Growth, Structural, Spectral, Thermal, Optical, Second and Third Order Nonlinear Optical Properties of Imidazolium Hydrogen Squarate (IHS) Single Crystal

Imidazolium hydrogen squarate (IHS) crystal has been grown by slow evaporation solution growth technique at room temperature. The lattice parameters of grown crystal were determined using single crystal X-ray diffraction data and compared with powder XRD. Single crystal XRD shows that the crystal crystallizes in monoclinic system with noncentrosymmetric space group Pc. The crystallinity of the grown crystal was confirmed by X-ray powder diffraction analysis. FT-IR and FT-RAMAN analyses qualitatively confirm the various functional groups present in the grown crystal. The 1H and 13C NMR spectra were recorded to establish the molecular structure. Thermal properties of title crystal were studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The UV-Vis-NIR transmission spectrum was recorded to find the band width of optical transmittance window and the lower cutoff wavelength. The optical band gap value of the material is evaluated to be 5.6 eV. The second harmonic generation efficiency was calculated by the Kurtz and Perry powder method using a Q-switched mode locked Nd: YAG laser emitting 1064 nm laser as source. Finally, Z-scan technique was employed to determine the nonlinear refractive index, nonlinear absorption coefficient and third-order NLO susceptibility to find suitability of the grown crystal in photonics and optoelectronics applications. Keywords: Single crystal; Powder XRD; thermal analysis; SHG; Z-scan studies

Structural, Optical and Thermal Characterization of Synthesised Heterocyclic Organic Compound

A heterocyclic organic compound of 3-[(2z)-2-methyl-3-(4-nitrophenyl) prop-2-enoyl]-2H-(1-benzopyran-2-one) (MNB) is synthesized using Claisen-Schmidth condensation reaction. Structural characterization and presence of functional groups are carried out using powder X-ray diffractogram and FTIR spectroscopic studies respectively. Thermogravimetric analysis and differential thermal analysis are carried out to determine the melting property and it shows good thermal stability among organic crystal showing result at 166°C. Second Harmonic Generation efficiency study is carried out using Nd: YAG laser, this revealed that titled compound is good for NLO characterization and applicable in optoelectronics. PL wavelength present in visible region conclude that sample shows fluorescence property.

Investigation of polar crystalline materials containing hydrochlorothiazide: electron density distribution and optical properties

The polar hydrochlorothiazide polymorph (I) (systematic name: 6-chloro-1,1-dioxo-3,4-dihydro-2H-1,2,4-benzothiadiazine-7-sulfonamide, C7H8ClN3O4S2) and, recently designed by us, the polar 2-aminopyridine hydrochlorothiazide water <1/1/1> (C7H8ClN3O4S2·C5H6N2·H2O), (II), have been investigated. The crystal structures of both materials were determined using the single-crystal X-ray diffraction technique. The intermolecular interactions in (I) and (II) were studied in detail via topological electron-density analysis. The obtained results showed hydrogen bonds with a character intermediate between closed-shell and shared-shell in both crystal structures. The most important hydrogen bonds in (I) are formed between sulfonamide groups, whereas in (II), water molecules play a crucial role as they interconnect 2-aminopyridine and hydrochlorothiazide molecules. Calculations of the optical properties revealed that both materials exhibit large linear birefringence, twice that of calcite. The theoretically predicted second harmonic generation efficiency is four times and five times larger than that of KH2PO4 for (I) and (II), respectively. The information gathered on intermolecular interactions and structure–property correlations was used to identify the best strategies for the future design of new functional materials of this kind.

Harmonic generation with multi-layer dielectric metasurfaces

Metasurfaces have recently gained extensive interest because of their extraordinary optical behavior as artificial material interfaces with ultrahigh compactness. In this framework, dielectric platforms have newly become very promising for nonlinear nanophotonics, providing opportunities, especially for ultrafast optical switching, and high harmonic generation, opening the research field of nonlinear metaoptics. Up to now, nonlinear metaoptics have been mostly explored using single metasurfaces. However, in a long-term vision, the stacking of optical metasurfaces, very challenging in terms of fabrication, is one key goal of this research field. Here, we demonstrate a three-layer metasurface in the AlGaAs-on-insulator platform, which improves the second harmonic generation efficiency by more than one order of magnitude with respect to its one-layer counterpart. Our achievement paves the way toward phase-shaping multilayer and multifunctional all-dielectric metasurfaces.

