Riscob B.,National Physical Laboratory India |
Riscob B.,Jamia Millia Islamia University |
Bhatt R.,RRCAT |
Vijayan N.,National Physical Laboratory India |
And 5 more authors.
Journal of Applied Crystallography | Year: 2013
Zr-Fe-doped congruent lithium niobate single crystals were grown by the Czochralski technique. The crystal structure and lattice parameter of the grown crystals were assessed by powder X-ray diffraction and the strain developed as a result of doping has been calculated (-1.19 × 10-3) by using the Williamson-Hall relation. The incorporated dopant concentration along with the dopant distribution in the specimen crystal was estimated by X-ray florescence spectrometry. A multi-crystal X-ray diffraction analysis was carried out to identify the crystalline perfection of the sample and revealed that the investigated crystal does not contain any structural grain boundaries but does contain point defects and micrometre size mosaic blocks. Birefringence measurements were carried out using a prism coupler spectrometer and found that the optical birefringence is 0.0822 for 532nm and 0.705 for 1064nm. A thermal conductivity (κ) study reveals that the doped sample has a lower κ value than the undoped equivalent. © 2013 International Union of Crystallography.
Dwivedi R.,Devi Ahilya University |
Maurya A.,Dr Hari Singh Gour University |
Verma A.,Devi Ahilya University |
Prasad R.,Devi Ahilya University |
Journal of Alloys and Compounds | Year: 2011
A simple and fast synthesis of zirconia nanoparticles by microware assisted citrate sol-gel method is reported. The formation of nanoparticles was characterized by performing powder X-ray diffraction (XRD) of the samples calcined at higher temperatures. The physico-chemical characterizations were done employing techniques of Raman spectroscopy and BET surface area measurements. Fourier transform infrared spectroscopy (FTIR) was performed to analyze the band structure and functional groups. High-resolution transmission electron microscopy (HRTEM) was done for analyzing the morphology of nanoparticles and estimating the crystallite sizes. The prepared material was found to have tetragonal symmetry. The average particle sizes were found ranging ∼5-10 nm. Gelation and fast combustion seems to be the reason for smaller particle sizes. © 2011 Elsevier B.V. All rights reserved.
Rai V.N.,RRCAT |
Raja Sekhar B.N.,Bhabha Atomic Research Center |
Kher S.,Fiber Optics Laboratory |
Journal of Luminescence | Year: 2010
The effect of gamma irradiation in the dose range of 5-500 kGy on the optical absorption and luminescence spectra of Nd doped phosphate glass is reported. The spectral absorption of this glass before and after gamma irradiation was measured in the spectral range 300-900 nm at room temperature using spectrophotometer and synchrotron beamline. Drastic increase in absorption was noted below 600 nm after gamma irradiation, which was dependent on the dose of irradiation. Additional absorption (AA) spectra of irradiated sample shows generation of two absorption bands below 600 nm, which finally became one very broad band peak with increased intensity at irradiation dose of 500 kGy. AA spectra also show the presence of negative peaks at the location of absorption peaks of Nd3+. Photoluminescence of Nd doped phosphate glass shows two strong bands which decreases to a very low intensity with a red shift after gamma irradiation. These results indicate that irradiation produces different kinds of defects in the glass material along with conversion of valence state of Nd3+ to Nd2+. This change was found irreversible at room temperature. © 2009 Elsevier B.V. All rights reserved.
Sahani P.K.,RRCAT |
Haridas G.,Bhabha Atomic Research Center |
Sarkar P.K.,Bhabha Atomic Research Center
Indian Journal of Pure and Applied Physics | Year: 2012
Bremsstrahlung photons followed by photoneutrons are the major radiation hazards in high energy electron accelerators. These neutrons in high energy electron accelerator are produced by Bremsstrahlung photons through photo nuclear reactions. Monte Carlo code FLUKA was used to generate the photoneutron spectra for 20 MeV, 450 MeV and 2.5 GeV electron (electron energies in Indus facility) hitting 4 mm of tungsten target. The total photoneutron yield was calculated from the generated spectrum for different target thicknesses. The results have indicated the isotropic Giant Dipole Resonance (GDR) neutrons dominating the spectra for the above three incident electron energies. The peak energy of the neutron spectra lies between 0.1-1 MeV for these electron energies. The average neutron energy was calculated and found to be 0.82 MeV, 4.09 MeV and 11.6 MeV for 20 MeV, 450 MeV and 2.5 GeV incident electron energy, respectively. The details of the simulation and results are discussed in the paper.
Astadjov D.N.,Bulgarian Academy of Science |
Journal of Physics: Conference Series | Year: 2010
CuBr laser beam profile transformations are studied in a beam focusing experiment. A modeling via Fourier transform is also performed with annular beams of simplified flat two-level geometry of near field: bright outer ring with a darker core. The pattern of focal beam profile i.e. far field is calculated and characterized with respect of its intensity structure. As found beam annularity has small effect on far-field intensity pattern. © 2010 IOP Publishing Ltd.
