Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
13 results
Search Results
Item Z-scan and degenerate four wave mixing studies on newly synthesized copolymers containing alternating substituted thiophene and 1,3,4-oxadiazole units(2006) Kiran, A.J.; Udayakumar, D.; Chandrasekharan, K.; Vasudeva Adhikari, A.V.; Shashikala, H.D.The third-order nonlinear optical properties of newly synthesized copolymers containing alternating substituted thiophene and 1,3,4-oxadiazole units have been studied in DMF solution at 532 nm by using single beam Z-scan and degenerate four wave mixing techniques with nanosecond laser pulses. The variation of nonlinear response among the copolymers clearly indicates the dependence of ?(3) on donor and acceptor type of units present in the copolymers. The nonlinear refractive index, n2, of the investigated copolymers is found to be negative and the magnitude is as high as 10-10 esu. All samples exhibit strong reverse saturation absorption at the wavelength used and show good optical limiting of nanosecond pulses. The concentration dependence of n2 and the two-photon absorption coefficient (?) has been studied. © 2006 IOP Publishing Ltd.Item Nonlinear optical studies of 1-3-diaryl-propenones containing 4-methylthiophenyl moieties(2007) John Kiran, A.; Mithun, A.; Shivarama Holla, B.; Shashikala, H.D.; Umesh, G.; Chandrasekharan, K.The third-order nonlinear optical properties of chalcone derivatives have been studied using the single beam Z-scan technique. The dependence of ?(3) on different donor and acceptor type substituents demonstrates the electronic nonlinearity of compounds. The largest value of nonlinear refractive index, n2, measured for a high electron donor substituted molecule is -2.033 × 10-11 esu. These molecules exhibit a strong two-photon absorption and interesting optical limiting of nanosecond laser pulses at 532 nm. © 2006 Elsevier B.V. All rights reserved.Item Nonlinear optical studies of a newly synthesized copolymer containing oxadiazole and substituted thiophenes(2007) John Kiran, A.; Udayakumar, D.; Chandrasekharan, K.; Ahdikari, A.V.; Shashikala, H.D.; Philip, R.We investigated the third-order nonlinear optical properties of a newly synthesized soluble copolymer containing oxadiazole and thiophene units using Z-scan and Degenerate Four Wave Mixing (DFWM) techniques. The measurements were performed at 532 nm with 7 ns pulses from a Nd:YAG laser. We found a good agreement between the values of ?(3) determined from both experiments. Z-scan results indicate a negative nonlinear refractive index, n2, whose magnitude is of the order of 10-10 esu. The copolymer exhibits strong nonlinear absorption and good optical limiting properties at 532 nm, and hence may be a potential material for optical limiting applications. © 2006 Elsevier B.V. All rights reserved.Item Synthesis and nonlinear optical characterization of copolymers containing alternating 3,4-dialkoxythiophene and 1,3,4-oxadiazolydbenzene units(2007) Udayakumar, D.; Kiran, A.J.; Vasudeva Adhikari, A.V.; Chandrasekharan, K.; Shashikala, H.D.We report the synthesis and linear and third-order nonlinear optical (NLP) characterization of two novel copolymers containing alternating 3,4-dialkoxythiophene and 1,4-bis(1,3,4-oxadiazolyl)benzene units. The copolymers were synthesized with a precursor polyhydrazide route. Both copolymers exhibited fluorescence around 430 nm under the irradiation of UV light. The NLO measurements were made with the single-beam Z-scan technique with Nd:YAG nanosecond laser pulses at 532 nm. The nonlinear refractive index of the investigated copolymers was negative, and the magnitude was as high as 10 -10 esu. The samples exhibited strong reverse saturation absorption and very good optical limiting properties at the wavelength used. The concentration dependence of third-order NLO parameters was studied. ©2007 Wiley Periodicals, Inc.Item Nonlinear optical properties of p-(N,N-dimethylamino)dibenzylideneacetone doped polymer(2008) Kiran, A.J.; Satheesh Rai, N.; Udayakumar, D.; Chandrasekharan, K.; Kalluraya, B.; Philip, R.; Shashikala, H.D.; Vasudeva Adhikari, A.V.A bis-chalcone derivative, p-(N,N-dimethylamino) dibenzylideneacetone