Papers by Keyword: Nonlinear Optics (NLO)

Abstract: We demonstrate that bilayer graphene exhibits strong nonlinear optical response in the terahertz frequency regime. The electric field strength required to generate single-frequency and triple-frequency nonlinear optical responses comparable to the linear optical response is only moderate and can be easily achieved in laboratory. This strong nonlinear optical response persists even in room temperature. This suggests that bilayer graphene can potentially be utilized in nonlinear terahertz photonics.

Abstract: 1.2μm – laser pumped wide frequency tunable coherent terahertz (THz) light source is demonstrated. The operation principle is based on difference frequency generation (DFG) with an excitation of phonon – polariton in Gallium Selenide (GaSe) crystal. The pump and signal lasers used are 1.2μm Cr:Forsterite lasers. The tuning range of the THz wave frequency covers from 0.3THz to 4.8THz (type eoo phase matching) and 8.3THz to 10.2THz (type eoo phase matching) under collinear phase matching conditions. It is shown that the maximum conversion efficiency is up to ~10^-6, which is 3 orders in magnitude larger than that of Gallium Phosphide (GaP) crystal.

Abstract: The synthesis of a suite of compounds containing three chromophores coupled to a central nitrogen atom are reported. X-ray crystallographic data has been obtained for two of the compounds and this suggests that incorporation of these molecules into such a trichomophore bundle is a valid strategy for minimizing dipole-dipole interactions, and therefore aggregation in these compounds.

Abstract: Measurements of nonlinear optical properties of a newly synthesized thiophene based polymer are reported. The nonlinear transmission measurements were performed on the polymer dissolved in N,N-dimethylformamide by employing the single beam Z-scan technique using a Q-switched laser output at 532-nm. The polymer shows strong optical limiting behavior, where the transmittance decreases when the pump fluence is increased. It was found that an effective three-photon absorption (3PA) model at the excitation wavelength gives the best fit to the obtained experimental data. The value of the 3PA coefficient has been numerically calculated. This study clearly reveals the potential of new polymeric material has, for optical limiting applications.

Abstract: Compounds 1 were synthesized, in good to excellent yields (72-87%), through condensation of formyl-arylthiophene precursors 2 with 1,2-diaminoanthraquinone in ethanol at reflux, followed by cyclisation of the imine intermediate with Pb(OAc)4 in acetic acid at room temperature. Evaluation of the thermal, linear and NLO properties of these compounds was carried out. The  values of chromophores 1, measured by hyper-Rayleigh scattering (HRS) technique, are several times larger (49-67) than that of the standard reference molecule p-nitroaniline (pNA). Due to their excellent thermal stability, (Td = 341-446 oC), and good NLO properties, arylthienyl-imidazo-anthraquinones 1 could be used as new efficient and thermally stable NLO materials.

Abstract: New push-pull thiobarbituric (oligo)thiophene derivatives 1 were synthesized, in good to excellent yields (60-98%), through Knoevenagel condensation of the corresponding formyl-(oligo)thiophenes 2 with 1,3-diethylthiobarbituric acid in dichloromethane, under basic conditions. Evaluation of the thermal and solvatochromic properties of these compounds was carried out and their NLO response was estimated. The values obtained suggest that these (oligo)thiophenes have good potential to be used as novel NLO materials.

Abstract: Li(Ga1-xMx)O2 (M: B or Al) single crystals are grown by Floating zone method. These crystals are characterized from the viewpoint of the substitution of M, such as lattice parameter (lattice volume) change, piezoelectric properties and nonlinear optics. The lattice volume is decreased with the increase of Al content for Al-substitution largely, but the change is a little for B-substitution.

Abstract: We review our progress in developing single-mode tellurite glass holey fiber for infrared nonlinear applications. Tellurite glass preforms with complex holey structure were fabricated by using glass extrusion technique. The fabrication of single-mode tellurite holey fibers with the effective mode area ranging from 2.6-3000mm2 and the effective nonlinearity γ ranging from 0.23- 280W-1km-1 were demonstrated. By controlling the microstructured features in the holey cladding, the dispersion profile and the zero dispersion wavelength of this type of single-material optical fiber were tailored within a broad range. Broadband supercontinuum spectra from 0.9 to 2.5mm were generated from the fabricated fibers by using femtosecond laser. Attenuations due to the impurities, such as transition metal ions, rare-earth ions and hydroxyl groups, were also investigated in the bulk tellurite glass and fiber from visible to mid-infrared regimes.

Abstract: Applying a bicolor coherent treatment of a Nd-YAG laser with wavelength 1.32 μm and its second harmonic generation, we have investigated photoinduced SHG in Au nanoparticledeposited ZnO nanocrystallinne (NC) films. We have established that coexistence of the such crystallites gives substantially better results compared to the pure ZnO NC deposited onto the glass substrate. It was shown that the value of the second order susceptibility obtained for the large incident angles of the fundamental and writing beams is equal to about 23 pm/V. The better results are obtained during the phototreatment at temperatures near the 60 oC for the Au doped samples and is almost non-sensitive to temperature for the pure samples. The further increase of the temperature leads to decay of the optical second harmonic generation

Abstract: The synthesis of 5-arylazo- substituted bithiophenes and their UV-visible, solvatochromic and nonlinear optical properties (NLO) are described. In agreement with the solvatochromic data and also with the second-order molecular NLO characterization, the new donor-acceptor systems could find application as suitable solvatochromic probes and also as new NLO materials.