Achamma Kurian

Studies on Fluorescence Efficiency and Photodegradation of Rhodamine 6G Doped PMMA Using a Dual Beam Thermal Lens Technique

In this paper we report the use of the dual beam thermal lens technique as a quantitative method to determine absolute fluorescence quantum efficiency and concentration quenching of fluorescence emission from rhodamine 6G doped Poly(methyl methacrylate) (PMMA), prepared with different concentrations of the dye. A comparison of the present data with that reported in the literature indicates that the observed variation of fluorescence quantum yield with respect to the dye concentration follows a similar profile as in the earlier reported observations on rhodamine 6G in solution. The photodegradation of the dye molecules under cw laser excitation is also studied using the present method.

Thermal lens spectrum of organic dyes using optical parametric oscillator

The wavelength dependence of thermal lens signal from organic dyes are studied using dual beam thermal lens technique. It is found that the profile of thermal lens spectrum widely differ from the conventional absorption spectrum in the case of rhodamine B unlike in the case of crystal violet. This is explained on the basis of varying contribution of nonradiative relaxations from the excited vibronic levels.

NONLINEAR ABSORPTION AND OPTICAL LIMITING IN SOLUTIONS OF SOME RARE EARTH SUBSTITUTED PHTHALOCYANINES

Effective nonlinear absorption coefficient, βeff, of solutions of some rare earth substituted phthalocyanines (viz: Sm(Pc)2, Eu(Pc)2 and LaPc) was measured using open aperture Z-scan technique under nanosecond pulse excitation at 532 nm. The effect of nonlinear absorption on optical limiting in these samples was also investigated. Both nonlinear absorption and optical limiting phenomena in these samples are attributed to sequential two-photon absorption (STPA) process.

STUDY OF ENERGY TRANSFER IN ORGANIC DYE PAIRS USING THERMAL LENS TECHNIQUE

It is demonstrated that the dual beam thermal lens technique can be very effectively used for the study of energy transfer processes in organic dye mixtures. The energy transfer rate and critical transfer radius in Rhodamine 6G — Rhodamine B are calculated using this technique. The observed results support Forster type resonance transfer due to long-range dipole–dipole interaction as reported by earlier workers using other techniques.

Thermo-optic characterization of neodymium/nickel doped silica glasses prepared via sol-gel route.

Intrinsic as well as rare earth (Neodymium) doped silica glasses with various molar ratio of dopant and a metallic (Nickel) co-dopant is prepared via sol-gel route. The structural characterization of the sample is carried out using X-ray diffraction and Fourier Transform Infrared Spectroscopy. The influence of dopant and doping concentration on the optical properties of silica matrix is investigated via UV-VIS absorption spectroscopy. Effect of dopant on thermal effusivity value of the host matrix is carried out by laser induced open cell photoacoustic technique. Analysis of the results showed that doping affect the thermal effusivity value and results are interpreted in terms of structural modification of the lattice and phonon assisted heat transport mechanism.

Realization of Optical Logic Gates Using the Thermal Lens Effect

A sensitive method based on the principle of photothermal phenomena to realize optical logic gates is presented. A dual beam thermal lens method using low power cw lasers in a dye-doped polymer can be very effectively used as an alternate technique to perform the logical function such as NAND, AND and OR.

Shape dependent heat transport through green synthesized gold nanofluids

Nanofluids hold promise as a more efficient coolant for thermoelectric devices. Despite the capability of tailoring the thermo physical properties of nanofluids, by tuning the particle parameters such as shape, size and concentration, the toxicity of chemicals used for the preparation of nanoparticles is a serious concern. Green synthesis of nanoparticles is emerging as an alternative to the conventional chemical and physical methods for the preparation of nanoparticles. In this work, the results of the preparation of gold nanoparticles using plant extracts as reducing agents are presented. The green synthesis route employed for the present study provides particles of similar size, but the shape of the particles is found to vary depending upon the source of the natural reducing agents. The thermal diffusivity values of the gold nanofluid measured using laser based dual beam thermal lens technique elucidate the role of shape and concentration of the green synthesized nanoparticles on the effective thermal diffusivity values of the nanofluids.

Effect of Annealing Temperature on the Thermo‐Optic Properties of Holmium Doped Silica Glasses Prepared by Sol‐Gel Method

Silica based glasses activated by rare earth ions promises to be an efficient material for the photonics applications. Incorporation of holmium as a rare earth dopant finds wide applications in the infrared range of the electromagnetic spectrum. In this work, we report the preparation and the thermo‐optic characterization of the holmium doped silica glasses. The samples are prepared via sol‐gel route. The structural characterization of the samples is carried out using the X‐ray diffraction technique whereas the constituents of the samples are identified using the Fourier Transform Infrared (FTIR) Spectroscopy. The optical properties of the samples are measured using the UV‐VIS absorption spectroscopy. The thermal effusivity values of the samples are evaluated using an open cell photoacoustic technique. Influence of the annealing temperature on the thermal as well as the optical properties of the samples is investigated in detail. Analysis of the results shows that the doping and annealing process influenc...

Thermal characterization of nanofluids using laser induced thermal lens technique

A laser induced thermal lens technique has been employed to evaluate the dynamic thermal parameter, the thermal diffusivity, of gold nanofluids. Gold nanoparticles were synthesized by citrate reduction of HAuCl4 in water. The UVVIS optical absorption spectra show an absorption peak around 540 nm owing to surface Plasmon resonance band of the gold particles. The thermal diffusivity of gold nanoparticles was evaluated by knowing the time constant of transient thermal lens obtained by fitting the experimental curve to the theoretical model of the mode-matched thermal lens. Analyses of the results show that the nanofluid exhibits lower thermal diffusivity value in comparison to the host medium, water. Further investigations also reveal that the concentration of nanoparticles in the fluid have influence on the measured thermal diffusivity value. Results are interpreted in terms of interfacial thermal resistance around the nanoparticles as well as on the clustering of nanoparticles.

Application of laser beam deflection technique to study the diffusion process in electrolyte solutions

A simple method based on laser beam deflection to study the variation of diffusion coefficient with concentration in a solution is presented. When a properly fanned out laser beam is passed through a rectangular cell filled with solution having concentration gradient, the emergent beam traces out a curved pattern on a screen. By taking measurements on the pattern at different concentrations, the variation of diffusion coefficient with concentration can be determined.