Faculty Publications
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Item Chalcones: Possible new materials for third-order nonlinear optics(Nova Science Publishers, Inc., 2011) Kiran, A.J.; Chandrasekharan, K.; Kalluraya, B.; Shashikala, H.D.'Search for potential materials' for third-order nonlinear optics has been of continuing interest in recent years. In this context, organic molecules are increasingly being recognized as the materials of the future because their molecular nature combined with the versatility of synthetic chemistry can be used to alter and optimize molecular structure to maximize third order nonlinear response. Chalcones have received considerable interest as materials for second-order nonlinear optical applications due to their ability to crystallize in noncentrosymmetric structure and their blue light transmittance. Being charge transfer compounds, chalcones can also possess large thirdorder nonlinearities due to their π-conjugated structure. In this article, we discuss the structure-nonlinear response relationship among a few chalcones and the possibility of using them for third-order applications. A meager or no work, to our knowledge, has been done so far on these molecules in this regard. Z-scan and degenerate four-wave mixing techniques were employed to investigate third-order optical nonlinearities of chalcone derivatives. Some of these molecules possess large χ (3) of magnitude as high as 10-12 esu and exhibit strong optical limiting properties. Possible mechanisms that are responsible for optical limiting property of these molecules have been discussed. . © 2011 by Nova Science Publishers, Inc. All rights reserved.Item Studies on nonlinear optical parameters of bis-chalcone derivatives doped polymer(Elsevier BV, 2006) Shettigar, S.; Chandrasekharan, K.; Umesh, G.; Sarojini, B.K.; Narayana, B.Two bis-chalcone derivatives, 1,5-[di(4-methoxyphenyl)]penta-1,4-dien-3-one and 1,5-[di(4-chlorophenyl)]penta-1,4-dien-3-one were synthesized. Their SHG conversion efficiencies are reported to be 6.0 and 5.0 times that of urea and hyper polarizabilities are 9.9×10-30 and 10.2×10-30 esu, respectively. The third-order nonlinear optical properties in PMMA matrix were studied by Z-scan technique using 7 ns laser pulses at 532 nm. The nonlinear refractive index ?, nonlinear absorption coefficient ?, magnitude of effective third order susceptibility ?(3) and the coupling factor ? have been investigated. The values obtained are of the order of 10-14 cm2/W, 1.2 cm/GW, 10-14 esu and 0.2, respectively, which are comparable with the values obtained in stilbazoleum like dyes. The experimental investigation also shows that they are very interesting optical limiting materials and their optical limiting behaviour is mainly due to two photon absorption phenomenon. © 2006 Elsevier Ltd. All rights reserved.Item ?(3) measurements and optical limiting in dibenzylideneacetone and its derivatives(2006) Kiran, A.J.; Chandrasekharan, K.; Nooji, S.R.; Shashikala, H.D.; Umesh, G.; Kalluraya, B.We investigated the third order nonlinear optical properties of dibenzylidene acetone (1,5-diphenyl-1, 4-pentadeine-3-one) and its derivatives. The nonlinear measurements were performed by using single beam Z-scan technique with Q-switched Nd:YAG nanosecond laser pulses at 532 nm. Open aperture data for dibenzylidene and its derivatives demonstrate the presence of two-photon absorption at this wavelength. The dependence of ?(3) on donor/acceptor type substituents to the basic compound clearly shows the electronic origin of nonlinearity and hence demonstrates that the mechanism by which the third order nonlinear response enhanced is not by the thermal effects, but instead due to the strong nonlinear absorption and nonlinear refraction of the compounds. The derivatives of the basic compound show very good optical limiting behavior. © 2005 Elsevier B.V. All rights reserved.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 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 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 Third order nonlinear optical properties and two photon absorption in newly synthesized phenyl sydnone doped polymer(2007) Shettigar, S.; Umesh, G.; Chandrasekharan, K.; Kalluraya, B.We have investigated third order nonlinear optical properties of three newly synthesized 3-phenyl sydnones, doped into PMMA and determined both real and imaginary part of ?(3). The measurements were performed using nanosecond laser pulses at 532 nm wavelength by employing Z-Scan technique. The nonlinear refractive index is found to be of the order of 10-14 cm2/W. The magnitude of third order susceptibility is of the order of 10-13 esu. Their two photon absorption coefficient and absorption cross section have also been determined. The optical power limiting behavior of sydnone moieties doped PMMA was also investigated. The results suggest that among the three organic phenyl sydnone moieties, 2-benzylhydrazono-5-(3-p-tolylsydnone-4-yl)1,3,4,-thiadiazine doped PMMA is a promising class of nonlinear optical material due to its simple molecular structure with p-tolyl group. It also shows a very good optical limiting behaviour with a limiting threshold of 0.21 mJ/pulse. The nonlinear parameters obtained are comparable with the values obtained in stilbazolium like dye such as trans-4-[2-(pyrrl)vinyl]-1-methylpyridium iodide. Hence this material may be tailored suitably for applications such as optical power limiters, switches and modulators. © 2007 Elsevier B.V. All rights reserved.Item Third order nonlinear optical properties and optical limiting in donor/acceptor substituted 4'-methoxy chalcone derivatives(2007) Ravindra, H.J.; John Kiran, A.; Chandrasekharan, K.; Shashikala, H.D.; Dharmaprakash, S.M.The third order nonlinear optical properties of 4'-methoxy chalcone and its derivatives have been investigated using a single-beam Z-scan technique with nanosecond laser pulses at 532 nm. The 4'-methoxy chalcone and its derivatives are donor-acceptor-acceptor (D-A-A) and donor-acceptor-donor (D-A-D) type intramolecular charge transfer molecules. The nonlinear response in these molecules was found to increase with increase in (a) the electron acceptor strength in D-A-A type and (b) the donor strength of the substituted group in D-A-D type molecules. The ?(3) value in these molecules is found to be of the order of 10-13 esu. The observed increase in the third order nonlinearity in these molecules clearly indicates the electronic origin. The compounds exhibit good optical limiting at 532 nm. The best optical limiting behavior was observed with the molecule substituted by a strong electron donor. © Springer-Verlag 2007.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.