[en] We report a well resolved whispering gallery mode (WGM) laser emission from a free-standing microring cavity based on a dye doped hollow polymer optical fiber (DDHPOF), which is transversely pumped by a pulsed Nd:YAG laser. The microring laser is characterized by a well-defined, low threshold pump power at which the emission spectral intensity dramatically increases and collapses into several dominant microcavity laser modes with reduced mode spacing and high Q-value. Resonant modes are excited inside the gain medium which is strongly confined along the radial direction so that the spacing of lasing modes is controlled by the diameter of the cylindrical microcavity. A variation in the free spectral range of WGM spectra from 0.23 to 0.09 nm coupled with a red-shift is observed with an increase in the diameter of DDHPOFs. - Highlights: • Different diameter free-standing cylindrical microcavity lasers have been fabricated and their performances have been evaluated. • The microring laser is characterized by a well-defined, low threshold pump power, with reduced mode spacing and high Q-value. • When the diameter of DDHPOF increases, the number of lasing peaks increases along with the decrease of the FSR as observed from our studies. • It is also found that whispering gallery lasing envelope is shifted from 559 to 571 nm (Stokes shift) with the diameter

[en] Highlights: • Silver nanospheres are synthesised in ethanol containing Poly Vinyl Pyrrolidone which acts as a polymeric capping agent to nanoparticles thus improving its stability. • Laser irradiation onto the colloidal solution of silver nanoparticles produced well defined nanowires through ripening mechanism promoted by Poly Vinyl Pyrrolidone. • Nanowires so formed are having an average length of 8.7 μm and width of 160 nm. - Abstract: Stable uniform silver nanospheres having an average diameter of 45 nm are synthesised in ethanol containing Poly Vinyl Pyrrolidone using Laser Ablation in Liquid technique. Further irradiation of the nanocolloidal solution by focussed laser beam produced stable well defined silver nanowires through ripening mechanism fostered by the presence of Poly Vinyl Pyrrolidone. Confirmation of the mechanism is obtained from Transmission Electron Microscopic images of the nanocolloidal solution irradiated for different time durations

[en] Photothermal phaseshift spectroscopy has been utilized for the study of laser ablation process. Values of laser induced damage and ablation threshold fluences during Nd:YAG laser interaction with superconducting ceramic materials YBa₂Cu₃O₇ and NdBa₂Cu₃O₇ were evaluated. Line averaged electron densities of laser induced plasma were found out. (author). 5 refs., 3 figs

[en] Laser induced plasma emission spectra from high Tsub(c) superconducting samples of YBa₂Cu₃O₇ and GdBa₂Cu₃O₇ obtained with 1-06 μm radiation from a Q switched Nd:YAG laser beam has been analysed. The results clearly show the presence of diatomic oxides in addition to ionized species of the constituent metals in the plasma thus produced. (author). 3 figs., 9 refs

[en] The spectroscopic analysis of the emission from the plasma produced by irradiating a high T_c superconducting GdBa₂Cu₃O₇ target with a high power Nd:YAG laser beam shows the existence of the bands from different oxides in addition to the lines from neutrals and ions of the constituent elements. The spectral emissions by oxide species in laser-induced plasma show considerable time delays as compared to those from neutral and ionic species. Recombination processes taking place during the cooling of the hot plasma, rather than the plasma expansion velocities, have been found to be responsible for the observed time delays in this case. The decays of emission intensities from various species are found to be non-exponential. (author). 8 refs., 5 figs

[en] We report on the linear and nonlinear optical studies of TiO₂-CeO₂ nanocomposites. It was found that the band gap of the nanocomposite can be tuned by varying Ce/Ti content. Nonlinear absorption characteristics of these samples were studied by employing open aperture Z-scan technique using an Nd:YAG laser (532 nm, 7 ns, 10 Hz). It has been observed that as the CeO₂ amount increases, band gap of the nanocomposites decreases and the reason proposed for the change in band gap is the smudging of localised states of Ce³⁺ into the forbidden energy gap, thus acting as the intermediate state. Fluorescence studies confirmed the above argument. Nonlinear investigation revealed that with increase in the CeO₂ amount, the two-photon absorption coefficient increased due to the modification of TiO₂ dipole symmetry. Suitable candidature of the nanocomposites for the fabrication of nonlinear optical devices was proved by determining the optical limiting threshold. (orig.)

[en] Time of flight (TOF) distribution of YO in laser ablated plasma from superconducting sample (YBa₂Cu₃O₇) is studied using emission spectroscopy. Up to a short distance (<1.5 cm) from the target, TOF distributions show twin peaks. At greater distances (>1.5 cm) all of them exhibit single peak distribution. (author). 3 refs., 3 figs

[en] We present third-order optical nonlinear absorption in CdSe quantum dots (QDs) with particle sizes in the range of 4.16 5.25 nm which has been evaluated by the -scan technique. At an excitation irradiance of 0.54 GW/cm"2 the CdSe QDs exhibit reverse saturation indicating a clear nonlinear behavior. Nonlinearity increases with particle size in CdSe QDs within the range of our investigations which in turn depends on the optical band gap. The optical limiting threshold of the QDs varies from 0.35 GW/cm"2 to 0.57 GW/cm"2 which makes CdSe QDs a promising

[en] This study reports the sensing of micro viscosity variation of Styryl 7(LDS 750) dye in different solvents and biological samples through thermal lens and fluorescence lifetime techniques. Fluorescence properties of Styryl 7 dye in different solvents and with DNA-CTMA (deoxyribonucleic acid attached with cetyltrimethyl-ammonium cationic surfactant molecules) were measured using fluorescence lifetime technique. Fluorescence lifetime of Styryl 7 in different solvents are found to increase with the viscosity of the samples. With increase in weight percentage of DNA-CTMA, the fluorescence lifetime increases from 0.17 ns to1.47 ns. Lifetime studies confirm that Styryl 7 dye is a good fluorescent probe for detecting the micro viscosity of the samples. Thermal lens technique, which is an efficient probe to measure non-radiative relaxation route were used to measure the thermal diffusivity of Styryl 7 in different solvents and with varying weight percentage of DNA-CTMA. Thermal diffusivity of the samples are found to decrease with increase in solvent viscosity and increased weight percentage of DNA-CTMA

[en] 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.