (KDP) crystal.

The development of crystal fabrication and characterization approaches makes it possible to study novel materials with enhanced linear and nonlinear optical properties. The solution growth method was adopted in the present investigation to create Barium thiourea chloride (BTCL), a metal–organic single crystal. Structural, optical, and thermal characteristics of the BTCL crystals were evaluated by XRD analysis, Fourier transform infrared spectroscopy, UV–Vis spectrometry, photoluminescence, SHG, and thermal analyses. The XRD method was applied to investigate the structural characteristics of the BTCL, which is related to the monoclinic structure. The FT-IR spectral investigation was conducted to observe the vibrational modes in BTCL. The optical measurements showed the transmittance in the near-UV and visible spectrums. Optical characteristics include bandgap, refractive index, extinction coefficient, optical, and electrical conductivities, and dielectric constants were obtained. The PL curve showed two notable emission peaks at 482.5nm and 491nm. The ability to generate second harmonics was investigated using the Kurtz and Perry method, and the SHG was more than 1.79 times the KDP sample. The thermal behavior of the BTCL was evaluated by TGA/DTA measurements. The Coats–Redfern relation was used to estimate the activation energy of the thermal system and the value was determined to be 9.48KJ/mol. The findings indicate that the BTCL crystals possess excellent optical transparency, higher SHG potency, and good thermal stability, which are suitable for use in photonic structures.