Department of Physics

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IIT Jodhpur

Investigations of a high resolution X-ray emission spectrum in the range 0.66-0.75 nm obtained by irradiating a Germanium target with high-power p-polarized, 40 picosecond laser radiation at 532 nm wavelength was done. Spectra in the wavelength region of 21-41′ and 21-51′ L-shell transitions in F-like, Ne-like and Na-like germanium ions were recorded using the FSSR-2D spectrometer equipped with a spherically bent quartz crystal with a spectral resolution λ/△λ better than 5000. Spectral lines were compared with theoretical values obtained using the LANL plasma kinetic code ATOMIC. Fair agreement between experimental and theoretical spectral lines has been observed, which allowed to measure enough high bulk electron temperature values of 560 eV and electron density of ∼ 1021 cm-3 in Ge plasma irradiated by rather small commercial high repetition rate Nd:YAG laser system. Copyright to 2007 Cambridge University Press.

World University root node

Laser and Particle Beams

High resolution X-ray emission spectra from picosecond laser irradiated Ge targets

We present a control system, which allows an automatic optimization of the pulse train stability in a mode-locked laser cavity. In order to obtain real-time corrections, we chose a closed loop approach. The control variable is the cavity length, mechanically adjusted by gear system acting on the rear cavity mirror, and the controlled variable is the envelope modulation of the mode-locked pulse train. Such automatic control system maintains the amplitude of the mode-locking pulse train stable within a few percent rms during the working time of the laser. Full implementation of the system on an Nd:yttrium lithium fluoride actively mode-locked laser is presented. © 2007 American Institute of Physics.

Fulltext

Review of Scientific Instruments

Mode-locking optimization with a real-time feedback system in a Nd:yttrium lithium fluoride laser cavity

The investigation addresses the electron transport properties of Co71-xFexCr7Si8B14 (x=0, 2, 3.2, 4, 6, 8 and 12 at%) amorphous alloys. The variation in electrical resistivity of as-cast amorphous materials with thermal scanning from room temperature to 1000 K was measured. The CoFe-based alloys revealed an initial decrease in temperature coefficient of resistivity (TCR), a characteristic of spin-wave phenomena in glassy metallic systems. This behaviour in the present alloys was in a sharp contrast to the Co-based amorphous materials that indicate the drop in resistivity much below room temperature. In the studied alloys, the variation in initial TCR values and the full-width at half-maxima determined from X-ray diffraction of as-quenched materials exhibited a similar trend with increasing Fe content, indicating the compositional effect of near neighbouring atoms. After the initial decrease in resistivity, all the alloys indicated a subsequent increase at Tmin. The Curie temperature (TC), which was measured from thermal variation of ac susceptibility showed non-monotonic change with Fe content. In the temperature range between Tmin and TC the relative scattering by electron-magnon and electron-phonon resulted in the non-monotonic change in Curie temperature. At crystallization onset (TX1) all the alloys except there with X=6, showed a sharp decrease in electrical resistivity which was attributed to ordering phenomena. In contrast to this resistivity decrease, X=6 alloy exhibited a drastic increase in resistivity around TX1 observed during amorphous to nanocrystalline transformation. Such nanocrystalline state was observed by Transmission electron microscopy. © 2006 Elsevier B.V. All rights reserved.

Journal of Magnetism and Magnetic Materials

Electron transport properties of Co71-xFexCr7Si8B14 (x=0, 2, 3.2, 4, 6,8 and 12 at%) amorphous alloys during devitrification

Magnetic hysteresis loop and Barkhausen emissions were recorded and analysed for 5Cr-0.5Mo steel after ageing at 600 °C for various lengths of time. At the initial stage of ageing the interstitial carbon diffuses towards the grain boundary making the matrix magnetically softer. During this stage, extending up to 200 h of ageing, magnetic softness was found to be increasing. This was associated with a decrease in coercivity and increase in Barkhausen voltage. Beyond 200 h of ageing the precipitation of alloy carbides attain subsequent growth, making the material magnetically harder. The evolution of carbides was studied using SEM-EDAX analysis. It was observed that most of the carbides transformed into M23C6 type after ageing for 400 h. © 2006.

NDT and E International

Ageing behavior study of 5Cr-0.5Mo steel by magnetic Barkhausen emissions and magnetic hysteresis loop techniques

