Papers by Keyword: Second Harmonic Generation

Abstract: We investigated the change of optical second harmonic generation (SHG) intensity during In/Si (111) interface formation. It was proved that Si (111)2×2-In reconstruction is formed by one monolayer of In on silicon surface.

Abstract: The system of achromatic phase matching (APM) based on grating pairs is designed by the commercial optical design software ZEMAX. Firstly, we theoretically calculate the theoretical incident angular where each frequency components exactly reaches the phase-matching in nonlinear crystals. Subsequently, the model of APM system is built and optimized in ZEMAX. The results are well in accordance with the theoretical ones. In addition, the effects of grating frequency and aberration produced by the focus lens on APM scheme are analyzed.

Abstract: Hybrid organic-inorganic films are attractive materials for an alternative manufacture of photonic devices based on non-linear second-order optical processes. However, their efficiency and stability, closely related to their chromophores non-centrosymmetric orientation, still need some improvements. The use of nanostructures in this kind of materials gives place to a change in the chromophores surrounding medium; it can be used to improve the efficiency and the stability of the chromophores orientation in the films. In this work we show that some nanostructures are able to improve significantly the organic-inorganic SiO₂ films second-order non-linear optical responses. Two kinds of nanostructures were studied: some nanostructures were just immersed, but the other ones were spontaneously induced in the films. The immersed nanostructures were multi-walled carbon nanotubes and the spontaneously induced nanostructures were formed in the films by means of surfactants self-assembly. The films were synthesized by the sol-gel method and all of the films were doped with Disperse Red 1 (DR1) dipolar chromophores. The induced nanostructures were lamellar and hexagonal long-range ordered nanostructures, detected by X-ray diffraction (XRD). The second-order non-linear optical properties of the films were studied in resonance through Corona poling assisted second harmonic generation. The results show significant improvements, for some kinds of nanostructures, in the non-linear optical responses of the films. In particular, those films containing Triton X-100 showed, at a poling temperature of 120°C, an improved second-order non-linear coefficient d₃₃ with respect to equivalent non-nanostructured films; the d₃₃ value of those films, determined by the Maker fringes technique, was equal to 21.4 pm/V.

Abstract: Although second harmonic generations from gold- and copper-nanowires have been the subject of extensive studies, a complete understanding of the mechanism of the enhancement is still missing. The aim of review article is to address these issues by performing systemic studies of mechanism of the resonant enhancements between gold- and copper-nanowires in terms of surface reconstruction and relativistic effect, and implements these types of candidate for the potential applications in optical communications and optical devices.

Abstract: The second-order responses depend on the structural symmetry of the metal nanostructures, which can give rise to interesting polarization dependences in the responses. We also show that the sensitivity of second-order processes to the symmetry provides important information about plasmonic effects in the nonlinear properties of the structures.

Abstract: The crystal structure of N-[2,4,5-Trichlorophenyl] acetamide is optimized through semi-empirical method by Austin Model 1 (AM1) together with restricted Hartree-Fock closed shell wave function to describe the influence of interactions on crystal packing using MOPAC2009 program. The electric dipole moment (μ)and molecular hyperpolarizabilities (β and γ)are computedbytime dependent Hartree Fock (TDHF) method to inspect the non-linear optical behaviour of the material. The UV-VIS spectral study of material in 300-1100 nm wavelength range shows a wide transparency window which is the key requirement for the non-linear optical (NLO) property of the material. The experimentally measured value of second harmonic generation efficiency is 0.8 times to that of reference material potassium dihydrogen phosphate (KDP). The intramolecular charge transfer interaction results during the HOMO-LUMO transition observed from molecular orbital calculations.

Abstract: The strongly geometrical shape, high aspect ratios, and nanoscale cross-section of nanowires is expected to affect optical properties through confinement effects. Herein we have investigated optical properties of Cu nanowires with studies of second harmonic generation (SHG) spectra. These optical properties of Cu nanowires will be one of the most important issues when considering the types of materials used in current applications and development of new applications.

Abstract: L- Histidinium Perchlorate, a semi organic nonlinear optical material was grown by solution growth method. The absorption studies show minimum absorption in the entire visible region. The optical band gap (Eg) value of the grown crystal is obtained from the tauc’s plot of (αhν)2 vs hν which was determined by extrapolating the linear region of the curve to the hν axis where (αhν)2=0. Furthermore linear optical parameters such as Extinction coefficient, Reflectance, Refractive index, Complex dielectric constant and Optical conductivity are calculated and its variation with incident photon energy is analyzed. Second Harmonic Generating (SHG) efficiency of the candidate material was determined by Nd:YAG Q-switched laser Kurtz powder techinqe and its 3.19 times greater than KDP.

Abstract: Click chemistry is used for synthesizing polymers for second order NLO study. The molecular weights found by gel-permeation chromatography (GPC), were in the range of 7000-55000 g/mol. Differential scanning calorimetry shows glass transition temperature (Tg) above 120 oC. From electronic spectra order parameter of the poled films were calculated to be 0.1-0.5. The change in surface morphology after poling was checked by atomic force microscopy. By using a pulsed Nd:YAG laser (1064nm), the second harmonic generation (SHG) intensity was measured. The SHG intensity was also studied as a function of against temperature and time respectively.

Abstract: Novel concepts of nonlinear-optical (NLO) photonic metamaterial are proposed. They concern photonic materials that support backward electromagnetic or vibration waves (BWs) and provide coherent nonlinear-optical energy exchange between ordinary and BWs as applied to three- and four-wave mixing processes. Three different classes of materials which support BWs are considered: plasmonic negative-index (NI) metamaterials (NIMs), metamaterials with specially engineered spatial dispersion of the nanoscopic building blocks, such as standing carbon nanotubes, and crystals that support optical phonons with negative group velocity. The possibility to exploit ordinary crystals instead of plasmonic NLO metamaterials that are very challenging to engineer is proposed. It is shown that extraordinary nonlinear optical frequency-conversion propagation processes attributed to NIMs can be mimicked in the proposed metamaterials. It is also shown that the detrimental effects of strong losses can be mitigated in the short-pulse regimes, which exhibit exotic properties when ordinary and BWs are involved in the NLO coupling. Comparative review of unparallel properties of coherent energy exchange between ordinary and backward electromagnetic waves in NIMs and between ordinary electromagnetic waves coupled through backward vibration waves is given. Unique photonic devices are proposed.