Browsing by Author "Philip, R."

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A new donor-acceptor type conjugative poly{2-[4-(1-cyanoethenyl)phenyl]-3- (3,4-didodecyloxythiophen-2-yl)prop-2-enenitrile}: Synthesis and NLO studies
(2010) Hegde, P.K.; Vasudeva Adhikari, A.V.; Manjunatha, M.G.; Suchand Sandeep, C.S.; Philip, R.
This research article describes a technique to synthesize a new donor-acceptor type conjugated polymer carrying cyanophenylenevinylene and 3,4-didodecyloxy thiophene moieties, as an effective optical limiting material. It also includes the evaluation of its linear and nonlinear optical properties and electrochemical studies. The new polymer, viz., poly{2-[4-(1-cyanoethenyl) phenyl]-3-(3,4-didodecyloxythiophen-2-yl)prop-2-enenitrile} (P1) has been synthesized starting from 2,2?-sulfanediyldiacetic acid and diethyl ethanedioate through multistep reactions. In the final step, the polymerization was brought about by Knovenagel condensation. The newly synthesized intermediate, monomer and the polymer (P1) have been characterized by different spectroscopic techniques followed by elemental analysis. Its optical and electrochemical properties are investigated by UV-vis, fluorescence spectroscopy and cyclic voltammetric studies, respectively. The red colored polymer has a well defined structure, good thermal stability and a band gap of 1.78 eV. It emits green fluorescence both in solution and in film state. The third-order nonlinear optical property (NLO) of the polymer was studied by the Z-scan technique. The measurements were performed at 532 nm with 5 ns laser pulses using samples in solution form. An absorptive nonlinearity of the optical limiting type was found in this polymer, which is due to the combined action of saturable absorption and excited state absorption processes. These studies revealed that polymer P1 is a promising material for optical limiting applications. © 2010 Elsevier B.V.
A new nonlinear optically active donor-acceptor-type conjugated polymer: Synthesis and electrochemical and optical characterization
(2010) Manjunatha, M.G.; Vasudeva Adhikari, A.V.; Hegde, P.K.; Suchand Sandeep, C.S.S.; Philip, R.
A new donor-acceptor-type poly[3-{5-[3,4-didodecyloxy-5-(1,3,4-oxadiazol- 2-yl)thiophen-2-yl]-1,3,4-oxadiazol-2-yl}-9-dodecyl-9H-carbazole] (P) has been synthesized through multistep reactions. The new polymer P exhibited good thermal stability and film-forming behavior. The electrochemical band gap is estimated to be 2.15 eV. The polymer emits intense green fluorescence in the solid state. Third-order nonlinear optical (NLO) studies showed that the strong absorptive nonlinearity observed for the polymer is of the optical limiting type, which is due to an "effective" three-photon absorption (3PA) process. This 3PA process can have potential applications in photonic devices. The studies revealed that the new polymer P is a promising material for development of efficient optoelectronic devices. Â© 2010 TMS.
Design and synthesis of a new thiophene based donor-acceptor type conjugated polymer with large third order nonlinear optical activity
(2011) Vishnumurthy, K.A.; Vasudeva Adhikari, A.V.; Sunitha, M.S.; Ann Mary, K.A.A.; Philip, R.
In this communication we describe the design and synthesis of a new conjugated polymer (P) carrying 3,4-dialkoxythiophene, 1,3,4-oxadiazole and thienylene-vinylene units, from its monomers using Wittig condensation method. The structure of newly synthesized polymer was confirmed by FT-IR, 1H NMR, UV-vis spectral, elemental analysis and gel permeation chromatographic techniques. The polymer exhibited good thermal stability with the onset decomposition temperature around 320 °C in nitrogen atmosphere. Further, its electrochemical, linear and nonlinear optical properties have been investigated. The optical and electrochemical band gap was found to be 2.21 eV. Its third-order nonlinear optical property was investigated by Z-scan and DFWM techniques, using a Q-switched, frequency doubled Nd:YAG laser producing 7 ns laser pulses at 532 nm. Z-scan results reveal that the polymer exhibits self-defocusing nonlinearity. The operating mechanism involves reverse saturable absorption. The polymer shows strong optical limiting behavior due to effective two-photon absorption (2PA). The value of 2PA coefficient was found to be 3.0 × 10-11 mW, which is comparable to that of good optical limiting materials. The fluorescence quantum yield of the polymer in solution was determined using quinine sulfate as standard and it was found to be 35%. © 2011 Elsevier B.V. All rights reserved.
