Thomas,P T; George,K K(Department of Applied Economics, September , 1994)
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Abstract:
It is hoped that the present study by analysing the
dynamics of agrarian change and peasant mobility may contribute
to the on-going debate on this issue in India and other developing
countries. It may also help to throw light on the validity of some
of the theories formulated on the basis of experience in different
regions and at different times. The study is likely to be of
special importance as it covers an area which has one of the
highest densities of population. The area has also witnessed
sweeping changes in agrarian structure as a result of the most
radical land reforms among the Indian states.
V P N Nampoori; Radhakrishnan, P; Girijavallabhan, C P; Geetha, K; Rajesh, M(Journal of Optics A: Pure and Applied Optics, Institute of Physics Publishing, January 13, 2006)
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Abstract:
We present a compact solid-state laser based on leaky mode propagation
from a dye-doped polymer free-standing film waveguide. The edge emitted
spectrum clearly indicated the existence of periodic resonant modes. The
reflections from the lateral faces of the free-standing film provided the
optical feedback thus giving rise to a Fabry–Perot like optical cavity. This
together with the guidance through the gain medium gave rise to intense
narrow emission lines. For a pump energy of 1.82 mJ/pulse, an intense line
with FWHM ∼0.4 nmwas observed at 576.5 nm.
Radhakrishnan, P; V P N Nampoori; Girijavallabhan, C P; Geetha, K; Rajesh, M(Journal of Optics A: Pure and Applied Optics, Institute of Physics Publishing, January 13, 2006)
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[-]
Abstract:
We present a compact solid-state laser based on leaky mode propagation
from a dye-doped polymer free-standing film waveguide. The edge emitted
spectrum clearly indicated the existence of periodic resonant modes. The
reflections from the lateral faces of the free-standing film provided the
optical feedback thus giving rise to a Fabry–Perot like optical cavity. This
together with the guidance through the gain medium gave rise to intense
narrow emission lines. For a pump energy of 1.82 mJ/pulse, an intense line
with FWHM ∼0.4 nmwas observed at 576.5 nm.
Girijavallabhan, C P; Radhakrishnan, P; V P N Nampoori; Geetha, K; Rajesh, M(Journal of Optics A: Pure and Applied Optics, Institute of Physics Publishing, January 13, 2006)
[+]
[-]
Abstract:
We present a compact solid-state laser based on leaky mode propagation
from a dye-doped polymer free-standing film waveguide. The edge emitted
spectrum clearly indicated the existence of periodic resonant modes. The
reflections from the lateral faces of the free-standing film provided the
optical feedback thus giving rise to a Fabry–Perot like optical cavity. This
together with the guidance through the gain medium gave rise to intense
narrow emission lines. For a pump energy of 1.82 mJ/pulse, an intense line
with FWHM ∼0.4 nmwas observed at 576.5 nm.
Santhi Ani, Joseph; Gaurav, Sharma; Misha, Hari; Mathew, S; Radhakrishnan, P; Nampoori, V P N(Optical Society of America, 2010)
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Abstract:
We demonstrate the possibility of realizing, all-optical switching in gold nanosol. Two overlapping laser beams are used for this purpose, due to which a low-power beam passing collinear to a high-power beam will undergo cross phase modulation and thereby distort the spatial profile. This is taken to advantage for performing logic operations. We have also measured the threshold pump power to obtain a NOT gate and the minimum response time of the device. Contrary to the general notion that the response time of thermal effects used in this application is of the order of milliseconds, we prove that short pump pulses can result in fast switching. Different combinations of beam splitters and combiners will lead to the formation of other logic functions too.
Optical fiber based laser induced fluorescence (LIF)
measurements were carried out using Rhodamine B to analyze
two different species of bacteria , a Gram-positive bacteria
namely Bacillus smithii , and fibrin alginolvticus, a Gram-
negative bacteria . The fiber sensor was clearly able to distinguish
between the two species of bacteria . Quenching effect of the dye
Rhodamine B by Bacillus smithii was observed . The effect of dye
on the samples was also studied in detail.
