Time evolution of the electron density and temperature in laser-produced plasmas from YBa2Cu3O7

Laser radiation at 1.06 µm from a pulsed Nd:YAG laser was focused onto a multielement YBa2Cu3O7 target in vacuum and the plasma thus generated was studied using time-resolved spectroscopic techniques. Line broadening of the Ba I emission line at 553.5 nm was monitored as a function of time elapsed after the incidence of a laser pulse on the target. Measured line profiles of barium species were used to infer the electron density and temperature, and the time evolution of these important plasma parameters has been worked out.

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.

A comparative study of energy transfer in dye mixtures in monomer and polymer matrices under pulsed laser excitation

This study was conducted to identify the concentration dependence of the operating wavelengths and the relative intensities in which a dye mixture doped polymer optical fibre can operate. A comparative study of the radiative and Forster type energy transfer processes in Coumarin 540:Rhodamine 6G, Coumarin 540:Rhodamine B and Rhodamine 6G:Rhodamine B in methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA) was done by fabricating a series of dye mixture doped polymer rods which have two emission peaks with varying relative intensities. These rods can be used as preforms for the fabrication of polymer optical fibre amplifiers operating in the multi-wavelength regime. The 445 nm line from an Nd:YAG pumped optical parametric oscillator (OPO) was used as the excitation source for the first two dye pairs and a frequency doubled Nd:YAG laser emitting at 532 nm was used to excite the Rh 6G:Rh B pair. The fluorescence lifetimes of the donor molecule in pure form as well as in the mixtures were experimentally measured in both monomer and polymer matrices by time-correlated single photon counting technique. The energy transfer rate constants and transfer efficiencies were calculated and their dependence on the acceptor concentration was analysed. It was found that radiative energy transfer mechanisms are more efficient in all the three dye pairs in liquid and solid matrices.

Time evolution of Nd:YAG laser-induced plasma from GdBa2Cu3O7 high-Tc superconductor

In order to characterise the laser ablation process from high-Tc superconductors, the time evolution of plasma produced by a Q-switching Nd:YAG laser from a GdBa2Cu3O7 superconducting sample has been studied using spectroscopic and ion-probe techniques. It has been observed that there is a fairly large delay for the onset of the emission from oxide species in comparison with those from atoms and ions of the constituent elements present in the plasma. Faster decay occurs for emission from oxides and ions compared with that from neutral atoms. These observations support the view that oxides are not directly produced from the target, but are formed by the recombination process while the plasma cools down. Plasma parameters such as temperature and velocity are also evaluated.