was synthesized. Its third-order nonlinear susceptibility was determined to be as high as 10-12 esu by employing single beam Z-scan and degenerate four wave mixing techniques using Nd:YAG 7 ns laser pulses at 532 nm. The compound was doped in to poly(methylmethacrylate) matrix and the third-order nonlinearity was investigated by using Z-scan technique. The nonlinear refractive index of the doped polymer is found to be negative, and its magnitude is of the order of 10-10 esu. The results show that the compound exhibits strong reverse saturable absorption and a good optical limiting property and hence may be used as a promising dopant material. The study on concentration dependence of nonlinear optical parameters has been presented. © 2007 Elsevier Ltd. All rights reserved.Item Optical and mechanical properties of calcium phosphate glasses(Maik Nauka Publishing / Springer SBM compmg@maik.ru, 2014) Venkateswara Rao, G.V.; Shashikala, H.D.Binary calcium phosphate glasses in the system, xCaO-(100 - x) P 2O5 with x = 30, 35, 40, 45, and 50 mol % were prepared by conventional melt quenching technique. The density, molar volume and refractive index of the glasses were found to increase with the increase in CaO content. Structural investigation by FTIR spectroscopy revealed that the substitution of P2O5 by CaO depolymerizes the phosphate glass network by systematic conversion of Q3 structural units to Q2 structural units by breaking the P-O-P links. From the optical absorption studies, the optical band gap values were found to decrease with increasing CaO content which can be due to increase in the concentration of non-bridging oxygens in the glass network. Vickers hardness increased with the calcium oxide content due to densification. The fracture toughness decreases with the increase in CaO content due to the increase in the bond density between the modifying cations and the non-bridging oxygens in the glass network. It was observed that brittleness increases with the addition of CaO content which can be mainly attributed to the decrease in the molar volume. © 2014 Pleiades Publishing, Ltd.Item Structural, optical and mechanical properties of ternary CaO-CaF2-P2O5 glasses(Tsinghua University, 2014) Venkateswara Rao, G.V.; Shashikala, H.D.The ternary phosphate glass series (50?x)CaO-xCaF2-50P2O5 (x = 0–20 mol%) were synthesized using melt quench technique. Structural, optical and mechanical properties were investigated with increase in CaF2 content. Using X-ray diffraction (XRD), synthesized glasses were confirmed to be amorphous in nature. Replacement of oxygen ions by fluorine ions increased the values of density. Decrease in refractive index due to the low polarizability of fluorine ions in the glass matrix was observed. In Fourier transform infrared (FTIR) spectra, the slight variation in ?as (PO2) band position and intensity could be attributed to replacement of fluorine ions for oxygen ions in phosphate glass structure. These data were well supported by Raman spectra. Optical band gap energy increased from 3.44 eV to 3.64 eV with increase in CaF2 content, and Urbach energy decreased suggesting that the fluorine ions reduced the tail energy states in the band gap compared to the oxygen ions. Mechanical parameters such as Vickers hardness, fracture toughness and brittleness were evaluated from the Vickers micro indentation measurements. Increase in Vickers hardness, decrease in fracture toughness and increase in brittleness were observed with increase in CaF2 content. © 2014, The Author(s).Item Statistical optimization of melt-quenching process parameters for multiple properties of ternary barium phosphate glasses(Elsevier Ltd, 2015) Narayanan, M.K.; Shashikala, H.D.; Manjaiah, M.In the present work simultaneous optimization of density, refractive index and hardness (multiple performance characteristics) of ternary barium phosphate glasses has been carried out using Taguchi based grey relational analysis. Effect of the parameters such as CaF2 content, melting temperature and melting time on the response parameters of (50 - X)BaO-XCaF2-50P2O5 (X = 0, 10, 20 mol%) glasses prepared according to the experimental