V P N Nampoori(Wiley Inter Science, March 27, 2007)
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Abstract:
Optical fiber based laser induced fluorescence (LIF)
measurements were carried out using Rhodamine B to analyze
two different species of bacteria , a Gram-positive bacteria
namely Bacillus .cmithii , and fibrin alginolvticus, a Gram-'
negative bacteria . The fiber sensor was clearly able to distinguish
between the two species of bacteria . Quenching effect of the dye
Rhodamine B by Bacillus smitltii was observed . The effect of dye
on the samples was also studied in detail.
Reethamma, Thomas; Nampoori, V P N(Elsevier, 1990)
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Abstract:
Fluorescence of BaS: Sm phosphor has been studied using a pulsed Nitrogen laser (337.1 nm) as the excitation source. The spectrum consists of a broad band in the region 540–660nm superposed by the characteristic Sm3+ lines. Energy level splitting pattern of Sm3+ due to crystal field effects has been calculated and relevent field parameters are evaluated. Analysis shows that Sm3+ takes up Ba2+ substitutional sites.
Nibu A, George; Vallabhan, C P G; Nampoori, V P N; George, A K; Radhakrishnan, P(Taylor & Francis, 2001)
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Abstract:
In this paper we report the use of a laser induced phoroacoustic technique for the detection of multiple phase transitions in heptyl-oxy-cyanobiphenyl (70CB) and octyl-oxy-cyanobiphenyl (80CB) liquid crystals. The observed photoacoustic signal amplitude profile carries clear signatures of two tirst order transitions in 70CB and two tirst order and a second order transitions in 80CB. Analysis of the experimental data using Rosencwaig-Gersho theory shows that the sudden decrease in the photoacoustic (PA) signal amplitude during phase transitions is due to a sharp increase in the heat capacity of the samples near the transition temperatures.
Sajan, D George(Cochin University of Science & Technology, November , 2003)
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Abstract:
Discovery of coherent optical sources four decades ago has revolutionized all fields of scientific development. One of the path breaking applications of lasers is the emergence of various thermo optic techniques to unravel some of the mysteries of light matter interactions.Thermo optic technique is a valuable tool to evaluate optical and thermal properties of materials in solid,liquid and gaseous states .This technique can also be employed effectively in nondestructive quality evaluation. In this doctoral thesis , the use of photothermal techniques based on photoacoustic and photothermal deflection phenomena for the study of certain class of photonics materials such as semiconductors, nano metal dispersed ceramics, composites of conducting polymers and liquid crystals is elaborated.
Description:
International School of Photonics,
Cochin University of Science and Technology
Jacob, Philip; Manivannan, S; Dhanuskodi, S; Tiwari, S K(Springer, 2008)
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Abstract:
N-alkyl-2,6-dimethyl-4(1H)-pyridinones, salts of
4-dimethylaminopyridine and 2-amino-5-nitropyridine are considered
to be potential candidates for nonlinear optical (NLO)
applications, in particular for the generation of blue-green laser
radiation. Single crystals were grown following the slow evaporation
technique at constant temperature. Single-shot laserinduced
surface damage thresholds in the range 3–10 GW/cm2
were measured using a 18 ns Q-switched Nd:YAG laser. The
surface morphologies of the damaged crystals were examined
under an optical microscope and the nature of damage identified.
The Vicker’s microhardness was determined at a load of
98.07 mN. The thermal transport properties, thermal diffusivity
(α), thermal effusivity (e), thermal conductivity (K) and heat
capacity (Cp), of the grown crystals were measured by an improved
photopyroelectric technique at room temperature. All
the results are presented and discussed.
