Plasma generated by fundamental radiation from a Nd:YAG laser focused onto a graphite target is studied spectroscopically. Measured line profiles of several ionic species were used to infer electron temperature and density at several sections located in front of the target surface. Line intensities of successive ionization states of carbon were used for electron temperature calculations. Stark broadened profiles of singly ionized species have been utilized for electron density measurements. Electron density as well as electron temperature were studied as functions of laser irradiance and time elapsed after the incidence of laser pulse. The validity of the assumption of local thermodynamic equilibrium is discussed in light of the results obtained. © 1997 American Institute of Physics. ͓S0021-8979͑97͒04116-9͔

Intra-excitonic relaxation dynamics in ZnO Appl. Phys. Lett. 99, 231910 (2011) Thermal diffusion of nitrogen into ZnO film deposited on InN/sapphire substrate by metal organic chemical vapor deposition J. Appl. Phys. 110, 113509 (2011) Manifestation of spin-spin interaction between oxygen vacancy and magnesium in ZnMgO nanorods by electron paramagnetic resonance studies Appl. Phys. Lett. 99, 194101 (2011) Selective pair luminescence in the 1.4-eV band of CdTe:In J. Appl. Phys. 110, 093103 (2011) Evidence of cation vacancy induced room temperature ferromagnetism in Li-N codoped ZnO thin films Appl. Phys. Lett. 99, 182503 (2011) Additional information on J. Appl. Phys. In this article we present size dependent spectroscopic observations of nanocolloids of ZnO. ZnO is reported to show two emission bands, an ultraviolet ͑UV͒ emission band and another in the green region. Apart from the known band gap 380 nm and impurity 530 nm emissions, we have found some peculiar features in the fluorescence spectra that are consistent with the nanoparticle size distribution. Results show that additional emissions at 420 and 490 nm are developed with particle size. The origin of the visible band emission is discussed. The mechanism of the luminescence suggests that UV luminescence of ZnO colloid is related to the transition from conduction band edge to valence band, and visible luminescence is caused by the transition from deep donor level to valence band due to oxygen vacancies and by the transition from conduction band to deep acceptor level due to impurities and defect states. A correlation analysis between the particle size and spectroscopic observations is also discussed.

TiO(2) colloidal nanoparticles and nanocrystals are prepared by hydrolysis of titanium isopropoxide employing a surfactant-free synthetic hydrothermal method. The synthesized samples are characterized by X-ray diffraction (XRD), HRTEM and FTIR. The XRD study confirms that the size of the colloidal nanoparticle is around 4 nm which the HRTEM analysis indicates the sizes of the colloidal nanoparticles are in the range of 2.5 nm. The fluorescence property of the TiO(2) colloidal nanoparticles studied by the emission spectrum confirms the presence of defect levels caused by the oxygen vacancies. We have observed new emission bands at 387 nm,421 nm, 485 nm, 530 nm and 574 nm wavelengths, first one (387 nm) being emission due to annihilation of excitons while remaining four could be arising from surface states. The emission spectrum of annealed nanocrystallites is also having these four band emissions. It is observed that the surface state emission basically consists of two categories of emission.

The effect of ambient gas on the dynamics of the plasma generated by laser ablation of a carbon target using 1.06 μm radiation from a Q-switched Nd:YAG laser has been investigated using a spectroscopic technique. The emission characteristics of the carbon plasma produced in argon, helium and air atmospheres are found to depend strongly on the nature and pressure of the surrounding gas. It has been observed that hotter and denser plasmas are formed in an argon atmosphere rather than in helium or air as an ambient.

Laser ablation of graphite has been carried out using 1.06 m radiation from a Q-switched Nd:YAG laser and the time of flight distribution of molecular C 2 present in the resultant plasma is investigated in terms of distance from the target as well as laser fluences employing time resolved spectroscopic technique. At low laser fluences the intensities of the emission lines from C 2 exhibit only single peak structure while beyond a threshold laser fluence, emission from C 2 shows a twin peak distribution in time. The occurrence of the faster velocity component at higher laser fluences is explained as due to species generated from recombination processes while the delayed peak is attributed to dissociation of higher carbon clusters resulting in the generation of C 2 molecule. Analysis of measured data provides a fairly complete picture of the evolution and dynamics of C 2 species in the laser induced plasma from graphite.

Spectroscopic studies of laser-induced plasma from a high-temperature superconducting material, viz., YBa2Cu3O7 (YBCO), have been carried out. Electron temperature and electron density measurements were made from spectral data. The Stark broadening of emission lines was used to determine the electron density, and the ratio of line intensities was exploited for the determination of electron temperature. An initial electron temperature of 2.35 eV and electron density of 2.5 × 1017 cm−3 were observed. The dependence on electron temperature and density on different experimental parameters such as distance from the target, delay time after the initiation of the plasma, and laser irradiance is also discussed in detail.

Solid-immersion-lens-enhanced nonlinear frequency-variation mapping of a silicon integrated-circuit Appl. Phys. Lett. 99, 193103 (2011) A microfiber cavity with minimal-volume confinement Appl. Phys. Lett. 99, 051105 (2011) Lead silicate glass microsphere resonators with absorption-limited Q Appl. Phys. Lett. 98, 181105 (2011) Full band structure calculation of two-photon indirect absorption in bulk silicon Appl. Phys. Lett. 98, 131101 (2011) Geometry and quadratic nonlinearity of charge transfer complexes in solution: A theoretical study J. Chem. Phys. 134, 044534 (2011) Additional information on J. Appl. Phys. We have investigated the third-order nonlinearity in ZnO nanocolloids with particle sizes in the range 6-18 nm by the z-scan technique. The third-order optical susceptibility ͑3͒ increases with increasing particle size ͑R͒ within the range of our investigations. In the weak confinement regime, an R 2 dependence of ͑3͒ is obtained for ZnO nanocolloids. The optical limiting response is also studied against particle size.

Silver nano-colloid was prepared by chemical reduction method and its nonlinear absorption properties were investigated by using open aperture z-scan experiment with nanosecond laser pulses operating at 532 nm. Interestingly, a switch over from saturable absorption to reverse saturable absorption was observed when the input intensity is increased from 28.1 to 175.8 MW/cm 2 . The underlying mechanism responsible for the observed switching behaviour is the interplay between ground state plasmon band bleaching and excited state absorption. Theoretical fitting was done by using a model in which nonlinear absorption coefficient as well as saturation intensity are incorporated.