Effect of laser beam size on the dynamics of ultrashort laser-produced aluminum plasma in vacuum
(American Institute of Physics Inc. subs@aip.org, 2019) Sankar, P.; Shashikala, H.D.; Philip, R.
In laser-produced plasma experiments, the diameter of the irradiating laser beam on the target surface is a major parameter that influences the ablation mechanisms, plasma emission intensity, charged particle ejection, and plume morphology. In this work, the expansion dynamics of an ultrashort laser-produced aluminum plasma is investigated as a function of the laser beam size on the target, using a combination of diagnostic tools, viz., optical emission spectroscopy, fast gated time-resolved imaging, and ion current measurements. A Ti:sapphire laser delivering 100 fs, 6 mJ pulses at 800 nm is used for producing plasma from a pure Al target placed in vacuum (10 -5 Torr) at different positions with respect to the geometrical focus of the beam. Optical emission spectroscopic analysis of the plasma shows that higher emission intensities and ion populations are obtained for smaller beam sizes. Time-resolved Intensified Charge Coupled Device (ICCD) imaging of the expanding plasma shows a spherical morphology for plumes produced by smaller beam sizes and a cylindrical morphology for those produced by larger beam sizes. Temporal profiles of ion emission measured using a Faraday cup are in agreement with ICCD data, featuring a dual peak structure for larger beam sizes indicating distinct slow and fast ionic species, arising from changes in the ablation mechanism for varying laser fluences. Plume expansion is modelled by free expansion for the fast species and by shock wave propagation for the slow species. Ion flux and velocities are relatively high for smaller beam sizes. These studies can be of potential importance for laser processing applications, including laser welding, drilling, and micromachining. © 2019 Author(s).
Effect of Laser Beam Spot Size on the Dynamics of Ultrashort Laser-Produced Plasma in Vacuum
(Institute of Electrical and Electronics Engineers Inc., 2018) Sankar, P.; Shashikala, H.D.; HARILAL, S.S.; Philip, R.
The hydrodynamic expansion features of a laser-produced plasma is governed by initial plume conditions and hence the spot size of the laser beam.1-3 In this work, we investigated the expansion dynamics of a laser produced-plasma as a function of laser spot diameter in a vacuum environment (10-5 Torr) using multiple diagnostic tools. The diagnostic tools used were space-and time-resolved optical emission spectroscopy, 2-D fast-gated self-emission imaging and ion analysis using Faraday cup. The plume dynamics measured for varying spot sizes involves intriguing physics and hence demands detailed investigations, in view of a multitude of applications of laser ablation (LA) including elemental detection (LIBS, LA-LIF etc.), micromachining, laser-welding, nano-structuring, ion beam generation and pulsed laser deposition. Â© 2018 IEEE.
Electrochemical and nonlinear optical studies of new D-A type ?-conjugated polymers carrying 3,4-benzyloxythiophene, oxadiazole, and 3,4-alkoxythiophene systems
(2012) Sunitha, M.S.; Vasudeva Adhikari, A.V.; Vishnumurthy, K.A.; Smijesh, N.; Philip, R.
We investigated the nonlinear optical (NLO) properties of two newly synthesized conjugated polymers Pl and P2 carrying 1,3,4-oxadiazole, 3,4-dibenzyloxythiophene, and 3,4-dialkoxythiophene moieties along the main chain, as potential NLO active materials. Their structures have been well characterized. The nonlinear measurements were performed by Z-scan using 532 nm, 7 ns laser pulses. Calculated values of figure of merit and ? follow the criteria for good NLO materials. These results suggest that polymers are promising materials for applications in photonics.© 2012 The Chemical Society of Japan.
Enhanced bremsstrahlung X-ray emission from Ag nanoparticles irradiated by ultrashort laser pulses
(Elsevier B.V., 2019) Sankar, P.; Thomas, J.; Shashikala, H.D.; Philip, R.