V P N Nampoori; Radhakrishnan, P; Girijavallabhan, C P; Sajan, D George; Aji, A Anapara; K G K Warrier(Proceedings of SPIE, 2003)
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Abstract:
In this paper, we report the measurements of thermal diffusivity of nano Ag metal dispersed ceramic alumina
matrix sintered at different temperatures using laser induced non-destructive photoacoustic technique. Measurements of
thermal diffusivity also have been carried out on specimens with various concentration of nano metal. Analysis of the
data is done on the basis of one-dimensional model of Rosencwaig and Gersho. The present measurements on the
thermal diffusivity of nano metal dispersed ceramic alumina shows that porosity has a great influence on the heat
transport and the thermal diffusivity value. The present analysis also shows that the inclusion of nano metal into
ceramic matrix increases its interconnectivity and hence the thermal diffusivity value. The present study on the samples
sintered at different temperature shows that the porosity of the ceramics varies considerably with the change in sintering
temperature. The results are interpreted in terms of phonon assisted heat transfer mechanism and the exclusion of pores
with the increase in sintering temperature
Radhakrishnan, P; V P N Nampoori; Girijavallabhan, C P; Sajan, D George; Aji, A Anapara; K G K Warrier(Proceedings of SPIE, 2003)
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Abstract:
In this paper, we report the measurements of thermal diffusivity of nano Ag metal dispersed ceramic alumina
matrix sintered at different temperatures using laser induced non-destructive photoacoustic technique. Measurements of
thermal diffusivity also have been carried out on specimens with various concentration of nano metal. Analysis of the
data is done on the basis of one-dimensional model of Rosencwaig and Gersho. The present measurements on the
thermal diffusivity of nano metal dispersed ceramic alumina shows that porosity has a great influence on the heat
transport and the thermal diffusivity value. The present analysis also shows that the inclusion of nano metal into
ceramic matrix increases its interconnectivity and hence the thermal diffusivity value. The present study on the samples
sintered at different temperature shows that the porosity of the ceramics varies considerably with the change in sintering
temperature. The results are interpreted in terms of phonon assisted heat transfer mechanism and the exclusion of pores
with the increase in sintering temperature
Girijavallabhan, C P; Radhakrishnan, P; V P N Nampoori; Sajan, D George; Aji, A Anapara; K G K Warrier(Proceedings of SPIE, 2003)
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Abstract:
In this paper, we report the measurements of thermal diffusivity of nano Ag metal dispersed ceramic alumina
matrix sintered at different temperatures using laser induced non-destructive photoacoustic technique. Measurements of
thermal diffusivity also have been carried out on specimens with various concentration of nano metal. Analysis of the
data is done on the basis of one-dimensional model of Rosencwaig and Gersho. The present measurements on the
thermal diffusivity of nano metal dispersed ceramic alumina shows that porosity has a great influence on the heat
transport and the thermal diffusivity value. The present analysis also shows that the inclusion of nano metal into
ceramic matrix increases its interconnectivity and hence the thermal diffusivity value. The present study on the samples
sintered at different temperature shows that the porosity of the ceramics varies considerably with the change in sintering
temperature. The results are interpreted in terms of phonon assisted heat transfer mechanism and the exclusion of pores
with the increase in sintering temperature.
Bindhu, C V; Harilal, S S; Riju C, Issac; Geetha K, Varier; Nampoori, V P N; Vallabhan, C P G(World Scientific Publishing Company, 1995)
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Abstract:
Measurement of thermal lensing signal as a function of laser power made in Rhodamine B solutions in methanol give clear evidence of two photon absorption process within certain concentration ranges when 488 nm Ar+ laser beam is used as the pump source. Only one photon process is found to occur when 514 nm and 476 nm beams are used as the pump.
The use of laser excitations at two wavelengths, 488 rim and 514 nm, produced by Argon ion laser in
two plants species, Vicia faba (faba bean) and Allium cepa L., is described to compare the mutagenicity and
the spectrum of chromosomal aberrations induced by laser at mitosis. The laser irradiation has been done
at two power levels 200 and 400 mW with power densities 2.25 mW cm 2 and 4.49 mW cm 2 and different
exposure times (10, 20, 30 and 40 min). The effect produced by laser is compared to those of UV rays and
y- radiations. Laser as in the case of other physical and chenucal mutagens causes a dose-dependent decrease
in mitotic chromosomal aberrations at these wavelengths. It is postulated that laser could be used as a new
radiation system for the induction of mutations.
A novel method of blending natural rubber with polyvinylchloride in the latex
stage was developed, Dioctyl phthalate (DOP) and Amine terminated natural rubber
(ATNR) were used as plasticisers, for improving the mechanical properties of
these blends. Properties of the latex stage blends were compared with those of
dry blends. Latex stage blends showed superior mechanical properties compared
to the blends prepared in the dry state. The ageing resistance, oil resistance and
processability were found to be improved by latex stage blending.