Bindhu, C V; Harilal, S S; Nampoori, V P N; Vallabhan, C P G(Indian Academy of Sciences, April , 1999)
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Abstract:
Thermal lensing effect was studied in aqueous solutions of rhodamine B using 532 nm,
9 ns pulses from a Nd:YAG laser. A low intensity He-Ne laser beam was used for probing the thermal
lens. Results obtained show that it is appropriate to use this technique for studying nonlinear absorption
processes like two photon absorption or excited state absorption and for analyzing dimerization
equilibria.
Harilal, S S; Bindhu, C V; Nampoori, V P N; Vallabhan, C P G(American Institute of Physics, 1999)
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Abstract:
Optical limiting and thermo-optic properties of C60 in toluene are studied using 532 nm, 9 ns pulses from a frequency-doubled Nd:YAG laser. Optical limiting studies in these fullerene molecules lead to the conclusion that reverse saturable absorption is the major mechanism for limiting properties in these molecules. Thermal lensing measurements are also performed in fullerene solutions. The quadratic dependence of thermal lens signal on incident energy confirms that enhanced optical absorption by the sample via excited triplet state absorption may play a leading role in the limiting property.
Thomas, Kuruvilla; Nandakumaran, V M(Elsevier, April , 1999)
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Abstract:
The effect of coupling on two high frequency modulated semiconductor lasers is numerically studied. The phase diagrams and bifurcatio.n diagrams are drawn. As the coupling constant is increased the system goes from chaotic to periodic behavior through a reverse period doubling sequence. The Lyapunov exponent is calculated to characterize chaotic and periodic regions.
Bindhu, C V; Harilal, S S; Nampoori, V P N; Vallabhan, C P G(Journal of Physics D: Applied Physics, 1999)
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Abstract:
Dual-beam transient thermal lens studies were carried out in aqueous solutions of
rhodamine 6G using 532 nm pulses from a frequency-doubled Nd:YAG laser. The analysis of
the observed data showed that the thermal lens method can effectively be utilized to study the
nonlinear absorption and aggregation which are taking place in a dye medium.
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.
Thomas, Kuruvilla; Nandakumaran, V M(American Institute of Physics, March , 1999)
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Abstract:
We have numerically studied the behavior of a two-mode Nd-YAG laser with an intracavity KTP crystal. It is found that when the parameter, which is a measure of the relative orientations of the KTP crystal with respect to the Nd-YAG crystal, is varied continuously, the output intensity fluctuations change from chaotic to stable behavior through a sequence of reverse period doubling bifurcations. The graph of the intensity in the X-polarized mode against that in the Y-polarized mode shows a complex pattern in the chaotic regime. The Lyapunov exponent is calculated for the chaotic and periodic regions.
Sankara Raman, S; Nampoori, V P N; Vallabhan, C P G; Ambadas, G; Sugunan, S(American Institute of Physics, February 1, 1999)
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Abstract:
The effect of the chemisorbed hydroxyl groups on the thermal diffusivity of gama alumina is determined
by evaluating the thermal diffusivity at various degassing temperatures and by doping it with rare
earth oxide using photoacoustic technique. The thermal diffusivity is found to decrease with the
increase in degassing temperature as well as with the increase in the doping concentration of rare
earth oxide. This decrease has been attributed to the loss of hydroxyl ion from the y-Al2O3.