A. Mujeeb

Variations in fluorescence quantum yield of basic fuchsin with silver nanoparticles prepared by femtosecond laser ablation

Nano structured noble metals have very important applications in diverse fields such as photovoltaics, catalysis, electronic and magnetic devices, etc. In the present work, the application of dual beam thermal lens technique is employed for the determination of the absolute fluorescence quantum yield of the triaminotriphenylmethane dye, basic fuchsin in the presence of silver sol is studied. Silver sol is prepared by femtosecond laser ablation. It is observed that the presence of silver sol decreases the fluorescence quantum efficiency. The observed results are in line with the conclusion that the reduction in quantum yield in the quenching region is essentially due to the non-radiative relaxation of the absorbed energy. It is also observed that the presence of silver sol enhances the thermal lens signal which makes its detection easier at any concentration.

Measurement of absolute fluorescence quantum yield of basic Fuchsin solution using a dual-beam thermal lens technique.

The dual beam thermal lens technique is an effective method for the measurement of fluorescence quantum yield of dye solutions. The concentration-dependent quantum yield of a novel dye of triaminotriphenylmethane family in ethanol is studied using this technique. The absolute fluorescence quantum yield is measured and is observed that the reduction in the quantum yield is due to the non-radiative relaxation of the absorbed energy.

Electronic and optical properties of TiO2 and its polymorphs by Z-scan method

TiO2 is a material which has attracted considerable attention from the scientific community for its innumerable properties. TiO2 is known to exist in nature in three different crystalline structures: rutile, anatase, and brookite. Anatase and rutile TiO2 films have been widely characterized for their potential applications in solar cells, self-cleaning coatings, and photocatalysis. In the present report, the third-order nonlinear susceptibilities of TiO2 and its polymorphs, anatase, and rutile, prepared by the sol—gel technique followed by heat treatment are investigated using the Z-scan technique at a wavelength of 532 nm with a duration of 7 ns. Imaginary and real values of χ(3) for amorphous, anatase, and rutile are also calculated and found to be 5 × 10−19 m2/V2, 27 × 10−19 m2/V2, 19 × 10−19 m2/V2, respectively. It is found that the values of the optical constants of amorphous TiO2 after heat treatment vary considerably. It is assumed that this could be due to the variation in the electronic structure of TiO2 synchronous with the formation of its polymorphs, anatase, and rutile. Amorphous TiO2 is marked by the localization of the tail states near the band gap, whereas its crystalline counterparts are characterized by completely delocalized tail states.

Tailoring optical properties of TiO2 in silica glass for limiting applications

We present the linear and nonlinear optical studies on TiO2−SiO2 nanocomposites with varying compositions. Optical band gap of the material is found to vary with the amount of SiO2 in the composite. The phenomenon of two-photon absorption (TPA) in TiO2/SiO2 nanocomposites has been studied using open aperture Z-scan technique. The nanocomposites show better nonlinear optical properties than pure TiO2, which can be attributed to the surface states and weak dielectric confinement of TiO2 nanoparticles by SiO2 matrix. The nanocomposites are thermally treated and similar studies are performed. The anatase form of TiO2 in the nanocomposites shows superior properties relative to the amorphous and rutile counterpart. The involved mechanism is explained by rendering the dominant role played by the excitons in the TiO2 nanoparticles.

Stability, Size and Optical Properties of Silver Nanoparticles Prepared by Femtosecond Laser Ablation

Stability, Size and Optical Properties of Silver Nanoparticles Prepared by Femtosecond Laser Ablation Colloidal solutions of silver NPs were prepared in liquid environments by ablation of the silver target with femtosecond laser pulses at 800 nm. Resultant colloidal solutions were characterized by absorption spectroscopy, single beam zscan technique and electron microscopic techniques. The absorption peak was around 400nm and the average particle size obtained was 7nm. The resultant colloidal NPs in distilled water shows the highest stability.

