| dc.description.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. |
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