Litty, Irimpan; Bindu, Krishnan; Nampoori, V P N; Radhakrishnan, P(Optical Society of America, August 20, 2008)
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Abstract:
We present the spectral and nonlinear optical properties of ZnO-SiO2 nanocomposites prepared by colloidal chemical synthesis. Obvious enhancement of ultraviolet (UV) emission of the samples is observed, and the strongest UV emission of a typical ZnO-SiO2 nanocomposite is over three times stronger than that of pure ZnO. The nonlinearity of the silica colloid is low, and its nonlinear response can be improved by making composites with ZnO. These nanocomposites show self-defocusing nonlinearity and good nonlinear absorption behavior. The observed nonlinear absorption is explained through two photon absorption followed by weak free carrier absorption and nonlinear scattering. The nonlinear refractive index and the nonlinear absorption increase with increasing ZnO volume fraction and can be attributed to the enhancement of exciton oscillator strength. ZnO-SiO2 is a potential nanocomposite material for the UV light emission and for the development of nonlinear optical devices with a relatively small limiting threshold.
Moosad, K P B; Abdul Rasheed, T M; Nampoori, V P N; Sathianandan, K(Optical Society of America, 1990)
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Abstract:
Low power optical phase conjugation in polyvinyl alcohol
films embedded with saturable dyes is reported. Phase
conjugate reflectivity achieved is higher than that obtained
in the case of similar gelatin films.
Nampoori, V P N; Litty, Irimpan; Bindu, Krishnan; Radhakrishnan, P(Elsevier Journal of Colloid and Interface Science, April 29, 2008)
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Abstract:
In this article we present the spectral and nonlinear optical properties of ZnO–TiO2 nanocomposites prepared
by colloidal chemical synthesis. Emission peaks of ZnO–TiO2 nanocomposites change from 340 nm
to 385 nm almost in proportion to changes in Eg. The nanocomposites show self-defocusing nonlinearity
and good nonlinear absorption behaviour. The nonlinear refractive index and the nonlinear absorption
increase with increasing TiO2 volume fraction at 532 nm and can be attributed to the enhancement of
exciton oscillator strength. ZnO–TiO2 is a potential nanocomposite material for the tunable light emission
and for the development of nonlinear optical devices with a relatively small limiting threshold
Swapna, Nair S; Rajesh, S; Abraham, V S; Anantharaman, M R; Nampoori, V P N(Elsevier, 2006)
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Abstract:
Fine magnetic particles (size≅100 Å) belonging to the series ZnxFe1−xFe2O4 were synthesized by cold co-precipitation methods and their structural properties were evaluated using X-ray diffraction. Magnetization studies have been carried out using vibrating sample magnetometry (VSM) showing near-zero loss loop characteristics. Ferrofluids were then prepared employing these fine magnetic powders using oleic acid as surfactant and kerosene as carrier liquid by modifying the usually reported synthesis technique in order to induce anisotropy and enhance the magneto-optical signals. Liquid thin films of these fluids were prepared and field-induced laser transmission through these films was studied. The transmitted light intensity decreases at the centre with applied magnetic field in a linear fashion when subjected to low magnetic fields and saturate at higher fields. This is in accordance with the saturation in cluster formation. The pattern exhibited by these films in the presence of different magnetic fields was observed with the help of a CCD camera and was recorded photographically.
Rajasree, K; Vidyalal, V; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(American Institute of Physics, August 1, 1993)
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Abstract:
Laser‐induced damage and ablation thresholds of bulk superconducting samples of Bi2(SrCa)xCu3Oy(x=2, 2.2, 2.6, 2.8, 3) and Bi1.6 (Pb)xSr2Ca2Cu3 Oy (x=0, 0.1, 0.2, 0.3, 0.4) for irradiation with a 1.06 μm beam from a Nd‐YAG laser have been determined as a function of x by the pulsed photothermal deflection technique. The threshold values of power density for ablation as well as damage are found to increase with increasing values of x in both systems while in the Pb‐doped system the threshold values decrease above a specific value of x, coinciding with the point at which the Tc also begins to fall.
Nampoori, V P N; Senoy, Thomas; Jinesh, Mathew; Radhakrishnan, P; George, A K; Al-Harthi,R V; Ramanujan, R V; Anantharaman, M R(Sensors and Actuators: A Physical, May 11, 2010)
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Abstract:
Metallic glass alloy Metglas 2826 MB based amorphous magnetic thin films were
fabricated by the thermal evaporation technique. Transmission electron micrographs and
electron diffraction pattern showed the amorphous nature of the films. Composition of
the films was analyzed employing x-ray photoelectron spectroscopy and energy
dispersive x-ray spectroscopy techniques. The film was integrated to a long period fibre
grating. It was observed that the resonance wavelength of the fibre grating decreased with
an increase in the magnetic field. Change in the resonance wavelength was minimal at
higher magnetic fields. Field dependent magnetostriction values revealed the potential
application of these films in magnetostrictive sensor devices
Sasi Kumar, P R; Nampoori, V P N; Vallabhan, C P G(Springer, May , 1994)
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Abstract:
The changes in emission characteristics of a neon hollow cathode discharge by resonant laser excitation of 1s 5→2p 2 and 1s 5→2p 4 transition have been studied by simultaneously monitoring the optogalvanic effect and the laser induced fluorescence. It has been observed that resonant excitation causes substantial variation in the relative intensities of lines in the emission spectrum of neon discharge.