Analysis of Various Surface Roughness Parameters of Low ModulusAerospace Materials Using Speckle Photography

Surface roughness is a principal measure of product quality of the materials used for sophisticated applications. The present paper reports an experimental investigation of various parameters related to the surface roughness of the materials used for the aerospace applications by an inexpensive non-invasive technique known as speckle photography. Conventional non-destructive testing techniques such as X-Ray imaging, ultrasound scanning, microwave testing etc, have certain limitations on testing the surface characteristics of low modulus aerospace vehicle components. This paper explains characterization of surface roughness by analyzing certain roughness parameters such as intensity distribution, size distribution and contrast ratio of different low modulus materials used in aerospace applications. The optical setup employed for the work is simple and uses an inexpensive digital camera for grabbing the specimens under different static conditions

Solvent Dependency in the Quantum Efficiency of 4-[(4-Aminophenyl)-(4-imino-1-cyclohexa-2, 5- dienylidene) methyl] Aniline Hydrochloride.

In the present work dual beam thermal lens technique is used for studying the solvent dependency on the quantum efficiency of a novel dye used for biomedical applications. The role of solvent in the absolute fluorescence quantum yield of 4-[(4-Aminophenyl)-(4-imino-1-cyclohexa-2, 5- dienylidene) methyl] aniline hydrochloride is studied using thermal lens technique. It is observed that the variation in solvents and its concentration results considerable variations in the fluorescence quantum yield. These variations are due to the non-radiative relaxation of the absorbed energy and because of the different solvent properties. The highest quantum yield of the dye is observed in the polar protic solvent-water.

Intensity and composition-dependent sign reversal of non-linearity in TiO2/CeO2 nanocomposites

CeO2/TiO2 composite nanoparticles with different Ce/Ti molar ratios have been successfully synthesized via sol—gel method. It was found that the band gap of the nanocomposite is tunable by varying Ce/Ti content. The nonlinear response of the sample was studied by using the nanosecond laser pulses from a Q switched Nd:Yag laser employing the Z-scan method. Open aperture Z-scan experiment revealed that with the increase in the CeO2 amount in the nanocomposite, the non-linearity of the composite increases, and it was assumed that this could be due to the modification of TiO2 dipole symmetry by the addition of CeO2. Closed aperture Z-scan experiment showed that when the CeO2 amount increases, positive nonlinear refraction decreases, and this could be attributed to the increase in the two photon absorption which subsequently suppresses the nonlinear refraction.

Detection and analysis of micro cracks in low modulus materials with thermal loading using laser speckle interferometry

Micro-defect detection is an essential field of failure analysis for the assessment and reliability of engineering materials under various loading conditions. This paper illustrates the effect of thermal loading on micro crack formation in certain low modulus materials used for aerospace applications and further analysis. The demands of increased performance of polymeric materials have created a need for new experimental techniques for accurate measurements of their structural defects through non-destructive ways. The present work employs one such optical non-destructive technique such as Laser Speckle Interferometry (LSI) to study the micro crack formation in the low modulus material used as an insulator in solid rocket motors. The low modulus material used is a nitrile based rubber compound which, when thermally loaded to a differential temperature in the range of 20°C to 28°C generates an optimum fringe pattern for the analysis of defects. Extremely small defects in the micrometer scale can be detected by analyzing the anomalies in the generated fringe pattern.

Power and composition dependent non linear optical switching of TiO 2 -SiO 2 nano composites

Linear as well as nonlinear absorption of TiO2-SiO2 nanocomposites prepared by sol gel process has been reported. To investigate the nonlinear properties, Z Scan technique was employed with 532 nm as the excitation wavelength followed by the calculation of the nonlinear optical constants. Z-scan experiments showed that when the excitation energy increased, the nonlinear absorption of the nanocomposites changed from reverse-saturable absorption to saturable absorption and then again back to reverse saturable absorption. Such a changeover in the sign of the nonlinearity is related to the interplay of exciton bleach and optical limiting mechanisms. The observed nonlinear absorption is found to be due to two photon absorption. The enhancement of the third-order nonlinearity in the composites can be due to the concentration of exciton oscillator strength.