Nampoori, V P N; Girijavallabhan, C P; Radhakrishnan, P; Thomas, K J; Sheeba, M(Journal of Optics A: Pure and Applied Optics, March 27, 2008)
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Abstract:
Polymethyl methacrylate (PMMA) optical fibres are fabricated by a preform drawing process.
The Raman spectra of PMMA fibres are recorded using a diode pumped solid state laser
emitting at 532 nm and a CCD-spectrograph in the 400–3800 cm−1 range. The variation of the
Raman intensity with the length of the optical fibre is studied. Investigations are carried out on
the variation of FWHM of the Raman peak at 2957 cm−1 with the length of the optical fibre and
pump power. The differential scattering cross section and gain coefficient of the Raman peak at
2957 cm−1 in PMMA are calculated in relation to that of toluene
Radhakrishnan, P; Girijavallabhan, C P; Nampoori, V P N; Thomas, K J; Sheeba, M(Journal of Optics A: Pure and Applied Optics, March 27, 2008)
[+]
[-]
Abstract:
Polymethyl methacrylate (PMMA) optical fibres are fabricated by a preform drawing process.
The Raman spectra of PMMA fibres are recorded using a diode pumped solid state laser
emitting at 532 nm and a CCD-spectrograph in the 400–3800 cm−1 range. The variation of the
Raman intensity with the length of the optical fibre is studied. Investigations are carried out on
the variation of FWHM of the Raman peak at 2957 cm−1 with the length of the optical fibre and
pump power. The differential scattering cross section and gain coefficient of the Raman peak at
2957 cm−1 in PMMA are calculated in relation to that of toluene.
Achamma, Kurian; Unnikrishnan, K P; Thomas Lee, S; Nampoori, V P N; Vallabhan, C P G(Taylor & Francis, 2002)
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Abstract:
A sensitive method based on the principle of photothermal phenomena to realize optical
logic gates is presented. A dual beam thermal lens method using low power cw lasers in a
dye-doped polymer can be very effectively used as an alternate technique to perform the
logical function such as NAND, AND and OR.
Nampoori, V P N; Kamalasanan, M N; Patel, M M(IOP, 1975)
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Abstract:
Indium monofluoride was excited in a high-frequency discharge and the C-X system was photographed at a reciprocal dispersion of 0.3 AA mm-1 using a plane-grating spectrograph. Rotational analyses of the 0,0 1,0 2,2 3,3 4,4 2,4 3,5 4,6 and 5,7 bands have been carried out and the following molecular constants have been evaluated. Be'=0.2670(+or-3) cm-1, Be"=0.2628(+or-4) cm-1, alpha e'=0.0050(+or-4) cm-1, alpha e"=0.0020(+or-1) cm-1, De'=3.65(+or-5)*10-7 cm-1, De"=2.5(+or-3)*10-7 cm-1, beta e'=0.5(+or-2)*10-7 cm-1, beta e"=0.2(+or-1)*10-7 cm-1, re'=1.9672(+or-3) AA, re"=1.9853(+or-2) AA. The re" value agrees with the microwave absorption value 1.9854 AA.
Kriashnan Nair, P R; Nandakumaran, V M; Ambika, G(Pramana, December , 1994)
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Abstract:
We establish numerically the validity of Huberman-Rudnick scaling relation for
Lyapunov exponents during the period doubling route to chaos in one dimensional maps. We
extend our studies to the context of a combination map. where the scaling index is found to
be different.
Bindu, Krishnan; Nampoori, V P N(Indian Academy of Sciences, June , 2005)
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Abstract:
Nanosized ZnO was prepared by polyol synthesis. Fluorescence spectrum of the ZnO colloid at varying pump intensities was studied. The powder was extracted and characterized by XRD and BET. The extracted powder was screen printed on glass substrates using ethyl cellulose as binder and turpinol as solvent. Coherent back scattering studies were performed on the screen printed sample which showed evidence of weak localization. The screen printed pattern showed strong UV emission.
Nithyaja, Balan; Misha, Hari; Nampoori, Vadakkedathu P N(Optical Society of America, July 1, 2009)
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Abstract:
A solid-state laser based on a dye-doped deoxyribonucleic acid (DNA) matrix is described. A thin solid film of DNA has been fabricated by treating with polyvinyl alcohol (PVA) and used as a host for the laser dye Rhodamine 6G. The edge emitted spectrum clearly indicated the existence of laser modes and amplified spontaneous emission. Lasing was obtained by pumping with a frequency-doubled Nd:YAG laser at 532 nm. For a pump energy of 10 mJ/pulse, an intense line with FWHM ≈0.2 nm was observed at 566 nm due to selective mode excitation.
