Browsing by Author "Umesh, G."
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Item ?(3) measurement and optical limiting studies of urea picrate(2011) Naseema, K.; Shyma, M.; Manjunatha, K.B.; Muralidharan, A.; Umesh, G.; Rao, V.The molecular charge complex urea picrate (UP) was synthesized and its third order nonlinear optical properties have been investigated using a single beam Z-scan technique with nanosecond laser pulses at 532 nm. Open aperture data of the compound indicates two photon absorption at this wavelength. The nonlinear refractive index n2, nonlinear absorption coefficient ?, magnitude of effective third order susceptibility ?(3), the second order hyperpolarizability ?h and the coupling factor ? have been estimated. The experimentally determined values of ?, n2, Re ?(3) and Im ?(3), ?h and ? of the compound UP are 2.146 cm/GW, -1.258×10-11 esu, -1.347×10-13 esu, 0.377×10-13 esu, 0.69×10-32 esu and 0.28, respectively. The compound exhibits good optical limiting at 532 nm with the limiting threshold of 80 ?J/pulse. Our studies suggest that compound UP is a potential candidate for optical device applications such as optical limiters. © 2011 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 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 A method to generate a single sub-50-as pulse by employing a 5-fs laser pulse with intensity above the saturation intensity, was proposed. The neon target medium of 0.5 mm length and 5 Torr pressure, was placed 10 mm beyond the laser focus. Harmonic radiation from neon atoms, was obtained by solving the time-dependent Schrödinger equation coupled with Maxwell equations. The results show that the positive chirp contained in the broad continuum radiation can be compensated by an x-ray filter with a negative group delay dispersion in the spectral region of interest.(American Physical Society, Single sub-50-attosecond pulse generation from chirp-compensated harmonic radiation using material dispersion) Kim, K.T.; Kim, C.M.; Baik, M.G.; Umesh, G.; Nam, C.H.2004Item Acetone planar laser-induced fluorescence for supersonic flow visualization in air and nitrogen jet(University of Malaya, 2014) Shelar, V.M.; Shrisha Rao, M.V.; Hegde, G.M.; Umesh, G.; Jagadeesh, G.; Reddy, P.J.Background: Laser based flow visualization techniques are indispensable tools for flow visualization in fluid dynamics and combustion diagnostics. Among these, PLIF is very popular because of its capability to give quantitative information about the flow. This paper reports the acetone tracer-based PLIF imaging of supersonic jet with air and nitrogen as bath gases. Methods: The tracer was seeded in the flow by purging bath gas through the liquid acetone at ambient temperature. Planar laser sheet from frequency quadrupled, Q-switched, Nd:YAG laser (266 nm) was used as an excitation source. Emitted PLIF images of a jet flow field were recorded on ICCD camera. Results: In this study, the dependence of PLIF images intensity on oxygen by comparing nitrogen jet with air in supersonic regime was presented. A lower temperature at the exit of the supersonic jet condenses the tracer which in turn forms droplets. Conclusions: There was a significant decrease in the PLIF image intensity in the case of air. This may be attributed to the oxygen present in the air. It is shown that image adding and Gaussian image processing of PLIF images for steadystate jet improve the quality of images. © 2014 Shelar et al.; licensee Springer.Item All optical nonlinear and switching characteristics of a novel ruthenium complex(Elsevier B.V., 2014) Manjunatha, K.B.; Dileep, R.; Umesh, G.; Satyanarayan, M.N.; Badekai Ramachandra, B.Third-order nonlinear optical properties of a novel ruthenium complex (2-thioxo-1,3-dithiole-4,5-dithiolato) triphenylarsenic Ru(III), have been investigated by employing Z-scan and DFWM techniques. The compound shows self-defocusing effect. Its nonlinear refractive index, third-order nonlinear optical susceptibility and the second-order hyperpolarizability are seen to be of the order of 10-9, 10-10 and 10-30 esu respectively. The nonlinear absorption coefficient is of the order of 10 -9 m/W. This material exhibits good optical power limiting capability which is seen to occur due to reverse saturable absorption. Experiments on all-optical switching action indicate that the sample can function as an optical inverter or a NOT gate. © 2014 Elsevier B.V. All rights reserved.Item All-optical switching and limiting properties of a Ru (II) Schiff-base complex for nonlinear optical applications(Institute of Physics Publishing michael.roberts@iop.org, 2017) Manjunatha, K.B.; Rajarao, R.; Umesh, G.; Badekai Ramachandra, B.R.; Poornesh, P.A salen-based ruthenium (Ru) (II) complex was synthesized for possible use in nonlinear optical device applications. The Ru complex was doped in a polymer matrix to fabricate films using a low-cost spin-coating technique. The third-order nonlinear optical parameters of the complex