Showing papers by "T.C. Sabari Girisun published in 2017"

Super-paramagnetic and unusual nonlinear absorption switching behavior of an in situ decorated CdFe2O4–rGO nanocomposite

Abstract: A simple strategy based on electrostatic interaction was utilized to assemble in situ cadmium ferrite of various morphologies (nanoplatelets to nanorods) on reduced graphene oxide sheets using a one-step hydrothermal reaction. With ultrafast laser excitation (800 nm, 150 fs and 80 MHz), intensity dependent open aperture Z-scan data confirmed the presence of nonlinear absorption in pure GO [saturable absorption] and CdFe2O4 [reverse saturable absorption]. Surprisingly, the nanocomposite exhibited unusual switching of reverse saturable absorption at low peak intensities (I0 = 150 MW cm−2) to saturable absorption behavior at high peak intensities (I0 = 250 MW cm−2 and 350 MW cm−2). This unusual nonlinear absorption switching suggests the contribution of the individual components of the nanocomposite with respect to the intensity of excitation. All the samples exhibited nonlinear self-defocusing behaviour resulting from thermally-induced nonlinear refraction. High NLO coefficients were observed for the CdFe2O4− (15 wt%) rGO nanocomposite which can be attributed to the synergetic effects stemming from the extent of conjugation with the graphene layers and 1D nanostructures of cadmium ferrite with a large reactive surface area for optical excitations. Earlier the different loadings and their respective morphologies were investigated by XPS, Raman, TGA, FESEM and TEM studies. Furthermore, the alteration in ground-state absorption and superparamagnetic properties with trimming was also analysed. Tunability of the thermal, magnetic, linear optical and NLO properties of the composites arises mainly due to tailoring the proportion of oxygen containing groups in the graphene layer and the CdFe2O4 loading on the graphene sheets, and the morphology of the CdFe2O4·CdFe2O4− (15 wt%) rGO nanocomposite exhibits excellent optical limiting action, implying the potential possibility of it being used in laser safety devices.

Variable ultrafast optical nonlinearity in bacteriorhodopsin achieved through simple chemical treatment

Abstract: Tunability of the third-order optical nonlinearity and optical limiting action of bacteriorhodopsin (BR) was achieved by altering the native structure through simple surfactant treatment like cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and Triton X-100. The variation in spectral position and intensity of the UV–visible absorption spectrum was due to aggregation (hyperchromic lipid absorption—280 nm), solubilization (redshift in chromophore absorption—600 nm, formation of retinal—396 nm) and monomerization (blueshift in chromophore absorption—553 nm) effects upon interaction with anionic, cationic and non-ionic surfactants. Further, changes in the Raman vibrational modes confirmed the alteration in C=C ethylenic chain and 13-cis retinal on surfactant treatment. Surfactant dose-dependent assay of nonlinear optical parameters was evaluated by using the Z-scan technique with ultrashort laser pulse excitation (800 nm, ~150 fs, 80 MHz). The closed aperture data demonstrated self-defocusing nature and notably higher monomerization (0.15–0.25 mM) effects endorsed sign reversal (self-defocusing to self-focusing) of the nonlinear refractive index coefficient. Bare BR exhibited saturable absorption, while reverse saturable absorption (RSA) was observed for all surfactant-treated samples (expect for 0.20 mM CTAB and 1.0 mM SDS). The observed RSA and optical limiting was ascribed due to two-photon absorption process. Interestingly, we observed that aggregation enhanced the nonlinear refraction, monomerization improved nonlinear absorption (NLA), and solubilization reduced the nonlinear optical (NLO) response of BR. The maximum nonlinear refractive index (n 2 = 8.78 × 10−19 m2/W) was observed for 0.20 mM CTAB, while the NLA coefficient (β = 4.40 × 10−12 m/W) and low optical limiting threshold (538 µJ/cm2) were observed to be highest for 0.25 mM TX-100 sample. The influence of aggregation, monomerization and solubilization effects of purple membrane in achieving the variation of the NLO coefficients is discussed.

Nonlinear Absorption and Limiting Behaviour of Monoclinic and Orthorhombic Copper Niobate

Abstract: Monoclinic and orthorhombic phase of copper niobate was prepared by simple solid state reaction (700°C, 900°C for 12 hours) Formation of two polymorphic phases of CuNb2O6 was ascertained by XRD and FTIR analysis FESEM showed the presence of pore networks in both phases Third-order optical nonlinearity and their limiting behaviour were studied by Z-scan technique using Ti: Sapphire laser (800 nm, 150 fs, 80 MHz) Both phases of copper niobate exhibit reverse saturable absorption The observed optical limiting action was ascribed due to two-photon absorption process Monoclinic copper niobate shows almost 100 times stronger nonlinear absorption behaviour than orthorhombic copper niobate due to peculiar distortion of NbO6 octahedra Monoclinic copper niobate with high two photon absorption coefficient (85x10-10 m/W) and low limiting threshold (021 μJ/cm2) can be a better alternate for benchmark optical limiters like carbon nanotubes

Nonlinear Optical Behavior of Nanostructured 4-Dimethyl-Aminopyridinium Dihydrogen Phosphate

Abstract: Optical nonlinearity of 4-dimethyl aminopyridinium dihydrogen phosphate (DMAPDP) was studied using continuous wave of diode pumped Nd:YAG laser (532nm, 50mW). The nonlinear refractive index, nonlinear absorption coefficient and nonlinear optical (NLO) susceptibility of the sample were found to be in the order of 10−8cm2/W, 10−3cm/W and 10−6 esu respectively. The observed self defocusing effect was used to demonstrate the optical limiting action at 532nm. Initially, XRD analysis showed that DMAPDP crystallizes in triclinic crystal system with centrosymmetric space group P1¯. Thermal studies explored that the material undergoes an irreversible endothermic transition at 192∘C which correspond to the decomposition of material. SEM image portrays the formation of nanoparticles with grain size in the range of 45–170nm. Hence 4-dimethyl aminopyridinium dihydrogen phosphate nanoparticles can be used as potential candidate for optical limiting applications.