In this work, an Ag nanoparticle colloidal suspension flowing in the form of a thin jet (250 ?m) is irradiated by 150 femtosecond, 800 nm laser pulses to form a plasma which emits bremsstrahlung X-rays of up to 100 keV energy. The flowing jet ensures long-term durability of the plasma source during continuous laser irradiation. The laser pulse is p-polarized and the angle of incidence is normal to the jet surface, to optimize resonance absorption of laser radiation by the plasma electron density gradient. A 30-fold enhancement is observed in the X-ray yield in the nanoparticle suspension, compared to the precursor salt solution. This is because of the local field enhancement (LFE) associated with the localized surface plasmon resonance (LSPR) in Ag nanoparticles. Multiphoton ionization will be greatly enhanced in the presence of LFE, resulting in the generation of a relatively larger number of free electrons, which become “hot” electrons of high kinetic energy by resonance absorption. Bremsstrahlung in the X-ray regime occurs due to the deceleration of these hot electrons. Under identical excitation conditions the corresponding X-ray enhancement measured in Au nanoparticles is relatively lower at 18-fold. This decrease is due to the higher ionization potential of Au (9.22 eV) as compared to Ag (7.58 eV). On the other hand, absorption spectra and SEM images measured after continuous irradiation reveal that Au nanoparticles are more photostable compared to Ag nanoparticles. These studies show that Ag nanoparticles are better suited for X-ray generation compared to Au nanoparticles under the experimental conditions employed. Applications include dynamics studies, microscopy, and lithography. © 2019
Ion dynamics of a laser produced aluminium plasma at different ambient pressures
(Springer Verlag service@springer.de, 2018) Sankar, P.; Shashikala, H.D.; Philip, R.
Plasma is generated by pulsed laser ablation of an Aluminium target using 1064 nm, 7 ns Nd:YAG laser pulses. The spatial and temporal evolution of the whole plasma plume, as well as that of the ionic (Al2+) component present in the plume, are investigated using spectrally resolved time-gated imaging. The influence of ambient gas pressure on the expansion dynamics of Al2+ is studied in particular. In vacuum (10?5 Torr, 10?2 Torr) the whole plume expands adiabatically and diffuses into the ambient. For higher pressures in the range of 1–10 Torr plume expansion is in accordance with the shock wave model, while at 760 Torr the expansion follows the drag model. On the other hand, the expansion dynamics of the Al2+ component, measured by introducing a band pass optical filter in the detection system, fits to the shock wave model for the entire pressure range of 10?2 Torr to 760 Torr. The expansion velocities of the whole plume and the Al2+ component have been measured in vacuum. These dynamics studies are of potential importance for applications such as laser-driven plasma accelerators, ion acceleration, pulsed laser deposition, micromachining, laser-assisted mass spectrometry, ion implantation, and light source generation. © 2017, Springer-Verlag GmbH Germany, part of Springer Nature.
Large third-order nonlinearity of new ?-conjugated donor-acceptor polymers with substituted thiophene and 1,3,4-oxadiazole moieties
(2012) Sunitha, M.S.; Vasudeva Adhikari, A.V.; Vishnumurthy, K.A.; Safakath, K.; Philip, R.
We present the synthesis of two newly designed, thiophene-based conjugated polymers (P1 and P2) carrying 1,3,4-oxadiazole, 3,4-dinaphthyloxy thiophene, and 3,4-dialkoxy thiophene moieties as potential NLO active materials. Their NLO properties have been investigated both by the Z-scan and degenerate four-wave mixing (DFWM) techniques using 532nm, 7 nanosecond laser pulses. The measured ? and ?(3) values for the polymers are found to be in the range of 1011m/W and 1011esu, respectively. The results indicate that they exhibit good optical-limiting behavior and are promising materials for nonlinear optical applications due to effective two-photon absorption (TPA). © 2012 Copyright Taylor and Francis Group, LLC.
New diphenylamine-based donor-acceptor-type conjugated polymers as potential photonic materials
(2011) Vishnumurthy, K.A.; Sunitha, M.S.; Philip, R.; Vasudeva Adhikari, A.V.
A new series of donor-acceptor-type conjugated polymers (P1 and P2) carrying a diphenyl amine moiety were synthesized via Wittig condensation technique. The polymers structures were well established by FT-IR, 1H NMR, elemental analysis and gel permeation chromatographic techniques. They exhibited good thermal stability with an onset decomposition temperature of approximately 325 °C under nitrogen atmosphere. The optical and electrochemical properties of the polymers were studied by UV-vis, fluorescence emission spectroscopy and cyclic voltammetry. They exhibited good fluorescence in dilute solutions and showed solvatochromic behavior in various polar solvents. The electrochemical studies revealed that the polymers possess low-lying LUMO energy levels that ranging from -3.47 to -3.73 eV and high-lying HOMO energy levels that ranging from -5.57 to -5.81 eV. The thirdorder nonlinear optical properties of the polymers were investigated using the Z-scan technique. The effective two-photon absorption (TPA) coefficients (?) of the polymers were found to be 0.645 × 10-10 and 0.212 × 10-10 m/W. © 2011 Elsevier Ltd. All rights reserved.