were investigated by Z-scan and degenerate four-wave mixing techniques. The study reveals two-order enhancement of third-order optical susceptibility ? (3) and exhibits superior limiting capability due to a reverse saturable absorption process. All-optical switching action for the films indicates that the sample can function as an optical inverter or a NOT gate. Hence, the Ru (II) Schiff-base complex materializes as a possible candidate for use in nonlinear optical devices. © 2017 Astro Ltd.Item Blue emitting 1,8-naphthalimides with electron transport properties for organic light emitting diode applications(Elsevier B.V., 2017) Ulla, H.; Raveendra Kiran, M.R.; Garudachari, B.; Ahipa, T.N.; Tarafder, K.; Vasudeva Adhikari, A.; Umesh, G.; Satyanarayan, M.N.In this article, the synthesis, characterization and use of two novel naphthalimides as electron-transporting emitter materials for organic light emitting diode (OLED) applications are reported. The molecules were obtained by substituting electron donating chloro-phenoxy group at the C-4 position. A detailed optical, thermal, electrochemical and related properties were systematically studied. Furthermore, theoretical calculations (DFT) were performed to get a better understanding of the electronic structures. The synthesized molecules were used as electron transporters and emitters in OLEDs with three different device configurations. The devices with the molecules showed blue emission with efficiencies of 1.89 cdA-1, 0.98 lmW?1, 0.71% at 100 cdm-2. The phosphorescent devices with naphthalimides as electron transport materials displayed better performance in comparison to the device without any electron transporting material and were analogous with the device using standard electron transporting material, Alq3. The results demonstrate that the naphthalimides could play a significant part in the progress of OLEDs. © 2017 Elsevier B.V.Item Blue emitting halogen-phenoxy substituted 1,8-naphthalimides for potential organic light emitting diode applications(Elsevier B.V., 2014) Ulla, H.; Raveendra Kiran, M.R.; Garudachari, B.; Satyanarayan, M.N.; Umesh, G.; Isloor, A.M.In this paper, we report the synthesis and characterization of six 1,8-naphthalimides [4a-4c and 5a-5c] obtained by the substitution of electron donating halogen-phenoxy groups at the C-4 position. The derivatives were characterized using 1H NMR, 13C NMR, mass spectra, FT-IR, single crystal XRD; photophysical, thermal, surface morphological and electrochemical properties were also investigated. The derivatives exhibit deep blue photoluminescence in the range 414-423 nm (in CHCl3) and 457-466 nm (in thin film state) on UV excitation with high Stokes' shifts and good chromaticity. The TGA and DSC analysis showed that the derivatives possess good thermal stability (271-284 °C) and melting points (138-201 °C). The HOMO and LUMO energy levels estimated by cyclic voltammetry are in the range 6.21-6.34 eV and 3.31-3.41 eV respectively corresponding to energy band gaps of 2.98-3.15 eV. These energy values are relatively higher than the commonly used electron transporting materials. The optical and electronic properties of the derivatives were tuned by the introduction of different electron donating halogen-phenoxy groups through C-4 position of the naphthalimide moiety. The emissive and electron-transporting properties of the naphthalimide derivative 4a were studied by fabricating a bi-layer and tri-layer devices. Further a phosphorescent device with 4a as electron transport layer (ETL) exhibited superior performance than the device without any ETL and was comparable with the device using standard Alq3 as ETL. These results indicate that the synthesized naphthalimide derivatives could play an important role in the development of OLEDs. © 2014 Elsevier B.V. All rights reserved.Item Blue light emitting materials for organic light emitting diodes: Experimental and simulation study(2012) Ulla, H.; Garudachari, B.; Satyanarayan, M.N.; Umesh, G.; Isloor, A.M.Novel blue light-emitting materials were designed by the substitution at the 4-position of 1,8-naphthalimide with electron-donating phenoxy group. The effect of molecular structure on the photophysical, electronic structure properties of the derivatives was explored by UV-visible absorption spectroscopy, photoluminescence spectroscopy, cyclic voltammetry and quantum chemical calculations. Both UV-visible absorption and emission spectra of derivatives indicate that the emission is in blue region. Electrochemical studies of the molecules revealed that they have low-lying energy levels of the lowest unoccupied molecular orbital (LUMO) and energy levels of the highest occupied molecular orbital (HOMO) indicating that the derivatives possess good electron-transporting or hole-blocking properties. To further reveal the electronic structure and the optical properties, the structural and electronic properties of the synthesized derivatives were calculated. These results indicate