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)
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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; 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
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
V P N Nampoori; Radhakrishnan, P; Girijavallabhan, C P; Nibu, A George; George, A K(Journal of Physics D : Applied Physics, October 13, 2000)
[+]
[-]
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.
Girijavallabhan,C P; V P N Nampoori; Radhakrishnan P; Thomas Lee S; Suresh Kumar P; Unnikrishnan K P; Sugunan S(INSTITUTE OF PHYSICS PUBLISHING, April 24, 2003)
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Abstract:
In this communication, we discuss the details of fabricating an off-line fibre
optic sensor (FOS) based on evanescent wave absorption for detecting trace
amounts of Fe3+ in water. Two types of FOS are developed; one type uses
the unclad portion of a multimode silica fibre as the sensing region whereas
the other employs the microbent portion of a multimode plastic fibre as the
sensing region. Sensing is performed by measuring the absorption of the
evanescent wave in a reagent medium surrounding the sensing region. To
evaluate the relative merits of the two types of FOS in Fe3+ sensing, a
comparative study of the sensors is made, which reveals the superiority of
the latter in many respects, such as smaller sensing length, use of a double
detection scheme (for detecting both core and cladding modes) and higher
sensitivity of cladding mode detection at an intermediate range of
concentration along with the added advantage that plastic fibres are
inexpensive. A detection limit of 1 ppb is observed in both types of fibre and
the range of detection can be as large as 1 ppb–50 ppm. All the
measurements are carried out using a LabVIEW set-up.
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)
[+]
[-]
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; 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.
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)
[+]
[-]
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; Sajan, D George; Aji, A Anapara; K G K Warrier(Proceedings of SPIE, 2003)
[+]
[-]
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; Ritty, J Nedumpara; Geetha, K; Dann, V J(Journal of Optics A: Pure and Applied Optics, Institute of Physics Publishing, January 9, 2007)
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Abstract:
We report unusual spectral narrowing and laser emission from polymer thin
films doped with Coumarin 540 dye. The laser emission from the polymer
films is found to be highly dependent upon the excitation length of the
medium. Even a short length of 1.75 mm of the dye doped film gave rise to
laser emission with FWHM of 0.3 nm for a pump intensity of 825 kW cm−2.
The partial reflections from the broad lateral surfaces of the free standing
films provided the optical feedback for the laser emission. Occurrence of
well-resolved equally spaced resonant modes confirmed the effect of a
Fabry–Perot-like optical cavity between the film surfaces