A new nonlinear optically active donor-acceptor-type conjugated polymer: Synthesis and electrochemical and optical characterization
(2010) Manjunatha, M.G.; Adhikari, A.V.; Hegde, P.K.; Suchand, Sandeep, C.S.; Philip, R.
A new donor-acceptor-type poly[3-{5-[3,4-didodecyloxy-5-(1,3,4-oxadiazol- 2-yl)thiophen-2-yl]-1,3,4-oxadiazol-2-yl}-9-dodecyl-9H-carbazole] (P) has been synthesized through multistep reactions. The new polymer P exhibited good thermal stability and film-forming behavior. The electrochemical band gap is estimated to be 2.15 eV. The polymer emits intense green fluorescence in the solid state. Third-order nonlinear optical (NLO) studies showed that the strong absorptive nonlinearity observed for the polymer is of the optical limiting type, which is due to an "effective" three-photon absorption (3PA) process. This 3PA process can have potential applications in photonic devices. The studies revealed that the new polymer P is a promising material for development of efficient optoelectronic devices. � 2010 TMS.
Nonlinear optical characterization of new thiophene-based conjugated polymers for photonic switching applications
(2011) Hegde, P.K.; Vasudeva Adhikari, A.V.; Manjunatha, M.G.; Suchand Sandeep, C.S.S.; Philip, R.
This research article describes a technique to synthesize new donor-acceptor-type conjugated polymers carrying 1,3,4-oxadiazolyl-naphthalene and 3,4-(ethylenedioxy/diphenyl)-thiophene moieties (P1 and P2) starting from 2,2?-sulfanediyldiacetic acid and diethyl ethanedioate through multistep reactions. The newly synthesized intermediates and the final polymers have been characterized by different spectroscopic techniques followed by elemental analysis. Their optical and electrochemical properties have been investigated by UV-visible, fluorescence spectroscopy, and cyclic voltammetric studies, respectively. Furthermore, the nonlinear optical transmission properties of these polymers have been investigated by the open aperture z-scan technique. The new polymers P1 and P2 have well-defined structures, good thermal stability, and band gaps of 1.98 and 1.88 eV, respectively. They emit bluish-green fluorescence both in solution and in film state. Interestingly, these polymers show saturable absorption behavior. The results of nonlinear optical studies reveal that they are potential candidates for photonic switching device applications. © 2011 Wiley Periodicals, Inc.
Nonlinear optical properties of a newly synthesized thiophene based conjugated polymer
(2011) Sunitha, M.S.; Adhikari, A.V.; Vishnumurthy, K.A.; Philip, R.
We have synthesized a new donor-acceptor (D-A) conjugated polymer containing 3,4-aralkyloxy and alkoxy substituted thiophene and 1,3,4-oxadiazole as donor and acceptor moieties respectively, through precursor polyhydrazide route. The required polyhydrazide was synthesized from 3,4-dihydroxythiophene diester through multistep reaction. The new polymer was characterized by using FTIR, 1H NMR spectroscopy, followed by Elemental analysis. The average molecular weight of the polymer was determined by Gel Permeation Chromatography. The band gap of the polymer was calculated by using UV-visible and cyclic voltametry. Further, its NLO properties in THF solution were investigated both by the Z-scan and degenerate four-wave mixing (DFWM) techniques using 532 nm, 7 nanosecond laser pulses. The results indicate that they exhibit good optical limiting behavior due to effective two-photon absorption (TPA). Values of the effective TPA coefficient (?), third-order non-linear optical susceptibility (?(3)) and figure of merit (F) were calculated. The optical and electrochemical properties reveal that the polymer is a promising candidate for opto-electronic applications. � 2011 American Institute of Physics.
Nonlinear optical properties of a newly synthesized thiophene based conjugated polymer
(2011) Sunitha, M.S.; Vasudeva Adhikari, A.V.; Vishnumurthy, K.A.; Philip, R.
