Faculty Publications
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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 Third-order nonlinear optical studies of newly synthesized polyoxadiazoles containing 3,4-dialkoxythiophenes(2006) Udayakumar, D.; John Kiran, A.; Vasudeva Adhikari, A.V.; Chandrasekharan, K.; Umesh, G.; Shashikala, H.D.The third-order nonlinear optical properties of newly synthesized soluble polyoxadiazoles containing 3,4-dialkoxythiophenes were investigated by 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 the experiments. Z-scan results indicate a negative nonlinear refractive index, n2, whose magnitude is of the order of 10-10 esu for all the copolymers. The variation of nonlinear response among the copolymers clearly indicates the dependence of ?(3) on donor and acceptor type of units present in these copolymers. The copolymers exhibit strong reverse saturable absorption and good optical limiting properties at 532 nm. © 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 Third-order nonlinear optical susceptibilities of new copolymers containing alternate 3,4-dialkoxythiophene and (1,3,4-oxadiazolyl)pyridine moieties(Elsevier, 2009) Hegde, P.K.; Vasudeva Adhikari, A.V.; Manjunatha, M.G.; Poornesh, P.; Umesh, G.A new series of conjugated copolymers (P1-P3) consisting of alternate 3,4-dialkoxythiophene and (1,3,4-oxadiazolyl)pyridine moieties have been synthesized using the precursor polyhydrazide route. They have been characterized by FTIR, 1H NMR spectral and elemental analyses. These copolymers possess well defined structure and exhibit good thermal stability with the onset decomposition temperature in nitrogen at around 300 °C. Their molecular weights were determined by gel permeation chromatography (GPC). The optical and charge-transporting properties of the copolymers were investigated by UV-visible spectroscopy, fluorescence emission spectroscopy and cyclic voltammetry. Their UV-visible absorption spectra showed a ?max at around 342 nm and displayed bluish-green fluorescence in solution state. The band gaps were found to be at about 2.55 eV for all the copolymers. The third-order nonlinear optical properties (NLO) of these copolymers were studied by Z-scan technique. The measurements were performed at 532 nm with 7 ns laser pulses using a Nd:YAG laser in solution form. The real part of ?(3) were estimated to be -0.881 × 10-12, -0.901 × 10-12 and -1.030 × 10-12 esu for P1, P2 and P3 respectively. The imaginary part of ?(3) for the copolymers P1, P2 and P3 were determined to be 0.192 × 10-12, 0.253 × 10-12 and 0.272 × 10-12 esu respectively. The copolymers exhibit strong reverse saturable absorption and good optical limiting behaviour at 532 nm. © 2008 Elsevier B.V. All rights reserved.Item Studies on third-order nonlinear optical properties and reverse saturable absorption in polythiophene/poly (methylmethacrylate) composites(Springer Verlag, 2009) Poornesh, P.; Umesh, G.; Hegde, P.K.; Manjunatha, M.G.; Manjunatha, K.B.; Vasudeva Adhikari, A.V.We report here the studies on third-order nonlinear optical properties of two novel polythiophene composite films investigated using the Z-scan technique. The measurements were carried out using a Q-switched, frequency doubled Nd:YAG laser producing 7 nanosecond laser pulses at 532 nm. Z-scan results reveal that the composite films exhibit self-defocusing nonlinearity. The real and imaginary parts of the third-order nonlinear optical susceptibility were of the order 10-12 esu. The effective excited-state absorption cross section was found to be larger than the ground state absorption cross section, indicating that the operating nonlinear mechanism is reverse saturable absorption (RSA). The polythiophene composite films also exhibit good optical power limiting of the nanosecond laser pulses. The nonlinear optical parameters are found to increase on increasing the strength of the electron-donor group, indicating the dependence of ? (3) on the electron-donor/acceptor units of polythiophenes. © 2009 Springer-Verlag.Item Nonlinear optical studies on a new poly{2-(biphenyl-4-yl)-5-[3,4- didecyloxy-5-(1,3,4-oxadiazol-2-yl)thiophen-2-yl]-1,3,4-oxadiazole}(Trans Tech Publications Ltd ttp@transtec.ch, 2010) Hegde, P.K.; Vasudeva Adhikari, A.V.; Manjunatha, M.G.; Suchand Sandeep, C.S.; Philip, R.