layout of Taguchi's standard orthogonal array has been studied. Highest grey relational grade is the performance criteria used in this study to indicate the optimum level of process parameters needed for the best multiple performance characteristics. Analysis of variance (ANOVA) conducted on grey relational grade shows that under 95% confidence level, CaF2 content is the only parameter significantly affecting multiple performance characteristics. Experimental values of response parameters obtained by conducting the confirmatory experiment at optimum level of process parameters are closer to the optimal set of predicted values. © 2014 Elsevier B.V. All rights reserved.Item Thermal and optical properties of BaO-CaF2-P2O5 glasses(Elsevier B.V., 2015) Narayanan, M.K.; Shashikala, H.D.Thermal and optical properties of ternary phosphate glasses prepared by conventional melt-quenching technique, belonging to the series (50 - X)BaO-XCaF2-50P2O5 (X = 0 to 10 mol%) were investigated with increase in CaF2 content. Thermal stability and glass forming ability studied using differential thermal analysis (DTA) were found to increase with the increase in CaF2 content. Powder X-ray diffraction (XRD) analysis of heat treated samples also revealed that CaF2 addition improves the thermal stability against crystallization. Increase in both glass transition temperature and onset crystallization temperature with the increase in CaF2 content can be attributed to the partial substitution of Ba2 + ion with Ca2 + ion, which is having larger field strength. The observed decrease in the melting temperature of glass batch with the increase in CaF2 content indicates that CaF2 acts as a flux and reduces the viscosity of the glass melt. The decrease in refractive index of the glasses with the increase in CaF2 content can be attributed to replacement of lower field strength Ba2 + by Ca2 + or the partial substitution of more polarizable oxygen ion by fluorine. Optical band gap energy slightly increased and Urbach energy marginally reduced with the increase in CaF2 content. Increase in optical band gap energy was further confirmed by calculating theoretical optical basicity of glasses. Average anion polarizability (?O/F) of (50 - X)BaO-XCaF2-50P2O5 glasses calculated from refractivity data using Lorentz-Lorentz relation was correlated with its theoretical optical basicity (?th) using the previously established correlation for oxyfluoro phosphate glasses. © 2015 Elsevier B.V. All rights reserved.Item Influence of Fe3+ ions on optical, structural, thermal and mechanical properties of Li2O–Na2O–K2O–ZnO–B2O3 based glass system(Elsevier Ltd, 2020) Subhashini, u.; Shashikala, H.D.; Udayashankar, N.K.The effect of addition of Fe3+ ions in Li2O–Na2O–K2O–ZnO–B2O3 based glass system have been studied. The melt quenching technique is used to prepare the glass samples. The X-ray diffraction studies confirmed the amorphous nature of the samples. DSC thermographs indicate that the Tg is decreasing as the addition of Fe2O3 content. Increase in thermal stability is observed upon adding K2O to the F0 sample and increase in the Fe2O3 content further enhanced the thermal stability up to 187 °C. Optical band gap energy (Eg) of the studied glass system is found to reduce with increasing Fe2O3 content. A band observed around 450 nm in UV absorption spectra is due to the d-d transition of 6A1g(S) ? 4T2g(G) which indicates the presence of iron ion in trivalent state (Fe3+) with distorted octahedral symmetry. The oxide ion polarizability values determined using the refractive index and optical band gap energy are found to be increasing monotonically with partial incorporation of K2O content and with increasing Fe2O3 content. The FTIR and Raman spectroscopy studies confirmed the network modifier role of Fe2O3. The radial-median cracks produced due to Vickers indentation were studied and it confirmed the enhancement in brittleness of the samples as Fe2O3 content increased. Further efforts have been made to analyse and establish correlation between the physical and mechanical properties with the structural modification of the studied glass system. © 2019 Elsevier Ltd and Techna Group S.r.l.