Annieta, Philip K; Dr. Radhakrishnan, P(Cochin University of Science & Technology, October , 2004)
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Abstract:
The photoacoustic investigations carried out on different photonic
materials are presented in this thesis. Photonic materials selected for the
investigation are tape cast ceramics, muItilayer dielectric coatings, organic
dye doped PVA films and PMMA matrix doped with dye mixtures. The
studies are performed by the measurement of photoacoustic signal generated
as a result of modulated cw laser irradiation of samples. The gas-microphone
scheme is employed for the detection of photoacoustic signal. The different
measurements reported here reveal the adaptability and utility of the PA
technique for the characterization of photonic materials.Ceramics find applications in the field of microelectronics industry.
Tape cast ceramics are the building blocks of many electronic components
and certain ceramic tapes are used as thermal barriers. The thermal
parameters of these tapes will not be the same as that of thin films of the
same materials. Parameters are influenced by the presence of foreign bodies
in the matrix and the sample preparation technique. Measurements are done
on ceramic tapes of Zirconia, Zirconia-Alumina combination, barium
titanate, barium tin titanate, silicon carbide, lead zirconate titanateil'Z'T) and
lead magnesium niobate titanate(PMNPT). Various configurations viz. heat
reflection geometry and heat transmission geometry of the photoacoustic
technique have been used for the evaluation of different thermal parameters
of the sample. Heat reflection geometry of the PA cell has been used for the
evaluation of thermal effusivity and heat transmission geometry has been
made use of in the evaluation of thermal diffusivity. From the thermal
diffusivity and thermal effusivity values, thermal conductivity is also
calculated. The calculated values are nearly the same as the values reported for pure materials. This shows the feasibility of photoacoustic technique for
the thermal characterization of ceramic tapes.Organic dyes find applications as holographic recording medium and
as active media for laser operations. Knowledge of the photochemical
stability of the material is essential if it has to be used tor any of these
applications. Mixing one dye with another can change the properties of the
resulting system. Through careful mixing of the dyes in appropriate
proportions and incorporating them in polymer matrices, media of required
stability can be prepared. Investigations are carried out on Rhodamine 6GRhodamine
B mixture doped PMMA samples. Addition of RhB in small
amounts is found to stabilize Rh6G against photodegradation and addition of
Rh6G into RhB increases the photosensitivity of the latter. The PA technique
has been successfully employed for the monitoring of dye mixture doped
PMMA sample. The same technique has been used for the monitoring of
photodegradation ofa laser dye, cresyl violet doped polyvinyl alcohol also.Another important application of photoacoustic technique is in nondestructive
evaluation of layered samples. Depth profiling capability of PA
technique has been used for the non-destructive testing of multilayer
dielectric films, which are highly reflecting in the wavelength range selected
for investigations. Eventhough calculation of thickness of the film is not
possible, number of layers present in the system can be found out using PA
technique. The phase plot has clear step like discontinuities, the number of
which coincides with the number of layers present in the multilayer stack.
This shows the sensitivity of PA signal phase to boundaries in a layered
structure. This aspect of PA signal can be utilized in non-destructive depth profiling of reflecting samples and for the identification of defects in layered
structures.
Description:
International School of Photonics,
Cochin University of Science & Technology
Artificial neural networks (ANNs) are relatively new computational tools that have found extensive utilization in solving many complex real-world problems. This paper describes how an ANN can be used to identify the spectral lines of elements. The spectral lines of Cadmium (Cd), Calcium (Ca), Iron (Fe), Lithium (Li), Mercury (Hg), Potassium (K) and Strontium (Sr) in the visible range are chosen for the investigation. One of the unique features of this technique is that it uses the whole spectrum in the visible range instead of individual spectral lines. The spectrum of a sample taken with a spectrometer contains both original peaks and spurious peaks. It is a tedious task to identify these peaks to determine the elements present in the sample. ANNs capability of retrieving original data from noisy spectrum is also explored in this paper. The importance of the need of sufficient data for training ANNs to get accurate results is also emphasized. Two networks are examined: one trained in all spectral lines and other with the persistent lines only. The network trained in all spectral lines is found to be superior in analyzing the spectrum even in a noisy environment.
Abdul Rasheed, T M; Dr.Narayanan Nampoori, V P(Cochin University of Science and Technology, September 16, 1987)
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Abstract:
Vibrational overtone spectroscopy of X-H (X=C,N,O) containing molecules is an area of recent interest. The spectroscopic studies of higher vibrational levels yield valuable informations, regarding,the molecular structure, intra- and inter-molecular interactions, radiationless transitions, intra-molecular vibrational relaxations, multiphoton excitations and chemical reactivities, which cannot be z obtained by other spectroscopic methods. This thesis presents the results of experimental investigations on the overtone spectra of some organic compounds in the liquid phase for the characterization of CH bonds. The spectra in the fifth overtone region (1fiV=6) are recorded using a dual beam thermal lens setup and the lower overtones (.AV=2-5) are recorded spectrophotometrically.The thesis is presented in six chapters.
Description:
Department of Physics,Cochin University of Science and Technology
Harilal, S S; Girijavallabhan, C P(Cochin University of Science and Technology, 1997)
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Abstract:
This thesis is entitled “OPTICAL EMISSION DIAGNOSTICS OF LASER PRODUCED PLASMA FROM GRAPHITE AND YBa2Cu3O7. The work presented in this thesis covers the experimental results on the plasma produced with moderately high power laser with irradiance range in between 10 GW cm 2 to 100 GW cm -2. The characterization of laser produced plasma from solid targets viz. graphite and high temperature superconducting material like YBa2Cu3O7 have been carried out. The fundamental frequency from a Q - switched Nd: YAG laser with 9 ns pulse
duration is used for the present studies. Various optical emission emission diagnostic techniques were employed for the the characterization of the LPP which include emission spectroscopy, time resolved studies, line broadening method etc. In order to understand the physical nature of the LPP like recombination, collisional excitation and the laser interaction with plasma, the time resolved studies offer the most logical approach