No abstract

The dual-beam thermal lens technique has been found to be very effective for the measurement of fluorescence quantum yields of dye solutions. The concentration-dependence of the quantum yield of rhodamine B in methanol is studied here using this technique. The observed results are in line with the conclusion that the reduction in the quantum yield in the quenching region is essentially due to the non-radiative relaxation of the absorbed energy. The thermal lens has been found to become abberated above 40 mW of pump laser power. This low value for the upper limit of pump power is due to the fact that the medium is a resonantly absorbing one.

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.

We propose and demonstrate the possibility of using a permanently microbent bare optical fiber for detecting chemical species. Two detection schemes, viz., a bright-field detection scheme (for the core modes), and a dark-field detection scheme (for the cladding modes) have been employed to produce a fiber-optic sensor. The sensor described here is sensitive enough to detect concentrations as low as nanomoles per liter of a chemical species, with a dynamic range of more than 6 orders of magnitude.

Dual beam thermal lens tecbnique is successfully employe" for the determillatiolL of absolute Iluowscence quantum yield of rhodamine 6G lnser dye iu different solve"ts. A 532 IllU ra

The fabrication and characterization of a fibre optic pH sensor based on evanescent wave absorption is presented. The unclad portion of a multi-mode optical fibre is coated with a pH sensitive dye, which is immobilized by the sol-gel route. The sensitivity of the device has been found to increase when multiple sol-gel coatings are used as the sensing region. The dynamic range and the temporal response of the sensor are investigated for two different dyes, namely bromocresol purple and bromocresol green. The performance of the device is evaluated in terms of the results obtained during actual measurements.

Silver/titanium dioxide nanoparticles with varied concentration of silver have been synthesized by a simple laser light induced chemical reaction, where bulk titanium dioxide powder is used as the starting material. The particle size, morphology, crystal structure, and optical properties were characterized by transmission electron microscopy, x-ray diffraction, UV-Vis absorption spectroscopy, fluorescence spectroscopy, and Fourier transform infrared spectroscopy. The x-ray diffraction pattern revealed that the TiO2 nanoparticles obtained are in pure rutile phase. The important observation from transmission electron microscopic images is that the Ag particles are distributed over the surface of titanium dioxide nanoparticles. The band gap of the TiO2 nanoparticles was tuned between 1.75 and 2.75 eV by varying Ag concentration. The nonlinear optical absorption and optical limiting performance of Ag:TiO2 nanocomposites were investigated by open aperture z-scan using nanosecond Nd:YAG laser pulses operating at 532 nm. The best optical limiting threshold obtained was 113MW/cm2.

'The fabrication and characterization of a Rhodamine 6G-doped polymer optical fiber amplifier have befII carried out. Two different schemes were employed to characterize the optical fiber: the stripe illuminatioII technique to study the fiber as a gain medium and another technique to study its performance as III amplifier. We observed a spectral narrowing from 42 to 7 nm when the pump energy was increased ID 6 mJ in the stripe illumination geometry. A gain of 18 dB was obtained in the amplifier configuration. The effects of pump power and dye concentration on the performance of the fiber as an amplifier were alIu studied.