Nampoori, V P N; Samuel, Varghese; Suresh, Nair; Girijavallabhan, C P(Elsevier, Journal of Optics Communications, November 26, 2008)
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Abstract:
A new method for the fabrication of high uniformity monolithic 1 x 4 single mode fused coupler is
described together with details of its performance in terms of coupling ratio, spectral response and uniformity.
The fabricated device exhibits ultra-broadband performance with a port-to-port uniformity of
0.4 dB. The reliability of such couplers is also evaluated and found to have good stability. Moreover, by
controlling the process parameters it is possible to control the power remaining in the through put port
of the device, which can be used for dedicated non-intrusive network health monitoring.
Aneeshkumar, B; Pramod, Gopinath; Jayan,Thomas; Vallabhan, C P G; Nampoori, V P N; Radhakrishnan, P(Elsevier, June , 2004)
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Abstract:
The nanosecond optical limiting characteristics of sandwich-type neodymium diphthalocyanine in a co-polymer matrix of polymethyl methacrylate (PMMA) and methyl-2-cyanoacrylate have been studied for the first time. The measurements were performed using 9 ns laser pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. The optical limiting performance of neodymium diphthalocyanine in co-polymer host was studied at different linear transmission. Laser damage threshold was also measured for the doped and undoped co-polymer samples. The optical limiting response is attributed to reverse saturable absorption which is due to excited-state absorption.
Kumar, G A; Gin, Jose; Vinoy, Thomas; Unnikrishnan, N V; Nampoori, V P N(Elsevier, 2003)
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Abstract:
Optical absorption studies of phthalocyanines (Pc-s) in borate glass matrix have been reported for the first time. Measurements have been done corresponding to photon energies between 1.1 and 6.2 eV for free base, manganese, iron, nickel, molybdenum, cobalt and copper phthalocyanines. Several new discrete transitions are observed in the UV–vis region of the spectra in addition to a strong continuum component of absorption in the IR region. Values of some of the important optical constants viz. absorption coefficient (α), molar extinction coefficient (ε), absorption cross-section (σa), band width (Δλ), electric dipole strength (q2) and oscillator strength (f) for the relevant electronic transitions are also presented. All the data reported for Pc-s in the new matrix have been compared with those corresponding to solution, vapor and thin film media.
Lalaja, Varghese; Nampoori, V P N; Pratap, R(Current Science, October 20, 1987)
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Abstract:
A mathematical analysis of an electroencephalogram of a human Brain during an epileptic
seizure shows that the K2 entropy decreases as compared to a clinically normal brain while the
dimension of the attractor does not show significant deviation.
Unnikrishnan, K P; Nampoori, V P N; Ramakrishnan, V; Umadevi, M; Vallabhan, C P G(Institute of Physics Publishing, 2003)
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Abstract:
Nonlinear optical absorption in silver nanosol was investigated at selected wavelengths (456 nm, 477 nm and 532 nm) using open aperture Z-scan technique. It was observed that nature of nonlinear absorption is sensitively dependent on input fluence as well as on excitation wavelength. Besides, the present sample was found to exhibit reverse saturable absorption (RSA) and saturable absorption (SA) at these wavelengths depending on excitation fluence. RSA is attributed to enhanced absorption resulting from photochemical changes. SA observed for fluence values lower and higher than those corresponding to RSA are, respectively, attributed to plasmon bleach and saturation of RSA.
Litty, Irimpan; Bindu, Krishnan; Nampoori, V P N; Radhakrishnan, P(Elsevier, 2008)
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Abstract:
In this article we present the nonlinear optical properties of ZnO–TiO2–SiO2 nanocomposites prepared by colloidal chemical synthesis. Nonlinear optical response of these samples is studied using nanosecond laser pulses at an off-resonance wavelength. The nonlinearity of the silica colloid is low and its nonlinear response can be improved by making composites with ZnO and TiO2. These nanocomposites show self-defocusing nonlinearity and good nonlinear absorption behaviour. The nonlinear refractive index and the nonlinear absorption increases with increasing ZnO volume fraction. The observed nonlinear absorption is explained by two photon absorption followed by weak free carrier absorption and nonlinear scattering. ZnO–TiO2–SiO2 is a potential nanocomposite material for the development of nonlinear optical devices with a relatively small limiting threshold.
