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Synthesis of titanium nanoparticles using pulsed laser ablation of titanium in de-ionized water and isopropanol is reported. In situ growth of nanoparticles was confirmed using Rayleigh scattering in liquid and air ambient. Nucleation and growth of nanoparticles in liquid ambient occurs much faster than in air. Synthesized nanoparticles were characterized using the x-ray diffraction, transmission electron microscopy and photoluminescence measurements. Nanoparticles thus produced are spherical in shape, have crystalline phase with size distribution 5-35 nm and the average size increases with the increase in laser fluence. The colloidal solutions of nanoparticles show broad photoluminescence emission in the range 300-500 nm on optical pumping with 266 nm. A comparative study of titanium plasma in liquid and air is reported to understand the formation of titanium nanoparticles from laser plasma confined in different ambient. [ABSTRACT FROM AUTHOR]

We report the synthesis of aluminum nanoparticles using pulsed laser ablation in water confined plasma. Nanoparticles have spherical shape and size distribution depends on laser fluence. Strong blue photoluminescence peaks at 405 nm (3.06 eV) and 430 nm (2.89 eV) due to oxygen deficient defects (F, F+, and F++ centers) is reported with different UV excitations. A comparative study of plasma in deionized water and air ambient reveals enhanced line broadening and higher electron density in water confined plasma compared to that in air, in agreement with radiative recombination model. The temporal dependence of spectral radiant energy density of plasma is also discussed. [ABSTRACT FROM AUTHOR]

The effect of the atomic mass of the ablating target on the formation and expansion of the interaction region in laterally colliding plasmas has been studied. Fast imaging and optical emission spectroscopy have been utilized as diagnostic tools to investigate the characteristic features of the seed plasma as well as interaction zone formed by different target materials (i.e., carbon, aluminium, and nickel). The present results reveal that dynamical, spectral, and geometrical features of the induced interaction zone depend on the mass of the ablated species and spatial separation between the interacting plumes. It has been observed that a sharp, intense, and more directional interaction zone is formed by the interaction of heavier plume species in comparison to that observed for a lighter atomic mass target. Further, the difference in the plasma parameters in seed and interaction regions are explained from the analysis of emission from both the regions for aluminium plasma. [ABSTRACT FROM AUTHOR]

The effects of mass and pressure of ambient gas on the propagation dynamics of two laser-blow-off plasma plumes created in close proximity are investigated. A time gated fast imaging technique is used for recording the images of the laterally colliding plumes under different experimental conditions. Pressure is varied from 0.1 to 3 mbar in three ambient, i.e., helium, neon, and argon. Emphasis is given on the nature of shock-shock interaction under different ambient conditions. It has been observed that the shock-velocity, shape, strength, and their interactions are strongly dependent on the mass and density of the ambient gases. The role of the interacting shocks and their subsequent reflections on the formation and geometrical shape of the interaction region in different ambient conditions is briefly described. [ABSTRACT FROM AUTHOR]

Interactions of two Li plasma plumes and shock waves are investigated at various pressures (~10-5 to 3 mbar) in the argon gas ambient. Fast imaging and optical emission spectroscopy are used to study the plume dynamics and characteristic emission of plasmas. The plasma plumes are created in laser-blow-off geometry. The expansion of plasma plumes in the ambient gas leads to the formation of an interaction zone. The formation of interaction zone is dependent on the ambient pressure and below a certain pressure, no significant change is observed in the shape and size of the interaction plasma. In the higher pressure, formation of interaction zone and its shape are dependent on ambient pressure. Dynamics of seed plasmas and interaction zone are also affected by the shock-shock interactions. The shock-shock interaction depends on the angle of incidence (α) between two shock waves at the initial time of interaction but as the plumes expand, the shock-shock interaction does not follow α dependence. [ABSTRACT FROM AUTHOR]

We demonstrate that spider draglines exhibit a fatigueless response in extreme cyclic torsion up to its breaking limit. The well defined Raman bands at 1095 and 1245 cm-1 shifted linearly towards lower wavenumbers versus increasing twist in both clockwise and counter-clockwise directions. Under thousands of continuous loading cycles of twist strain approaching its breaking limit, all the Raman bands were preserved and the characteristic Raman peak shifts were found to be reversible. Besides, nanoscale surface profile of the worked silk appeared as good as the pristine silk. This unique fatigueless twist response of draglines, facilitated by reversible deformation of protein molecules, could find applications in durable miniatured devices. [ABSTRACT FROM AUTHOR]

