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Time of ight emission spectroscopy of laser produced nickel plasma: Short-pulse and ultrafast excitations
No full textOpen AccessWe report the experimental investigation and comparison of the temporal features of short-pulse (7 ns) and ultrafast (100 fs) laser produced plasmas generated from a solid nickel target, expanding into a nitrogen background. When the ambient pressure is varied in a large range of 10−6 Torr to 102 Torr, the plume intensity is found to increase rapidly as the pressure crosses 1 Torr. Time of flight (TOF) spectroscopy of emission from neutral nickel (Ni I) at 361.9 nm (3d 9(2D) 4p → 3d 9(2D) 4s transition) reveals two peaks (fast and slow species) in short-pulse excitation and a single peak in ultrafast excitation. The fast and slow peaks represent recombined neutrals and un-ionized neutrals, respectively. TOF emission from singly ionized nickel (Ni II) studied using the 428.5 nm (3p63d8(3P) 4s→ 3p63d9 4s) transition shows only a single peak for either excitation. Velocities of the neutral and ionic species are determined from TOF measurements carried out at different positions (i.e., at distances of 2 mm and 4 mm, respectively, from the target surface) on the plume axis. Measured velocities indicate acceleration of neutrals and ions, which is caused by the Coulomb pull of the electrons enveloping the plume front in the case of ultrafast excitation. Both Coulomb pull and laser-plasma interaction contribute to the acceleration in the case of short-pulse excitation. These investigations provide new information on the pressure dependent temporal behavior of nickel plasmas produced by short-pulse and ultrafast laser pulses, which have potential uses in applications such as pulsed laser deposition and laser-induced nanoparticle generation
Long-range polarimetric imaging through fog.
No full textRestricted Access.We report an experimental implementation of long-range polarimetric imaging through fog over kilometric distance in real field atmospheric conditions. An incoherent polarized light source settled on a telecommunication tower is imaged at a distance of 1.3 km with a snapshot polarimetric camera including a birefringent Wollaston prism, allowing simultaneous acquisition of two images along orthogonal polarization directions. From a large number of acquisitions datasets and under various environmental conditions (clear sky/fog/haze, day/night), we compare the efficiency of using polarized light for source contrast increase with different signal representations (intensity, polarimetric difference, polarimetric contrast, etc.). With the limited-dynamics detector used, a maximum fourfold increase in contrast was demonstrated under bright background illumination using polarimetric difference image
Anomalous growth of multi-phased and multi-dimensional Manganese oxide–Metal (Fe, Co and Ni) oxide nanostructures: Synthesis and optical limiting properties
No full textRestricted Access.A single step approach toward the hydrothermal synthesis of Manganese oxide–Metal (Fe, Co and Ni) oxide nanocomposites (Mn–O, Fe–MnO, Co–MnO and Ni–MnO) is demonstrated. The composites are prepared using precursors such as potassium permanganate, urea and metal chlorides which are abundant in nature, making this a cost effective and environmentally benignant synthetic route. An anomalous growth was observed in the prepared composites, which had a minimum of two major phases with two different morphologies such as nanowires, nanorods, nanoplates and nanosheets. Growth mechanism of the composite nanostructures is predicted from morphological characterizations. Linear optical studies reveal the broad band visible light absorbance of the composites. Open aperture z-scan experiments are conducted at 532 nm using 5 ns laser pulses to study the optical limiting properties of the composites. The anomaly observed in the growth, demonstrates the possibility of fabricating multi-phased composites with multi-dimensional nanostructures, which can be employed in the cost effective design and development of optical limiters and sensors based on manganese and other transition metal oxides
The Koslowski–Sahlmann representation: quantum configuration space
No full textOpen Access - IOP selectThe Koslowski-Sahlmann (KS) representation is a generalization of therepresentation underlying the discrete spatial geometry of Loop Quantum Gravity(LQG), to accommodate states labelled by smooth spatial geometries. As shownrecently, the KS representation supports, in addition to the action of theholonomy and flux operators, the action of operators which are the quantumcounterparts of certain connection dependent functions known as "backgroundexponentials". Here we show that the KS representation displays the following propertieswhich are the exact counterparts of LQG ones: (i) the abelian algebra of holonomies and `' background exponentials can be completed to a algebra (ii) the space of semianalytic connections istopologically dense in the spectrum of this algebra (iii) there exists ameasure on this spectrum for which the KS Hilbert space is realised as thespace of square integrable functions on the spectrum (iv) the spectrum admits acharacterization as a projective limit of finite numbers of copies of and (v) the algebra underlying the KS representation is constructed fromcylindrical functions and their derivations in exactly the same way as the LQG(holonomy-flux) algebra except that the KS cylindrical functions depend on theholonomies and the background exponentials, this extra dependence beingresponsible for the differences between the KS and LQG algebras. While these results are obtained for compact spaces, they are expected to beof use for the construction of the KS representation in the asymptotically flatcase