Litty, Irimpan; Deepthy, A; Bindu, Krishnan; Nampoori, V P N; Radhakrishnan, P(Springer, 2008)
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Abstract:
In the present work, we have investigated the nonlinear
optical properties of self-assembled films formed from
ZnO colloidal spheres by z-scan technique. The sign of the nonlinear
component of refractive index of the material remains
the same; however, a switching from reverse saturable absorption
to saturable absorption has been observed as the material
changes from colloid to self-assembled film. These different
nonlinear characteristics can be mainly attributed to ZnO defect
states and electronic effects when the colloidal solution is
transformed into self-assembled monolayers. We investigated
the intensity, wavelength and size dependence of saturable and
reverse saturable absorption of ZnO self-assembled films and
colloids. Values of the imaginary part of third-order susceptibility
are calculated for particles of size in the range 20–300 nm
at different intensity levels ranging from 40 to 325MW/cm2
within the wavelength range of 450–650 nm.
Harilal, S S; Riju, C Issac; Bindhu, C V; Geetha K, Varier; Nampoori, V P N; Vallabhan, C P G(World Scientific Publishing Company, 1995)
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Abstract:
Pulsed photoacoustic measurements have been carried out in liquid CS2 using 532 nm radiation from a frequency doubled Nd:YAG laser. Variation of signal amplitude with laser fluence clearly indicates the role of multiphoton processes in the generation of photoacoustic effect. It is also shown that four photon induced dissociation and five photon induced ionization are likely processes in CS2 and 532 nm radiation.
Reethamma, Thomas; Nampoori, V P N(Elsevier, December , 1988)
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Abstract:
Photoluminescence, thermoluminescence and phosphorescence studies of cerium and copper doped BaS phosphors are attempted. Cu+ centres in BaS lattice activate red emission while Ce3+ sensitize the blue emission. Results are explained on the basis of superposition theory involving monomolecular kinetics. In Randall and Wilkins model, the decay and TL studies are found to corelate each other.
Nampoori, V P N; Girijavallabhan, C P; Harilal, S S; Riju, C Issac; Bindhu, C V(Journal of Physics D : Applied Physics, January 24, 1997)
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Abstract:
Optical emission studies of C2 molecules in plasma obtained by Nd:YAG
laser ablation of graphite in a helium atmosphere are reported for irradiances in the
range (1–9:2/ x 1010 W cm−2. The characteristics of the spectral emission intensity
from the C2 (Swan band) species have been investigated as functions of the
distance from the target, ambient pressure and laser irradiance. Estimates of
vibrational temperatures of C2 species under various irradiance conditions are
made. Results of measurements performed under different ambient helium gas
pressures are also discussed.
Aneeshkumar, B; Pramod, Gopinath; Vallabhan, C P G; Nampoori, V P N; Radhakrishnan, P(Optical Society of America, July , 2003)
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Abstract:
The nanosecond optical-limiting characteristics (at 532 nm) of some rare-earth metallo-phthalocyanines (Sm(Pc)2, Eu(Pc)2, and LaPc) doped in a copolymer matrix of poly(methyl methacrylate) and methyl-2-cyanoacrylate have been studied for the first time to our knowledge. The optical-limiting response is attributed to reverse saturable absorption due to excited-state absorption. The performance of LaPc in a copolymer host is studied at different linear transmissions. The laser damage thresholds of all the samples are also reported.
Kumar, G A; Vinoy, Thomas; Gin, Jose; Unnikrishnan, N V; Nampoori, V P N(Elsevier, 2002)
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Abstract:
Optical properties of free and substituted porphyrins (PP) doped borate glass matrix are reported for the first time. Absorption spectral measurements of H2TPP, CdTPP, MgTPP and ZnTPP doped borate glass matrix have been made in the 200–1100 nm region and the spectra obtained are analyzed to obtain the optical bandgap (Eg) and other important spectral parameters viz. oscillator strength (f), molar extinction coefficient (ε), electric dipole strength (q2), absorption cross-section (σa) and molecular concentration (N). Intense fluorescence was observed in the region 668–685 nm for CdTPP, ZnTPP and MgTPP doped matrices, whereas no such fluorescence was observed in H2TPP doped matrix. Fluorescence intensity was observed to be almost similar in all the metallated porphyrine matrices. Fluorescence bandwidth (Δλ), decay time (τ), stimulated emission cross-section (σ) and optical gain (G) of the principal fluorescence transitions corresponding to the Q-band excitation were also evaluated and discussed.
Abdul Rasheed, T M; Nampoori, V P N; Sathianandan, K(Chemical Physics, 1986)
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Abstract:
The vibrational overtone spectra 0f the liquid phase 1,2-dichloroethane and 1,2-dibromoethane in the spectral regions of
CH stretching local mode overtones corresponding to delta v CH= = 2 to delta v CH=5 are reported. The observed spectral features are
assigned using the local mode model. LocaI mode frequencies WCH and diagonal local mode anharmonicities XCH are
obtained from an analysis of the spectra. The local-local combinations observed are interpreted on the basis of a coupled CH
oscillator model hamiltonian. Local-normal combinations show complex structures and their possible assignments are given.