We report a systematic investigation of two plume interactions at different spatial separation (3-7 mm) in laser-blow-off. The plasmas plumes are created using Laser-blow-off (LBO) scheme of a thin film. The fast imaging technique is used to record the evolution of seed plasmas and the interaction zone which is formed as a result of interaction of the two seed plasmas. Time resolved optical emission spectroscopy is used to study evolution of optical emissions of the species present in the different regions of the plasmas. Neutral Li emissions (Li I 670.8 nm (2s ²S1/2 ← 2p ²P3/2,1/2) and Li I 610.3 nm (2p ²P3/2, 1/2 ← 3d ²D3/2, 5/2)) are dominant in the plasmas but significant differences are observed in the emission and estimated plasma parameters of the seed and the interaction zone. The transport of plasma species from the seed plasmas to the interaction zone is discussed in the terms of plume divergence, kinetic energy of particles, and ion acoustic speed. An attempt is made to understand the formation and dynamics of the interaction zone in the colliding LBO seed plasmas. [ABSTRACT FROM AUTHOR]

Dynamics of Li plasma plume created by laser-blow-off technique in air ambient is reported. Plasma plume dynamics and its optical emission are investigated in planar and confined geometries using time resolved shadowgraph imaging and optical emission spectroscopy. Significant differences in the plasma characteristics in confined geometry are quantitatively investigated by comparing the plasma parameters (temperature and density) in free expansion and confined geometry configurations. Dynamics and physical parameters of the primary as well as the reflected shock waves (in confined geometry) and their interactions with expanding plasma are briefly addressed. A large enhancement in the emission intensities of Li I 610.3 nm (2p 2P1/2, 3/2 ← 3d 2P3/2, 5/2) and 670.8 nm (2s 2S1/2 ← 2p 2P1/2, 3/2) is correlated with the shock wave dynamics in the two geometries. Strong self reversal in the neutral emission infers an increase in the population density of neutrals within the confined plasma plume. [ABSTRACT FROM AUTHOR]

The dynamics of copper ablated plasma plumes generated using laser ablation of copper targets in both liquid (de-ionized water) and gas (air) ambients is reported. Using time and space resolved visible emission spectroscopy (450-650 nm), the plasma plumes parameters are investigated. The electron density (ne) determined using Stark broadening of the Cu I (3d104d1 2D3/2-3d104p1 2P3/2 at 521.8 nm) line is estimated and compared for both plasma plumes. The electron temperature (Te) was estimated using the relative line emission intensities of the neutral copper transitions. Field emission scanning electron microscopy and energy dispersive x-ray spectral analysis of the ablated copper surface indicated abundance of spherical nanoparticles in liquid while those in air are amalgamates of irregular shapes. The nanoparticles suspended in the confining liquid form aggregates and exhibit a surface plasmon resonance at ∼590 nm. [ABSTRACT FROM AUTHOR]

We report the growth dynamics and confinement of nanoparticles in laser ablated titanium plasma in water cavitation and air ambient. The time resolved shadowgraphs are used to analyze the shockwave, cavitations, and dynamics of expanding plume in different ambient. The dynamical growth of nanoparticles is ascertained using the laser light scattering. Temporal evolution of plasma emission spectra and its parameters show distinct characteristic difference in the plasma confined in different ambient. The morphological characteristics of synthesized nanoparticles are ascertained using electron microscopy. A comparative study of plume dynamics, light scattering and optical emission of plasma in water and air ambient is used to corroborate the nanoparticle formation. [ABSTRACT FROM AUTHOR]

We investigate torsion mechanics of various spider silks using a sensitive optical technique. We find that spider silks are torsionally superelastic in that they can reversibly withstand great torsion strains of over 102-3 rotations per cm before failure. Among various silks from a spider, we find the failure twist-strain is greatest in the sticky capture silk followed by dragline and egg-case silk. Our in situ laser-diffraction measurements reveal that torsional strains on the silks induce a nano-scale transverse compression in its diameter that is linear and reversible. These unique torsional properties of the silks could find applications in silk-based materials and devices. [ABSTRACT FROM AUTHOR]