Thomas Lee, S; Jose, Gin; Nampoori, V P N; Vallabhan, C P G; Unnikrishnan, N V; Radhakrishnan, P(IOP Publishing, 2001)
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Abstract:
The fabrication and characterization of a fibre optic pH sensor based on
evanescent wave absorption is presented. The unclad portion of a
multi-mode optical fibre is coated with a pH sensitive dye, which is
immobilized by the sol–gel route. The sensitivity of the device has been
found to increase when multiple sol–gel coatings are used as the sensing
region. The dynamic range and the temporal response of the sensor are
investigated for two different dyes, namely bromocresol purple and
bromocresol green. The performance of the device is evaluated in terms of
the results obtained during actual measurements.
Radhakrishnan, P; V P N Nampoori; Girijavallabhan, C P; Thomas Lee, S; Jose, Gin; Unnikrishnan, N V(Journal of Optics A: Pure and Applied Optics, July 12, 2001)
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Abstract:
The fabrication and characterization of a fibre optic pH sensor based on
evanescent wave absorption is presented. The unclad portion of a
multi-mode optical fibre is coated with a pH sensitive dye, which is
immobilized by the sol–gel route. The sensitivity of the device has been
found to increase when multiple sol–gel coatings are used as the sensing
region. The dynamic range and the temporal response of the sensor are
investigated for two different dyes, namely bromocresol purple and
bromocresol green. The performance of the device is evaluated in terms of
the results obtained during actual measurements
Girijavallabhan, C P; Radhakrishnan, P; Nampoori, V P N; Thomas Lee, S; Jose, Gin; Unnikrishnan, N V(Journal of Optics A : Pure and Applied Optics, July 12, 2001)
[+]
[-]
Abstract:
The fabrication and characterization of a fibre optic pH sensor based on
evanescent wave absorption is presented. The unclad portion of a
multi-mode optical fibre is coated with a pH sensitive dye, which is
immobilized by the sol–gel route. The sensitivity of the device has been
found to increase when multiple sol–gel coatings are used as the sensing
region. The dynamic range and the temporal response of the sensor are
investigated for two different dyes, namely bromocresol purple and
bromocresol green. The performance of the device is evaluated in terms of
the results obtained during actual measurements
V P N Nampoori; Radhakrishnan, P; Girijavallabhan, C P; Thomas Lee, S; Jose, Gin; Unnikrishnan, N V(Journal of Optics A: Pure and Applied Optics, July 12, 2001)
[+]
[-]
Abstract:
The fabrication and characterization of a fibre optic pH sensor based on
evanescent wave absorption is presented. The unclad portion of a
multi-mode optical fibre is coated with a pH sensitive dye, which is
immobilized by the sol–gel route. The sensitivity of the device has been
found to increase when multiple sol–gel coatings are used as the sensing
region. The dynamic range and the temporal response of the sensor are
investigated for two different dyes, namely bromocresol purple and
bromocresol green. The performance of the device is evaluated in terms of
the results obtained during actual measurements.
Sheeba, M; Rajesh, M; Mathew, S; Nampoori, V P N; Vallabhan, C P G; Radhakrishnan, P(Optical Society of America, April , 2008)
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Abstract:
Two-photon excited (TPE) side illumination fluorescence studies in a Rh6G-RhB dye mixture doped polymer optical fiber (POF) and the effect of energy transfer on the attenuation coefficient is reported. The dye doped POF is pumped sideways using 800 nm, 70 fs laser pulses from a Ti:sapphire laser, and the TPE fluorescence emission is collected from the end of the fiber for different propagation distances. The fluorescence intensity of RhB doped POF is enhanced in the presence of Rh6G as a result of energy transfer from Rh6G to RhB. Because of the reabsorption and reemission process in dye molecules, an effective energy transfer is observed from the shorter wavelength part of the fluorescence spectrum to the longer wavelength part as the propagation distance is increased in dye doped POF. An energy transfer coefficient is found to be higher at shorter propagation distances compared to longer distances. A TPE fluorescence signal is used to characterize the optical attenuation coefficient in dye doped POF. The attenuation coefficient decreases at longer propagation distances due to the reabsorption and reemission process taking place within the dye doped fiber as the propagation distance is increased.