that molecules may offer potential as dopants as well as non-doping light-emitting materials with good electron injection capabilities for fabrication of blue organic light-emitting diodes. � 2012 IEEE.Item Blue light emitting materials for organic light emitting diodes: Experimental and simulation study(2012) Ulla, H.; Garudachari, B.; Satyanarayan, M.N.; Umesh, G.; Isloor, A.M.Novel blue light-emitting materials were designed by the substitution at the 4-position of 1,8-naphthalimide with electron-donating phenoxy group. The effect of molecular structure on the photophysical, electronic structure properties of the derivatives was explored by UV-visible absorption spectroscopy, photoluminescence spectroscopy, cyclic voltammetry and quantum chemical calculations. Both UV-visible absorption and emission spectra of derivatives indicate that the emission is in blue region. Electrochemical studies of the molecules revealed that they have low-lying energy levels of the lowest unoccupied molecular orbital (LUMO) and energy levels of the highest occupied molecular orbital (HOMO) indicating that the derivatives possess good electron-transporting or hole-blocking properties. To further reveal the electronic structure and the optical properties, the structural and electronic properties of the synthesized derivatives were calculated. These results indicate that molecules may offer potential as dopants as well as non-doping light-emitting materials with good electron injection capabilities for fabrication of blue organic light-emitting diodes. © 2012 IEEE.Item Blue light emitting naphthalimides for organic light emitting diodes(2013) Ulla, H.; Garudachar, B.; Satyanarayan, M.N.; Umesh, G.; Isloor, A.M.The photophysical, electrochemical, surface morphology and thermal properties of two novel blue lightemitting materials were studied. Results indicate that the molecules offer potential as non-doping light-emitting materials with good electron injection capabilities for fabrication of blue organic light-emitting diodes. � 2013 American Institute of Physics.Item Blue light emitting naphthalimides for organic light emitting diodes(2013) Ulla, H.; Garudachar, B.; Satyanarayan, M.N.; Umesh, G.; Isloor, A.M.The photophysical, electrochemical, surface morphology and thermal properties of two novel blue lightemitting materials were studied. Results indicate that the molecules offer potential as non-doping light-emitting materials with good electron injection capabilities for fabrication of blue organic light-emitting diodes. © 2013 American Institute of Physics.Item Blue organic light emitting materials: Synthesis and characterization of novel 1,8-naphthalimide derivatives(Elsevier B.V., 2014) Ulla, H.; Garudachari, B.; Satyanarayan, M.N.; Umesh, G.; Isloor, A.M.A series of naphthalimide derivatives were designed and synthesized by substituting electron-donating phenoxy groups at the 4th position of 1,8-naphthalimide. Photophysical, thermal, electrochemical properties of the synthesized derivatives were studied. The photophysical studies revealed that by varying the substituents at the 4th position of the 1,8-naphthalimide backbone, the photoluminescence spectra can be readily tuned in the range 410-423 nm (solution) and 457-468 nm (thin film). The derivatives have high Stokes' shifts and the Commission Internationale de l'Eclairage (CIE) coordinates are positioned in the deep blue region of the chromaticity diagram. Thermal analysis showed that the melting points are in the range 135-270 C with good thermal stability of 260-275 C. Electrochemical studies show the derivatives to have low-lying energy levels revealing that they possess good electron-transporting and hole-blocking properties. The ionization potentials and electron affinity are in the region of 6.30-6.36 eV and 3.31-3.43 eV, respectively, with energy band-gaps in the range 2.93-3.0 eV. The studies reveal that these energy values are relatively higher than the commonly used electron transporting materials. Hence these derivatives are potential candidates not only as electron transporting but also as hole blocking blue emitters for organic light-emitting diode applications. © 2013 Elsevier B.V. All rights reserved.Item Capacitance and impedance spectroscopy studies of polymer light emitting diodes based on MEH-PPV:BT blends(Elsevier Ltd, 2019) K M, N.K.; Sterin, N.S.; Das, P.P.; Umesh, G.; Satyanarayan, M.N.Light emitting polymer poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is blended with a wide bandgap electron transport material benzothiadiazole (BT) and its effect on the electronic properties has been studied by capacitance and impedance spectroscopy (IS) in PLEDs. The impedance data is fitted using equivalent circuit models and the minimum parallel resistance (Rp) at zero bias have been obtained for 1:3 ratio of MEH-PPV:BT blended devices. The negative capacitance (NC) shows the occurrence of the trap-assisted non-radiative recombination mechanism at low frequencies in