Saini R.K.,Laser RandD |
Srivastava A.K.,RRCAT |
Gupta P.K.,Laser RandD |
Das K.,Laser RandD
Chemical Physics Letters | Year: 2011
Aggregation behaviour of Chitosan and glycol-Chitosan stabilized silver nanoparticles was investigated over the pH range of 3.4-13. With increasing pH, the charge of the particle reduces and approaches zero beyond 6.5 (the pK a of the amino group) inducing aggregation that was confirmed by absorption spectroscopy, hyper-Rayleigh scattering (HRS) and TEM measurements. Interestingly the HRS intensity increased till pH 9.0 ± 2.0 and beyond this it dropped dramatically. This correlated with the formation of centrosymmetric spherical aggregates as evidenced by TEM pictures. The aggregation process was found to be reversible over at least 10 pH cycles by absorption and HRS measurements. © 2011 Elsevier B.V. All rights reserved.
Sethi A.R.,Indian Institute of Technology Bombay |
Patel H.S.,RRCAT |
Srivastava A.,Indian Institute of Technology Bombay
Progress in Biomedical Optics and Imaging - Proceedings of SPIE | Year: 2013
We report the use of genetic algorithm-based approach for reconstruction of the optical inhomogeneities embedded in turbid medium using diffuse optical tomography. In the proposed inversion scheme, the task of image reconstruction is formulated as optimization (minimization) problem which is solved using genetic algorithm approach to find the global minimum of the objective function. This approach preserves the full non-linear features of the problem and it can be applied for quantitative reconstruction over a wide range of contrast values where conventional linear and higher order reconstruction approaches show severe limitations. Successful implementation of the proposed scheme has been demonstrated for quantitative reconstruction of absorbing inhomogeneities (single as well as double) embedded in an otherwise homogeneous medium. In order to demonstrate its potential, reconstruction results have been presented for a wide range of parameters including size, location and contrast of the absorbing inhomogeneities embedded in the turbid medium. © 2013 Copyright SPIE.
Prasad Y.B.S.R.,RRCAT |
Barnwal S.,RRCAT |
Naik P.A.,RRCAT |
Chakera J.A.,RRCAT |
And 2 more authors.
Applied Physics Letters | Year: 2010
The dynamics of ultrashort laser plasmas demand single shot temporal measurements on fast time scales. We describe a method to record the plasma expansion on picosecond (ps) timescales continuously over hundreds of ps, in single shot. The method uses the chirp of a Ti:sapphire laser as a time-resolved optical diagnostic tool. Using this technique, the evolution of the plasma expansion had been recorded with ps time resolutions, by probing with a chirped laser pulse of 200 ps duration. A peak expansion velocity of 1.8× 10 7cm/s is observed and its evolution in time is obtained for ∼300 ps. © 2010 American Institute of Physics.
Saini R.K.,RRCAT |
Gupta P.K.,RRCAT |
Journal of Molecular Structure | Year: 2012
Plasmon-molecular resonance coupling between Chlorine-p6 (Cp6) and poly-l-lysine stabilized silver nanoparticles (pLL-AgNP), both of which absorbs strongly at 400 nm, is reported. Resonance coupling results in a decrease in the intensity of the 400 nm band accompanied by a splitting. Coupling decreases at low pH due to partial neutralization of the charge of Cp6. The fluorescence intensity of Cp6 at pH 7 in the presence of pLL-AgNP gets drastically reduced which is attributed to the formation of non-fluorescent coupled states. The effect of only the polymer (poly-l-lysine) was also investigated. Spectroscopic studies suggest that polymer induces significant aggregation of Cp6 by electrostatic interaction. © 2012 Elsevier B.V. All rights reserved.
Reddi R.S.B.,Banaras Hindu University |
Ganesamoorthy S.,RRCAT |
Gupta P.K.,RRCAT |
Rai R.N.,Banaras Hindu University
Fluid Phase Equilibria | Year: 2012
The phase diagram of urea-4-bromo-2-nitroaniline system was studied which shows a large miscibility gap and the formation of a eutectic and a monotectic where the mole fractions of 4-bromo-2-nitroaniline are 0.899 and 0.020, respectively. The critical temperature is being 61.5 °C above the monotectic horizontal. The formation of solid solution of 4-bromo-2-nitroaniline in urea was studied by powder X-ray diffraction technique. Using differential scanning calorimetry (DSC), the enthalpies of fusion of the pure components, the eutectic and the monotectic were determined. The different thermodynamic parameters such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions were calculated utilizing the heat of fusion values. The solid-liquid interfacial energy has also been calculated and their effects on morphological change of microstructure of monotectic and eutectic have been discussed. © 2011 Elsevier B.V.