We have synthesized a new donor-acceptor (D-A) conjugated polymer containing 3,4-aralkyloxy and alkoxy substituted thiophene and 1,3,4-oxadiazole as donor and acceptor moieties respectively, through precursor polyhydrazide route. The required polyhydrazide was synthesized from 3,4-dihydroxythiophene diester through multistep reaction. The new polymer was characterized by using FTIR, 1H NMR spectroscopy, followed by Elemental analysis. The average molecular weight of the polymer was determined by Gel Permeation Chromatography. The band gap of the polymer was calculated by using UV-visible and cyclic voltametry. Further, its NLO properties in THF solution were investigated both by the Z-scan and degenerate four-wave mixing (DFWM) techniques using 532 nm, 7 nanosecond laser pulses. The results indicate that they exhibit good optical limiting behavior due to effective two-photon absorption (TPA). Values of the effective TPA coefficient (Î²), third-order non-linear optical susceptibility (Ï‡(3)) and figure of merit (F) were calculated. The optical and electrochemical properties reveal that the polymer is a promising candidate for opto-electronic applications. Â© 2011 American Institute of Physics.
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.
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.
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.
Nonlinear optical studies on new conjugated poly{2,2 l-(3,4- dialkoxythiophene-2,5-diyl) bis[5-(2-thienyl)-1,3,4-oxadiazole]}s
(2010) Hegde, P.K.; Vasudeva Adhikari, A.V.; Manjunatha, M.G.; Suchand Sandeep, C.S.; Philip, R.
Three new donor-acceptor type poly{2,2 1-(3,4-dialkoxythiophene- 2,5-diyl)bis[5-(2-thienyl)-1,3,4-oxadiazole]}s (P1, P2, and P3) were synthesized starting from thiodiglycolic acid and diethyl oxalate through multistep reactions. The polymerization was carried out using chemical polymerization technique. The optical and charge-transporting properties of the polymers were investigated by UV-visible, fluorescence emission spectroscopic and cyclic voltammetric studies. The polymers showed bluish-green fluorescence in solutions. The electrochemical band gaps were determined to be 2.03, 2.09, and 2.17 eV for P1, P2, and P3, respectively. The nonlinear optical properties of new polymers were investigated at 532 nm using single beam Z-scan and degenerate four-wave mixing (DFWM) techniques with nanosecond laser pulses. The polymers exhibited strong optical limiting behavior due to "effective" three-photon absorption. Values of the effective three-photon absorption (3PA) coefficients, thirdorder nonlinear susceptibilities (? (3)), and figures (F) of merit were calculated. © 2010 Wiley Periodicals, Inc.
Nonlinear transmittance and optical power limiting in magnesium ferrite nanoparticles: effects of laser pulsewidth and particle size
(Royal Society of Chemistry, 2016) Perumbilavil, S.; Sridharan, K.; Abraham, A.R.; Janardhanan, H.P.; Kalarikkal, N.; Philip, R.
We report comparative measurements of size dependent nonlinear transmission and optical power limiting in nanocrystalline magnesium ferrite (MgFe2O4) particles excited by short (nanosecond) and ultrashort (femtosecond) laser pulses. A standard sol-gel technique is employed to synthesize particles in the size range of 10-50 nm, using polyvinyl alcohol as the chelating agent. The structure and morphology of the samples are studied using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Growth of the particles in time is tracked through Fourier transform infrared spectroscopy. Nonlinear transmission measurements have been carried out using the open aperture Z-scan technique employing 532 nm, 5 nanosecond pulses and 800 nm, 100 femtosecond pulses, respectively. The measured optical nonlinearity is primarily of a reverse saturable absorption (RSA) nature, arising mostly from excited state absorption for nanosecond excitation, and two-photon absorption for femtosecond excitation. The optical limiting efficiency is found to increase with particle size for both cases. The calculated nonlinear parameters indicate that these materials are potential candidates for optical limiting applications. © The Royal Society of Chemistry.
Novel N-substituted-5-phenyl-1H-pyrazole-4-ethyl carboxylates as potential NLO materials
(2013) Chandrakantha, B.; Isloor, A.M.; Sridharan, K.; Philip, R.; Shetty, P.; Padaki, M.
In the present investigation we have synthesized a novel series of N-substituted-5-phenyl-1H-pyrazole-4-ethyl carboxylates, which are characterized by 1H NMR, UV-Vis and FT-IR spectroscopy methods. The optical nonlinearity of the compounds in chloroform solution has been studied at 532nm using 5ns laser pulses, employing the open-aperture z-scan technique. It is found that compound 3c having carboxylic acid group and ester substituent has maximum nonlinearity. From measurements we conclude that compounds 3c (4-[4-(ethoxycarbonyl)-5-phenyl-1H-pyrazol-1-yl]benzoic acid) and 3e (ethyl 1-(2-bromophenyl)-5-phenyl-1H-pyrazole-4-carboxylate) are potential candidates for optical limiting applications. © 2011.