Sol–gel prepared Cu2O microspheres: linear and nonlinear optical properties
No full textRestricted Access.We report the simple sol–gel based synthesis of size-tunable monodispersed crystalline Cu2O microspheres (CMS) and the measurement of their linear and nonlinear optical properties. Optical absorption spectra show a broad plasmonic absorption band extending from 350 to 1100 nm in general agreement with calculations based on Mie theory, despite the relatively large micron size of the particles. Z-scan measurements (532 nm, 5 ns pulses) reveal that Cu2O microspheres are efficient optical limiters, comparable in strength to nanocarbons and metal/semiconductor nanoparticles. The effective two-photon absorption coefficients are numerically calculated from measured data. These can be tuned systematically by varying the particle size
Variations in the pulsation and spectral characteristics of OAO 1657-415
No full textOpen Access.We present broad-band pulsation and spectral characteristics of the accreting X-ray pulsar OAO 1657−415 with a 2.2 d long Suzaku observation carried out covering its orbital phase range ∼0.12–0.34, with respect to the mid-eclipse. During the last third of the observation, the X-ray count rate in both the X-ray Imaging Spectrometer (XIS) and the HXD-PIN instruments increased by a factor of more than 10. During this observation, the hardness ratio also changed by a factor of more than 5, uncorrelated with the intensity variations. In two segments of the observation, lasting for ∼30–50 ks, the hardness ratio is very high. In these segments, the spectrum shows a large absorption column density and correspondingly large equivalent widths of the iron fluorescence lines. We found no conclusive evidence for the presence of a cyclotron line in the broad-band X-ray spectrum with Suzaku. The pulse profile, especially in the XIS energy band, shows evolution with time but not so with energy. We discuss the nature of the intensity variations, and variations of the absorption column density and emission lines during the duration of the observation as would be expected due to a clumpy stellar wind of the supergiant companion star. These results indicate that OAO 1657−415 has characteristics intermediate to the normal supergiant systems and the systems that show fast X-ray transient phenomena
Effect of dispersion of gold nanoparticles on the optical and electrical properties of discotic liquid crystal
No full textRestricted Access.Dispersion of gold nanoparticles (GNPs) in mononitro-substituted triphenylene-based discotic liquid crystal (DLC), which shows columnar plastic phase (Colp) along with columnar hexagonal phase (Colh) at room temperature, was studied by differential scanning calorimetry, polarising optical microscopy, X-ray diffraction, dielectric spectroscopy, visible absorbance spectroscopy and IR dichroic technique. The experimental results show that inclusion of GNPs in the DLC matrix strains the columnar matrix. More ordered Colp which possesses high charge carrier mobility because of the three-dimensional positional order is still preserved even by insertion of GNPs into the columnar matrix. However, we observed a decrease in orientational order parameter (S) and increase in relaxation time (τ) for disc motion with GNPs in Colp. But there is enhancement in dc electrical conductivity by several orders of magnitude at ambient conditions with GNPs. These GNP–DLC composite systems hold great promises in many organic semiconductor device applications
Energy dependent saturable and reverse saturable absorption in cube-like polyaniline/polymethyl methacrylate film
No full textRestricted Access.Solid films of cube-like polyaniline synthesized by inverse microemulsion polymerization method have been fabricated in a transparent PMMA host by an in situ free radical polymerization technique, and are characterized by spectroscopic and microscopic techniques. The nonlinear optical properties are studied by open aperture Z-scan technique employing 5 ns (532 nm) and 100 fs (800 nm) laser pulses. At the relatively lower laser pulse energy of 5 μJ, the film shows saturable absorption both in the nanosecond and femtosecond excitation domains. An interesting switchover from saturable absorption to reverse saturable absorption is observed at 532 nm when the energy of the nanosecond laser pulses is increased. The nonlinear absorption coefficient increases with increase in polyaniline concentration, with low optical limiting threshold, as required for a good optical limiter