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Author: search.filters.author.Umesh, G.Subject: search.filters.subject.Z-scan

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    Non linear optical properties of banana shaped liquid crystals
    (2011) Nagappa; Mahadeva, J.; Somashekar, R.; Yalemaggad, C.V.; Umesh, G.; Manjunatha, K.B.
    We report the nonlinear absorption and refraction of banana shaped liquid crystal, namely 1,3-phynelyne bis [N-(2-hydroxy-4-n-decyloxy-benzylidene)-4'- aminobenzoate] using Z-scan technique. The measurements were carried out using a Q-switched, frequency doubled Nd:YAG laser producing 7 nanosecond laser pulses at 532nm. The Z-scan result shows that the compound exhibits negative non-linearity. The nonlinear refractive index and nonlinear absorption coefficient of this compound were found to be -1.283 × 10-11 esu and 2.232cm/GW, respectively. The real and imaginary parts of the third-order nonlinear optical susceptibility were of the order of 10 -13 esu. The results suggest that these molecules are potential nonlinear optical materials for device applications. Copyright © Taylor & Francis Group, LLC.
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    Nonlinear optical studies of a novel pyrazoline
    (2012) Janardhana, K.; Ravindrachary, V.; Rajesh Kumar, P.C.R.; Umesh, G.; Manjunatha, K.B.; Ismayil, N.
    A novel pyrazoline, 3-(phenyl)-5-(4-hydroxyphenyl)-1-(2, 4-dinitrophenyl)-2-pyrazoline (PHDP) was synthesized using standard method and its chemical structure was confirmed using FTIR studies. The linear and non linear optical properties of the compound were studied using UV-Vis and Z-scan techniques. UV-Vis spectrum shows that the compound is transparent in the visible region and absorption in the UV region. The z-scan study shows that the compound possesses third and higher order optical nonlinearity. The calculated optical absorption cross sections indicate that the operating nonlinear mechanism is reverse saturable absorption type. The real part of the third-order nonlinear optical susceptibility χ3 was estimated and the closed aperture data shows that PHDP possess negative nonlinearity. © 2012 American Institute of Physics.
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    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.
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    ?(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.
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    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.
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    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.
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    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.
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    Nonlinear optical studies on 1,3-disubstituent chalcones doped polymer films
    (Elsevier, 2009) Poornesh, P.; Shettigar, S.; Umesh, G.; Manjunatha, K.B.; Prakash Kamath, K.; Sarojini, B.K.; Narayana, B.
    We report the measurements of the third-order nonlinear optical properties of recently synthesized and characterized two different 1,3-disubstituent chalcones doped PMMA films, with the prospective of reaching a good compromise between processability and high nonlinear optical properties. The measurements were done using nanosecond Z-scan at 532 nm. The Z-scan spectra reveal a large negative nonlinear refraction coefficient n2 of the order 10-11 esu and the molecular two photon absorption cross section is 10-46 cm4 s/photon. The doped films exhibit good optical power limiting property under nanosecond regime and the two photon absorption (TPA) is the dominating process leading to the nonlinear behavior. The improvement in the nonlinear properties has been observed when methylenedioxy group is replaced by dimethoxy group due to increase in conjugation length. The observed nonlinear parameters of chalcone derivatives doped PMMA film is comparable with stilbazolieum derivatives, a well-known class of optical materials for photonics and biophotonics applications, which suggests that, these moieties have potential for the application of all-optical limiting and switching devices. © 2008 Elsevier B.V. All rights reserved.
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    The third-order nonlinear optical properties of novel styryl dyes
    (2009) Shettigar, S.; Umesh, G.; Poornesh, P.; Manjunatha, K.B.; Asiri, A.M.
    The third-order nonlinear optical properties of two novel styryl dyes, namely, 1,3-diethyl-5-(4-methoxybenzylidene)-2-thioxodihydropyrimidine-4,6(1H,5H)-dione and 5-(3,4-dimethoxybenzylidene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione were studied using the Z-scan technique employing 7 ns laser pulses at 532 nm. The nonlinear refractive index, nonlinear absorption coefficient, magnitude of effective third-order susceptibility and coupling factor were determined. The optical power limiting behavior of the colorants was ascribed to two-photon absorption phenomenon. Nonlinear absorption cross-section increased with increase in ? electron density and the effective two-photon absorption cross-section was two orders of magnitude larger than those of commercially available azo compounds. The results suggest that these colorants offer promise as nonlinear optical materials for device applications. © 2009 Elsevier Ltd. All rights reserved.
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    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.