Kailasnath, M; John, P R; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(Elsevier, 2008)
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Abstract:
This study was conducted to identify the concentration dependence of the operating wavelengths and the relative intensities in which a dye
mixture doped polymer optical fibre can operate. A comparative study of the radiative and Forster type energy transfer processes in Coumarin
540:Rhodamine 6G, Coumarin 540:Rhodamine B and Rhodamine 6G:Rhodamine B in methyl methacrylate (MMA) and poly(methyl methacrylate)
(PMMA) was done by fabricating a series of dye mixture doped polymer rods which have two emission peaks with varying relative intensities.
These rods can be used as preforms for the fabrication of polymer optical fibre amplifiers operating in the multi-wavelength regime. The 445 nm
line from an Nd:YAG pumped optical parametric oscillator (OPO) was used as the excitation source for the first two dye pairs and a frequency
doubled Nd:YAG laser emitting at 532 nm was used to excite the Rh 6G:Rh B pair. The fluorescence lifetimes of the donor molecule in pure
form as well as in the mixtures were experimentally measured in both monomer and polymer matrices by time-correlated single photon counting
technique. The energy transfer rate constants and transfer efficiencies were calculated and their dependence on the acceptor concentration was
analysed. It was found that radiative energy transfer mechanisms are more efficient in all the three dye pairs in liquid and solid matrices.
Kailasnath, M; Nishant, Kumar; Nampoori, V P N; Vallabhan, C P G; Radhakrishnan, P(Elsevier, 2008)
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Abstract:
Dependence of energy transfer parameters on excitation wavelength has been investigated in poly (methyl methacrylate) (PMMA) optical fibre preforms doped with C 540:Rh B dye mixture by studying the fluorescence intensity and the lifetime variations. A fluorescence spectrophotometer was used to record the excitation spectra of the samples for the emission wavelengths 495 and 580 nm. The fluorescence emission from the polymer rods was studied at four specific excitation wavelengths viz; 445, 465, 488 and 532 nm. The fluorescence lifetime of the donor molecule was experimentally measured in polymer matrix by time correlated single photon counting technique. The energy transfer rate constants and transfer efficiencies were calculated and their dependence on the acceptor concentration was analysed for three excitation wavelengths. It was found that any change in the excitation wavelength leads to significant variations in the quenching characteristics, which in turn affect the calculated energy transfer parameters.
Sebastian, P J; Dr.Sathianandan, K(Cochin University Of Science And Technology, November 25, 1981)
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Abstract:
Eventhough a large number of schemes have been proposed and develoned for N9 laser ouined dye lasers the
relatively low efficiency compelled the scientists to
device new methods to improve the system efficiencs.
Energy transfer mechanism has been shown to he a convenien
tool for the enhancement of efficiency of dye lasers. Th
p resent work covers a detailed study of the performance
characteristics of a N2 laser pumped dye laser in the con—
ventional mode and also, when pumped by the energy transfer
mechanism. For .th.e present investigations a dye laser
pumped by a'N2 laser (A4200 kw peak power) was fabricated.
The grating at grazing incidence was used as the beam expanding
device; A t its best performance the system was
giving an output peak power of l5 kW for a 5 X lC"3H/l Rh—€
solution in methanol. T he conversion efficiency was 7.5;
The output beam was having 3 divergence of 2 mrad and bandwidth
o.9 A. Suitable modifications were suggested for
obtaining better conversion efficiency and bandwidth.
Description:
Department of Physics,
Cochin University Of Science And Technology
Achamma, Kurian; Sajan, D George; Nampoori, V P N; Vallabhan, C P G(Elsevier, 2005)
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Abstract:
A sensitive method based on the principle of photothermal phenomena to study the energy transfer processes in organic dye mixtures is presented. A dual beam thermal lens method can be very effectively used as an alternate technique to determine the molecular distance between donor and acceptor in fluorescein–rhodamine B mixture using optical parametric oscillator.
Achamma, Kurian; Sajan, D George; Bindhu, C V; Nampoori, V P N; Vallabhan, C P G(Elsevier, 2007)
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Abstract:
The effect of pH on the fluorescence efficiency of fluorescein is evaluated using thermal lens technique. Fluorescence efficiency increases as the
sample becomes more and more alkaline. But when fluorescein is mixed with rhodamine B fluorescence quenching of fluorescein takes place with
the excitation of rhodamine B. The electronic energy transfer in this mixture is investigated using Optical Parametric Oscillator as the excitation
source. The effect of pH on the efficiency of energy transfer in fluorescein–rhodamine B mixture is presented.