G. Vinitha

Improved third-order optical nonlinearity and optical limiting behaviour of (nanospindle and nanosphere) zinc ferrite decorated reduced graphene oxide under continuous and ultrafast laser excitation

Nanohybrids consisting of uniform nanospheres and nanospindles of zinc ferrite attached to reduced graphene oxide were prepared by hydrothermal reaction. Zinc ferrite decorated reduced graphene oxide exhibited enhanced nonlinear absorption, refraction and optical limiting (OL) action under continuous wave (532 nm, 50 mW) and ultrafast (800 nm, 150 fs) excitation. The enhancement can possibly be attributed to the synergistic effect stemming from the observed reverse saturable absorption and self-defocusing in the material. The role of defects in improving the nonlinear optical (NLO) performance of ZnFe2O4–rGO was explained with the aid of Raman spectroscopy and ground state absorption studies. Using fs and cw excitation, the estimated nonlinear absorption coefficient [γ3PA(fs) = 4.0 × 10−12 m W−1, β(cw) = 6.5 × 10−5 m W−1], nonlinear refractive index [n2(fs) = 4.2 × 10−18 m2 W−1, n2(cw) = 4.7 × 10−12 m2 W−1] and third order nonlinear optical (NLO) susceptibility [χ (3) (fs) = 1.9 × 10−15 esu, χ (3) (cw) = 4.2 × 10−6 esu] of nanospindle ZnFe2O4–rGO were found to be higher than those of its other counter parts. The estimated NLO parameters were found to be higher than those of other known OL materials such as functionalized hydrogen exfoliated graphene, CdO. Thus zinc ferrite decorated rGO nanostructures with proficient NLO coefficients have potential scope for utilizing them as smart materials for OL applications.

Ethylenediaminium di(4-nitrophenolate): A third order NLO material for optical limiting applications

Single crystals of ethylenediaminium di(4-nitrophenolate) [EDA4NP] were grown by slow evaporation solution growth technique using ethanol as solvent at constant temperature. It crystallizes in monoclinic centrosymmetric space group C2/c with cell dimension a=11.326Ǻ, b=7.264Ǻ, c=20.036Ǻ; β=93.55°. Fourier Transform Infra Red (FT-IR) spectrum was recorded to identify various functional groups present in EDA4NP. Nuclear Magnetic Resonance (NMR) spectral studies were performed to confirm the functional groups. Thermogravimetric analysis and differential thermal analysis showed that the compound melts at 142.9°C. The material possesses a wide optical transparency window in the visible and near IR region (500-1200nm). The nonlinear refractive index, nonlinear absorption coefficient and third-order nonlinear susceptibility of EDA4NP were estimated to be n2=5.46×10(-8)cm(2)W(-1), β=0.65×10(-3)cmW(-1) and χ((3))=2.96×10(-6)esu respectively. The limiting behavior observed with the sample is attributed mainly to nonlinear refraction.

Low power optical limiting studies of copper doped lithium tetraborate nanoparticles.

The copper doped lithium tetraborate (LTB:Cu) nanoparticles were synthesized by sol-gel method and characterized by XRD (tetragonal structure) and by FESEM (sphere-like nanoparticle). UV-Vis studies show that there is no strong absorption in the visible region. In the luminescence spectrum, the emission peak at 370 nm reveals the presence of Cu+ in LTB lattice. The relative powder second harmonic generation efficiency of pure and doped LTB is equal to the standard NLO material, KDP. The nonlinear optical parameters of LTB:Cu nanoparticles say, nonlinear refractive index, nonlinear absorption coefficient and third order nonlinear optical susceptibility were determined to be of the order of 10(-8)cm2/W, 10(-2) cm/W and 10(-5) esu, respectively. The optical power limiting behavior of the samples were studied by Z-scan technique with (532 nm, 50 mW) Nd:YAG laser and the limiting threshold values are found to be 22.7 mW for 0.01 M and 24.9 mW for 0.03 and 0.05 M LTB:Cu nanoparticles.

χ(3) measurement and optical power limiting behavior of manganese doped lithium tetraborate nanoparticles

Manganese doped Li2B4O7 nano crystallites were prepared by chemical method and characterized by XRD, FTIR, UV and fluorescence spectra. FESEM reveals that the particles are coagulated and the particle size is in the range of 50-107 nm. Bands appear at 682-769 cm(-1) corresponds to the bending of B-O linkage in borate network. Nonradiative energy transfer process is observed from fluorescence spectrum. UV-Vis studies show the samples are completely transparent in the visible region and having absorption peaks (234 and 276 nm) in UV regime. The measured second harmonic generation values are 0.9 times KDP. The nonlinear optical parameters such as nonlinear refractive index, n2 (10(-8) cm(2)/W), nonlinear absorption, β (10(-2) cm/W) and nonlinear optical susceptibility, χ(3) (10(-5) esu) are estimated using a Nd:YAG laser (532 nm, 50 mW).

Crystal structure, molecular packing, FMO, NBO, nonlinear optical and optical limiting properties of an organic imidazolium diphenylacetate diphenylacetic acid single crystal

An organic nonlinear optical (NLO) crystal, imidazolium diphenylacetate diphenylacetic acid (IDA), was synthesized and grown by the slow evaporation method. Formation of the new crystalline compound was confirmed by single crystal X-ray diffraction study. The title compound crystallizes in the triclinic crystal system with the space group P. UV-vis-NIR spectral study showed that the grown crystal is transparent in the entire visible region with a lower cut-off wavelength of 275 nm. Density functional theory (DFT) calculations were carried out to calculate the frontier molecular orbitals and natural bonding orbitals of the IDA compound. The frontier energy gaps calculated theoretically were useful to understand the charge transfer taking place in the molecule. The natural bonding orbital analysis provides a convenient basis for the investigation of the charge transfer or conjugative interactions in the molecular system. Vickers microhardness study revealed that the title material belongs to the soft material category. The values of fracture toughness, brittleness index and yield strength have also been calculated for Palmqvist and median types of cracks. The title compound IDA is thermally stable up to 201 °C, as assessed by thermogravimetric and differential thermal (TG-DTA) analyses. The specific heat capacity of IDA is found to be 3.25 J kg−1 K−1 at 65 °C. The laser induced surface damage threshold of the grown crystal was measured to be 0.2645 GW cm−2 with 1064 nm Nd:YAG laser radiation. The nonlinear refractive index (n2), absorption coefficient (β) and third order nonlinear susceptibility (χ(3)) were determined using the Z-scan technique. An optical limiting study revealed that the transmitted output power increases linearly with the input power up to an irradiance of around 3.6 mW cm−2.

Low Power Optical Limiting Behavior of Graphene Oxide

The third order NLO properties of dispersed graphene oxide (GO) was measured using a Nd:YAG laser (532nm, 50mW) . The material possesses negative nonlinearity and self defocusing nature which is responsible for the optical limiting behavior in the regime of interest.