the unblended MEH-PPV PLEDs. Further, this behavior is seen to be reduced in PLEDs with MEH-PPV:BT blends. This clearly suggests that the blending of MEH-PPV and BT at different weight ratios results in the suppression of trap-assisted recombination. This can be attributed to the elimination of trap states due to the dilution of semiconductor material on account of the addition of wide bandgap host material. Moreover, the blended devices have shown a significant improvement in the conductivity at small bias voltages. © 2019 Elsevier B.V.Item Charge Transport Investigations in Novel Triarylamine Derivatives Based Organic Devices(National Institute of Technology Karnataka, Surathkal, 2018) Fernandes, Jean Maria; Satyanarayan, M. N.; Umesh, G.Research on new organic semiconductor materials and their optoelectronic properties has been growing in prominence due to diverse potential applications. This thesis explores the charge transport properties of some novel triarylamine based organic semiconductors in hole-only devices to examine their suitability for OLED applications. Devices fabricated by physical vapor deposition are characterized using Impedance Spectroscopy as well as frequency and/or voltage dependent measurements of current density, capacitance and conductivity. The thickness dependent hole injection efficiency of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) film in devices of N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′- diamine (α-NPD) shows that the hole injection and transport properties reach a maximum for F4TCNQ film of optimum thickness of ~ 4 nm. The hole mobility of α-NPD (~ 10-5-10-4 cm2V-1s-1) is observed to increase over several orders of magnitude with its thickness and is found to be in good agreement with the literature. Following these studies, the electrical and optical properties of hole-only devices are investigated using triphenylamine (TPA) derivatives with either methyl or tert-butyl as side groups. This substitution is seen to improve charge transport properties. In addition to the above mentioned measurements, the role of side groups on the electrical and optical properties of the TPA derivatives is also investigated through UV-Vis and Photoluminescence (PL) spectroscopy. The frequency dependent analysis of charge carrier hopping rate reveals a crossover from dc to ac conductivity in the presence of a small ac bias. The new TPA molecules investigated are seen to possess hole mobility in the order of 10-7-10-6 cm2V-1s-1 and Photo Luminescence (PL) efficiency (~ 30%) which indicate their suitability for OLED applications.Item Coding In WDM Systems to Counter Impacts of SRS and Channel Beat Noise(International Academy of Microwave and Optical Technology (IAMOT), 2006) Mruthyunjaya, H.S.; Umesh, G.; Kumar, M.S.Depletion in power due to Stimulated Raman Scattering (SRS) impairs Wavelength Division Multiplexed (WDM) system performance. This is countered usually by placing optical amplifiers to maintain required Bit Error Rate (BER) performance. Also, impact of crosstalk in N x N WDM systems causes high noise power. In this paper we propose the use of block codes for forward error correction as a possible method for improving the performance of WDM systems in the presence of SRS and crosstalk. Our results show that with 200 users and with error control coding, the detector can effectively receive the required power and attain the desired BER performance in SRS limited WDM systems. Our results also show that the multiplexer crosstalk effectively comes down to -44 dB from -34 dB. © 2006 ISRAMT. All Rights Reserved.Item Concatenated Error Control Coding Applied to WDM Optical Communication Systems for Performance Enhancement(International Academy of Microwave and Optical Technology (IAMOT), 2007) Mruthyunjaya, H.S.; Umesh, G.; Kumar, M.Long haul incoherent optical multichannel communication systems employing N * N Wavelength Division Multiplexing (WDM) in presence of Stimulated Raman Scattering (SRS) and other receiver noises including channel and Amplified Spontaneous Emission (ASE) beat noises is analyzed. Concatenated error control coding techniques are employed to counter system degradation due to these limiting factors. It is shown that the Bit Error Rate (BER) of the order of 10-9 can be achieved for large values of N (=270) at link length of 200km without crossing SRS threshold of 1dB. Also power penalty due to multiplexer crosstalk effectively comes down from 5.5dB to 0.14dB for a 64 channel WDM system. © 2007 ISRAMT. All Rights Reserved.Item Design and analysis of a capacitively-coupled clamped-clamped MEMS resonator(2014) Umesh, G.; Nayak, B.M.G.; Deshpande, A.This document details the design, implementation and analysis of a clamped-clamped capacitively-coupled beam resonator with a high Q-factor [>10000] in the VHF band [30-300MHz]. The document also draws a parallel between simulation results and theoretical results of key performance metrics of the design. � 2014 IEEE.