V P N Nampoori; Santhi Ani, Joseph; Misha, Hari; Mathew, S; Gaurav, Sharma; Soumya; Hadiya, V M; Radhakrishnan, P(Elsevier, Journal of Optics Communications, October 6, 2009)
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Abstract:
Dual beam mode-matched thermal lens method has been employed to measure the heat diffusion in
nanofluid of silver with various volumes of rhodamine 6G, both dispersed in water. The important observation
is an indication of temperature dependent diffusivity and that the overall heat diffusion is slower
in the chemically prepared Ag sol compared to that of water. The experimental results can be explained
assuming that Brownian motion is the main mechanism of heat transfer under the present experimental
conditions. Light induced aggregation of the nanoparticles can also result in an anomalous diffusion
behavior.
Santhi, A; Kala, U L; Nedumpara, R J; Kurian, A; Kurup, M R P; Radhakrishnan, P; Nampoori, V P N(Springer, 2004)
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Abstract:
The fluorescence spectrum of the schiff base obtained from salicylaldehyde and 2-aminophenol is studied using an argon-ion laser as the excitation source and its fluorescence quantum yield (Qf) is determined using a thermal lens method. This is a nondestructive technique that gives the absolute value of Qf without the need for a fluorescence standard. The quantum-yield values are calculated for various concentrations of the solution in chloroform and also for various excitation wavelengths. The value of Qf is relatively high, and is concentration dependent. The maximum value of Qf obtained is nearly 0.78. The high value of the fluorescence quantum yield will render the schiff base useful as a fluorescent marker for biological applications. Photostability and gain studies will assess its suitability as a laser dye.
Bindhu, C V; Harilal, S S; Achamma, Kurian; Nampoori, V P N; Vallabhan, C P G(World Scientific Publishing Company, 1998)
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Abstract:
Dual beam transient thermal lens studies were carried out in rhodamine 6G methanol solutions using 532 nm pulses from a frequency doubled Nd:YAG laser. Analysis of thermal lens signal shows the existence of different nonlinear processes like two photon absorption and three photon absorption phenomena along with one photon absorption. Concentration of the dye in the solution has been found to influence the occurrence of the different processes in a significant way.
V P N Nampoori; Radhakrishnan, P; Girijavallabhan, C P; Nibu, A George; George, A K(Applied Physics B Lasers and Optics, June 18, 2001)
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Abstract:
In this paper, we describe the use of an open cell
photoacoustic configuration for the evaluation of the thermal
effusivity of liquid crystals. The feasibility, precision and reliability
of the method are initially established by measuring
the thermal effusivities of water and glycerol, for which the
effusivity values are known accurately. In order to demonstrate
the use of the present method in the thermal characterization
of liquid crystals, we have measured the thermal
effusivity values in various mesophases of 4-cyano-4 -
octyloxybiphenyl (8OCB) and 4-cyano-4 -heptyloxybiphenyl
(7OCB) liquid crystals using a variable temperature open
photoacoustic cell. A comparison of the measured values for
the two liquid crystals shows that the thermal effusivities of
7OCB in the nematic and isotropic phases are slightly less
than those of 8OCB in the corresponding phases
Rajasree, K; Vidyalal, V; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(IOP, 1993)
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Abstract:
The phenomenon of mirage effect suffered by a He-Ne laser beam has been utilized to detect phase transitions in solids. It has been observed that anomalous fluctuations of large amplitude occur in the signal level near the transition temperature. The mean square value of the fluctuation is found to exhibit a well-defined peak at this point. Results of measurements made in the case of crystals of TGS ((NH2CH2COOH)3.H2SO4) and a ceramic sample (BaTiO3) are given to illustrate this technique.
Nampoori, V P N; Radhakrishnan, P; Girijavallabhan, C P; Nibu, A George; George, A K(Journal of Physics D : Applied Physics, October 13, 2000)
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Abstract:
We report on a laser induced photoacoustic study of the nematic-to-isotropic
transition in certain commercial nematic liquid crystal mixtures, namely BL001, BL002,
BL032 and BL035. A simple analysis of the experimental data using the
Rosencwaig–Gersho theory shows that the heat capacities of all these compounds exhibit a
sharp peak as the temperature of the sample is varied across the transition region. Also,
substantial differences in the photoacoustic signal amplitudes in nematic and isotropic phases
have been noticed for all the mixtures. The increased light scattering property of the nematic
phase may be the reason for the enhanced photoacoustic signal amplitude in this phase.
Nampoori, V P N; Litty, Irimpan; Radhakrishnan, P(Journal of Applied Physics, American Institute of Physics,, 2008)
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Abstract:
We describe the structure of luminescence spectrum in the visible region in nano-ZnO in colloidal
and thin film forms under weak confinement regime by modeling the transition from excited state
energy levels of excitons to their ground state. Measurements on nanocrystallites indicate the
presence of luminescence due to excitonic emissions when excited with 255 nm. The relevant
energy levels showing the transitions corresponding to the observed peaks in the emission spectrum
of ZnO of particle size 18 nm are identified.