A laser induced photoacoustic technique has been employed to measure the thermal effusivity value of natural rubber latex
in the liquid as well as in the solid state. The nano Zinc Oxide particles synthesized via precipitation technique is incorporated to the
natural rubber latex. The influence of molar fractions of nanoparticles on the thermal effusivity value of host polymer is investigated.
Detailed analysis of the results shows that the rubber latex in the solid state exhibits lower value for the thermal effusivity value in
comparison to the liquid state. The molar fraction of the nanoparticle is found to influence the effective thermal effusivity value in a
substantial manner. Results are explained in terms of nanoparticle and phonon assisted thermal energy transport in these samples.
We report a study on the thermo optical properties of some nonlinear materials using the z scan technique. Both open aperture and closed aperture z scan transmittance signals were recorded to study the refractive and absorptive nonlinearities. The samples chosen were metal phthalocyanines viz CoPc, NiPc, ZnPc and CuPc. Dimethyl Formamide (DMF) and Dimethyl Sulphoxide (DMSO) were used as solvents. The laser source was the Q switched Nd: YAG with 10 Hz repetition rate and a pulse width of 7 ns. The Q switched envelope of the pulses give negative nonlinearity in all these samples which can be due to either thermal lens effect or electronic transitions among triplet states. Usually the thermal lens effect is neglected in z scan signals recorded using high repetition rate pulses. In our work, we have also carried out dual beam thermal lens measurements inside the sample, using a low power He-Ne as probe. We used the theory of the thermal lens formalism and also that of the Kerr type nonlinearities to interpret the obtained data. These studies yield the nonlinear optical constants and also the thermo optic constants of the samples under investigation.
We report a novel technique to enhance the thermal lens signal intensity by the use of silver nanosol. Thermal lens signal measurements of the laser dye rhodamine 6G dissolved in double distilled water has been carried out using the 532 nm excitation from a Diode pumped solid state (DPSS) laser, both in the presence and absence of silver sol for various concentrations. It has been observed that there is a very noticeable increase in signal intensity when silver nanosol is added to the dye solution. Though the enhancement varies with concentration, it is generally greater than 56 percent. The results presented in this work are of great importance to configuration and optimization of extremely sensitive thermal lens instruments, which is the trend in the development of analytical instruments. We have also carried out the fluorescence quantum yield (Qf) measurements of the dye using the dual beam thermal lens technique for two different pump powers and observed that at higher pump power there is only about 10% reduction in the quantum yield at low concentration in comparison with about 50% reduction at low pump power. At higher concentrations, the percentage reductions are almost identical in both cases.
In the present study, we report the design and development of a cost-effective, simple, sensitive LED - based fiber optic sensor for detecting trace amounts of chloride ions in water. A multimode plastic clad silica (PCS) fiber with the cladding removed and long period grating (LPG) written on its middle region acts as the sensing element. Exposure of the sensing region to water samples containing spectroscopic reagents for the detection of chloride ions causes evanescent wave absorption, which increases with increase in concentration. The limit of detection of the sensor is found to be a few parts per billion and the operational range covers more than five orders of magnitude.