Synthesis, crystal growth, characterization and DFT investigation of a nonlinear optically active cuminaldehyde derivative hydrazone

Single crystals of (E)-N′-(4-isopropylbenzylidene)isonicotinohydrazide monohydrate (IBIHM) were grown from ethanol by the slow evaporation from solution growth technique at room temperature. The structure was elucidated by single-crystal X-ray diffraction analysis and crystallized in the orthorhombic system with noncentrosymmetric space group P212121. Optical studies reveal that the absorption was minimum in the visible region and the band-gap energy was estimated using the Kubelka–Munk algorithm. The functional groups were identified by Fourier transform infrared spectral analysis. A scanning electron microscopy study revealed the surface morphology of the grown crystal. Investigation of the intermolecular interactions, crystal packing using Hirshfeld surface analysis and single-crystal X-ray diffraction confirm that the close contacts were associated with molecular interactions. Fingerprint plots of Hirshfeld surfaces are used to locate and analyze the percentage of hydrogen-bonding interactions. The second-harmonic generation efficiency of the grown specimen was superior to that of the reference material, potassium dihydrogen phosphate. The grown crystals were further characterized by mass spectrometry and elemental analysis. Theoretical studies using density functional theory (DFT) greatly substantiated the experimental observations. Large first-order molecular hyperpolarizability (β) of about ∼70× was observed for IBIHM. The efficiency of IBIHM in terms of nonlinear optical response was verified and the molecule displayed greater chemical stability and reactivity.

Doubly-Resonant Photonic Crystal Cavities for Efficient Second-Harmonic Generation in III–V Semiconductors

Second-order nonlinear effects, such as second-harmonic generation, can be strongly enhanced in nanofabricated photonic materials when both fundamental and harmonic frequencies are spatially and temporally confined. Practically designing low-volume and doubly-resonant nanoresonators in conventional semiconductor compounds is challenging owing to their intrinsic refractive index dispersion. In this work we review a recently developed strategy to design doubly-resonant nanocavities with low mode volume and large quality factor via localized defects in a photonic crystal structure. We built on this approach by applying an evolutionary optimization algorithm in connection with Maxwell equations solvers; the proposed design recipe can be applied to any material platform. We explicitly calculated the second-harmonic generation efficiency for doubly-resonant photonic crystal cavity designs in typical III–V semiconductor materials, such as GaN and AlGaAs, while targeting a fundamental harmonic at telecom wavelengths and fully accounting for the tensor nature of the respective nonlinear susceptibilities. These results may stimulate the realization of small footprint photonic nanostructures in leading semiconductor material platforms to achieve unprecedented nonlinear efficiencies.

Significantly enhanced second-harmonic generations with all-dielectric antenna array working in the quasi-bound states in the continuum and excited by linearly polarized plane waves

The recently emerging all-dielectric optical nanoantennas based on high-index semiconductors have proven to be an effective and low-loss alternative to metal-based plasmonic structures for light control and manipulations of light–matter interactions. Nonlinear optical effects have been widely investigated to employ the enhanced interactions between incident light and the dielectrics at the Mie-type resonances, and in particular magnetic dipole resonances, which are supported by the semiconductor. In this paper, we explore the novel phenomenon of bound states in the continuum supported by high-index semiconductor nanostructures. By carefully designing an array of nanodisk structures with an inner air slot as the defect, we show that a novel high quality-factor resonance achieved based on the concept of bound state in the continuum can be easily excited by the simplest linearly polarized plane wave at normal incidence. This resonance further enhances the interactions between light and semiconductors and boosts the nonlinear effects. Using AlGaAs as the nonlinear material, we demonstrate a significant increase in the second-harmonic generation efficiency, up to six orders of magnitude higher than that achieved by magnetic dipole resonances. In particular, a second-harmonic generation efficiency around 10% can be numerically achieved at a moderate incident pump intensity of 5 MW/cm2.

Enhancing second-harmonic generation with electron spill-out at metallic surfaces

Second-order nonlinear optical processes do not manifest in the bulk of centrosymmetric materials, but may occur in the angstroms-thick layer at surfaces. At such length scales, quantum mechanical effects come into play which could be crucial for an accurate description of plasmonic systems. In this article, we develop a theoretical model based on the quantum hydrodynamic description to study free-electron nonlinear dynamics in plasmonic systems. Our model predicts strong resonances induced by the spill-out of electron density at the metal surface. We show that these resonances can boost second-harmonic generation efficiency up to four orders of magnitude and can be arbitrarily tuned by controlling the electron spill-out at the metal surface with the aid of thin dielectric layers. These results offer a possibility to artificially increase nonlinear susceptibilities by engineering optical properties at the quantum level.

Growth, structural and optical properties of novel nonlinear optical potassium phthalate di lithium borate (KPDLiB) single crystals

Novel nonlinear optical semi-organic, potassium phthalate di lithium borate (KPDLiB) single crystals were successfully grown by the slow solvent evaporation technique. Good crystalline nature and an orthorhombic structure were confirmed by powder X-ray diffraction and single crystal X-ray diffraction studies. The functional groups of KPDLiB were identified using FT-IR spectrum recorded in the range of 4000 cm−1 to 450 cm−1. UV-Vis spectrum showed transmitting ability of the crystals in the entire visible region. The photoluminescence spectrum exhibited good fluorescence emission in a visible region at 384 nm, 416 nm and 578 nm. The second harmonic generation efficiency of the grown crystal was evaluated from Kurtz powder technique.