Indic, P; Pratap, R; Nampoori, V P N; Pradhan, N(International Journal of Neuroscience, 1999)
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Abstract:
We propose to show in this paper, that the time series obtained from biological systems such as human brain are invariably nonstationary because of different time scales involved in the dynamical process. This makes the invariant parameters time dependent. We made a global analysis of the EEG data obtained from the eight locations on the skull space and studied simultaneously the dynamical characteristics from various parts of the brain. We have proved that the dynamical parameters are sensitive to the time scales and hence in the study of brain one must identify all relevant time scales involved in the process to get an insight in the working of brain.
Wilson,K J; Vallabhan, C P G(IOP Publishing, 1989)
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Abstract:
A simple and inexpensive linear magnetic field sweep generating system suitable for magnetic resonance experiments is described. The circuit, utilising a modified IC bootstrap configuration, generates field sweep over a wide range of sweep durations with excellent sweep linearity.
Santhi, A; Vinu V, Namboodiri; Radhakrishnan, P; Nampoori, V P N(American Institute of Physics, 2006)
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Abstract:
The authors apply the theory of photothermal lens formation and also that of pure optical nonlinearity to account for the phase modulation in a beam as it traverses a nonlinear medium. It is used to simultaneously determine the nonlinear optical refraction and the thermo-optic coefficient. They demonstrate this technique using some metal phthalocyanines dissolved in dimethyl sulfoxide, irradiated by a Q-switched Nd:YAG laser with 10 Hz repetition rate and a pulse width of 8 ns. The mechanism for reverse saturable absorption in these materials is also discussed.
Litty, Irimpan; Nampoori, V P N; Radhakrishnan, P; Bindu, Krishnan; Deepthy, A(American Institute of Physics, 2008)
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Abstract:
We have investigated the third-order nonlinearity in ZnO nanocolloids with particle sizes in the range 6-18 nm by the z-scan technique. The third-order optical susceptibility χ(3) increases with increasing particle size (R) within the range of our investigations. In the weak confinement regime, an R2 dependence of χ(3) is obtained for ZnO nanocolloids. The optical limiting response is also studied against particle size.
Litty, Irimpan; Nampoori, V P N; Radhakrishnan, P; Deepthy, A; Bindu, Krishnan(American Institute of Physics, 2007)
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Abstract:
In this article we present size dependent spectroscopic observations of nanocolloids of ZnO. ZnO is reported to show two emission bands, an ultraviolet (UV) emission band and another in the green region. Apart from the known band gap 380 nm and impurity 530 nm emissions, we have found some peculiar features in the fluorescence spectra that are consistent with the nanoparticle size distribution. Results show that additional emissions at 420 and 490 nm are developed with particle size. The origin of the visible band emission is discussed. The mechanism of the luminescence suggests that UV luminescence of ZnO colloid is related to the transition from conduction band edge to valence band, and visible luminescence is caused by the transition from deep donor level to valence band due to oxygen vacancies and by the transition from conduction band to deep acceptor level due to impurities and defect states. A correlation analysis between the particle size and spectroscopic observations is also discussed.
Sreekumar, J; Nandakumaran, V M(Physics Letters, October 21, 1985)
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Abstract:
The phenomenon of two-soliton resonances of the Kadomtsev-Petviashvilli equation for the superfluid surface density fluctuation in He films is studied. The velocity of the resonant soliton is obtained.
Sreekumar, J; Nandakumaran, V M(Springer, December , 1989)
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Abstract:
The dynamics of saturated two-dimensional superfluid4He films is shown to be governed by the Kadomtsev-Petviashvili equation with negative dispersion. It is established that the phenomena of soliton resonance could be observed in such films. Under the lowest order nonlinearity, such resonance would happen only if two dimensional effects are taken into account. The amplitude and velocity of the resonant soliton are obtained.
Bindhu, C V; Harilal, S S; Nampoori, V P N; Vallabhan, C P G(World Scientific, 1999)
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Abstract:
Dual beam thermal lens tecbnique is successfully employed for the determination of absolute
Fluorescence quantum yield of rhodamine 6G lnser dye in different solvents. A
532 nm radiation from a Q-switched Nd:YAG laser was used for the excitation purpose.
The fluorescence quantum yield values are found to be strongly influenced by environmental
effects. It has been observed that fluorescence yield is greater for rhodamine 6G
in ethylene glycol system than in water or in methanol. Our results also indicate that
parameters like concentration of the dye solution, aggregate formation and excited state
absorption affect the absolute values of fluorescence yield significantly.