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. © (2010) Trans Tech Publications.Item Nonlinear optical and optical power limiting studies on a new thiophene-based conjugated polymer in solution and solid PMMA matrix(2010) Poornesh, P.; Hegde, P.K.; Umesh, G.; Manjunatha, M.G.; Manjunatha, K.B.; Vasudeva Adhikari, A.V.An experimental investigation of the third-order nonlinear optical properties of new poly{2-{5-[3,4-ditetradecyloxy-5-(1,3,4-oxadiazol-2-yl)thiophen-2-yl]-1,3,4-oxadiazol-2-yl}pyridine} (P) in tetrahydrofuran (THF) solution and in solid poly(methylmethacrylate) (PMMA) matrix, by Z-scan technique is reported. The Z-scan traces reveal that the composite films exhibit large negative nonlinear refractive index of the order 10-10 esu. The excited-state absorption cross-section was found to be larger than the ground-state absorption indicating that the operating nonlinear process is reverse saturable absorption (RSA). The new polymer P exhibits good optical power limiting properties in the nanosecond regime in solution and as well in solid PMMA matrix. © 2009 Elsevier Ltd. All rights reserved.Item 3,3?-Benzene-1,4-diylbis[1-(substituted)phenylprop-2-en-1-one] derivatives: A new class of materials for third-order nonlinear optical applications(2010) Poornesh, P.; Ravi, K.; Umesh, G.; Hegde, P.K.; Manjunatha, M.G.; Manjunatha, K.B.; Vasudeva Adhikari, A.V.We have investigated the third-order nonlinear optical parameters of Bischalcones embedded in DMF solution and in solid PMMA matrix, by Z-scan technique using nanosecond laser pulse trains at 532 nm. Z-scan results reveal that the Bischalcones exhibits negative nonlinear refractive index as high as 10-11 esu. The molecular two-photon absorption cross-section ?2? of Bischalcones were of the order 10-46 cm4 s/photon, which is nearly two orders of magnitude larger than that of Rhodamine 6G which is 10-48 - 10-50 cm4 s/photon. We found that, the two-photon absorption (TPA) is the dominating nonlinear process leading to nonlinear absorption in both the cases in solution and as well as in solid medium. Based on TPA process, the Bischalcones exhibit good optical power limiting of nanosecond laser pulses at the input wavelength. The nonlinear optical parameters found to increase on enhancing the strength of the electron donor groups indicating the dependence and importance of electron donor/acceptor units on third-order nonlinear optical susceptibility ?(3). © 2009 Elsevier B.V. All rights reserved.Item Synthesis and characterization of a new NLO-active donor-acceptor-type conjugated polymer derived from 3,4-diphenylthiophene(2010) Manjunatha, M.G.; Vasudeva Adhikari, A.V.; Hegde, P.K.; Suchand Sandeep, C.S.; Philip, R.A new donor-acceptor-type conjugated polymer (P1) carrying 3,4-diphenylthiophene, 2,5-dihexyloxybenzene, and 1,3,4-oxadiazole units was synthesized through multistep reactions. The polymer was prepared using a polyhydrazide precursor route. The polymer has a well-defined structure and exhibits good thermal stability, with a decomposition onset temperature in nitrogen of 300 °C. Cyclic voltammetry experiments revealed that the polymer has low-lying LUMO (-3.68 eV) and high-lying HOMO (-5.78 eV) energy levels. The electrochemical band gap was found to be 2.10 eV. The UV-visible absorption spectrum of the polymer presented a maximum at 373 nm, and it displayed bluish-green fluorescence in dilute chloroform solution. The nonlinear optical properties of the new polymer were investigated at 532 nm using the Z-scan technique with nanosecond laser pulses. The polymer exhibited strong optical limiting behavior due to excited state absorption, which was phenomenologically similar to a three-photon absorption (3PA) process. The 3PA coefficient ? was found to be 7×10-22 m3/W2. The studies show that the new polymer (P1) is a promising material for developing efficient photonic devices.