A novel synthesis method is presented for the preparation of eco-friendly, doped semiconductor nanocrystals encapsulated within oxide-shells, both formed sequentially from a single-source solidprecursor. Highly luminescent ZnS nanoparticles, in situ doped with Cu +-Al 3+ pairs and encapsulated with ZnO shells are prepared by the thermal decomposition of a solid-precursor compound, zinc sulfato-thiourea-oxyhydroxide, showing layered crystal structure. The precursor compound is prepared by an aqueous wet-chemical reaction involving necessary chemical reagents required for the precipitation, doping and inorganic surface capping of the nanoparticles. The elemental analysis (C, H, N, S, O, Zn), quantitative estimation of different chemical groups (SO 4 2- and NH 4 -) and infrared studies suggested that the precursor compound is formed by the intercalation of thiourea, and/or its derivatives thiocarbamate (CSNH 2 -), dithiocarbamate (CS 2NH 2 -), etc., and ammonia into the gallery space of zinc-sulfato-oxyhydroxide corbel where the Zn II ions are both in the octahedral as well as tetrahedral coordination in the ratio 3:2 and the dopant ions are incorporated within octahedral voids. The powder X-ray diffraction of precursor compound shows high intensity basal reflection corresponding to the large lattice-plane spacing of d = 11.23 Å and the Rietveld analysis suggested orthorhombic structure with a = 9.71 Å, b = 12.48 Å, c = 26.43 Å, and β = 90°. Transmission electron microscopy studies show the presence of micrometer sized acicular monocrystallites with prismatic platy morphology. Controlled thermolysis of the solid-precursor at 70-110°C leads to the collapse of layered structure due to the hydrolysis of interlayer thiourea molecules or its derivatives and the S 2- ions liberated thereby reacts with the tetrahedral Zn II atoms leading to the precipitation of ZnS nanoparticles at the gallery space. During this process, the dopant ions situated at octahedral voids gets incorporated into the nano-ZnS lattice and results in bright photoluminescence. On further heat treatment above 1100°C, the corbel zinc-oxyhydroxide sheets undergo dehydroxylation to form ZnO which eventually encapsulates the ZnS nanoparticles at the gallery leading to significant enhancement in the luminescence quantum efficiency, up to ∼22%. The emission color of thus formed nano-ZnS/micro-ZnO composites could be tuned over wide spectral ranges from 480 to 618 nm and the spectral changes are attributed to a number of factors including lattice defects, Cu +-Al 3+ dopant-pairs and iso-electronic oxygen in nano-ZnS and oxygen-vacancy or -interstitial centers in non-stoichiometric ZnO. Copyright © 2007 American Scientific Publishers All rights reserved.

Journal of Nanoscience and Nanotechnology

A single-source solid-precursor method for making eco-friendly doped semiconductor nanoparticles emitting multi-color luminescence

We consider the teleportation of quantum information consisting of the quantum state of a set S1 of N two-level systems (TLSs), using EPR entangled state consisting of set S2 ⊕ S3 where set S2 has M TLSs and set S3 has N TLSs. The Bell state measurement is done on set S1 ⊕ S2 and a unitary transformation, dependent on this result, on the quantum state of set S 3 generates a replica of the original state of set S1. We show rigorously that the teleportation is possible only if M ≥ N. © World Scientific Publishing Company.

Modern Physics Letters B

A generalized condition for teleportation of the quantum state of an assembly of N two-level system

We study the dynamics of the quantum phase distribution associated with the reduced density matrix of a system for a number of situations of practical importance, as the system evolves under the influence of its environment, interacting via a quantum nondemolition type of coupling, such that there is decoherence without dissipation, as well as when it interacts via a dissipative interaction, resulting in decoherence as well as dissipation. The system is taken to be either a two-level atom (or, equivalently, a spin- 1 2 system) or a harmonic oscillator, and the environment is modeled as a bath of harmonic oscillators, starting out in a squeezed thermal state. The impact of the different environmental parameters on the dynamics of the quantum phase distribution for the system starting out in various initial states is explicitly brought out. An interesting feature that emerges from our work is that the relationship between squeezing and temperature effects depends on the type of system-bath interaction. In the case of a quantum nondemolition type of interaction, squeezing and temperature work in tandem, producing a diffusive effect on the phase distribution. In contrast, in the case of a dissipative interaction, the influence of temperature can be counteracted by squeezing, which manifests as a resistance to randomization of phase. We make use of the phase distributions to bring out a notion of complementarity in atomic systems. We also study the variance of the phase using phase distributions conditioned on particular initial states of the system. © 2007 The American Physical Society.

Physical Review A - Atomic, Molecular, and Optical Physics

Phase diffusion in quantum dissipative systems

In the scheme of a quantum nondemolition (QND) measurement, an observable is measured without perturbing its evolution. In the context of studies of decoherence in quantum computing, we examine the 'open' quantum system of a two-level atom or, equivalently, a spin-1/2 system, in interaction with quantum reservoirs of either oscillators or spins, under the QND condition of the Hamiltonian of the system commuting with the system-reservoir interaction. For completeness, we also examine the well-known non-QND spin-Bose problem. For all these many-body systems, we use the methods of functional integration to work out the propagators. The propagators for the QND Hamiltonians are shown to be analogous to the squeezing and rotation operators, respectively, for the two kinds of baths considered. Squeezing and rotation being both phase-space area-preserving canonical transformations, this brings out an interesting connection between the energy-preserving QND Hamiltonians and the homogeneous linear canonical transformations. © 2007 IOP Publishing Ltd.

Journal of Physics A: Mathematical and Theoretical

Functional integral treatment of some quantum nondemolition systems

We have fabricated and characterized photodetectors based on organic semiconductors. Concentration gradients of an electron-donor and an electron-acceptor were achieved between the two electrodes. Such gradients in the molecular scale, introduced via layer-by-layer electrostatic assembly, provided an extended region for exciton dissociation and bicontinuous pathways for carrier transport to the opposite electrodes. Results in the graded heterostructures have been compared with bulk-heterojunction devices. © 2006 Elsevier B.V. All rights reserved.

Materials Science and Engineering C

Organic photodetectors based on graded heterostructure of donor and acceptor layers

We have fabricated photodetectors based on electron-accepting and electron-donating organic materials. Multiple heterojunctions between the donor and acceptor layers were introduced. The thickness of the donor and acceptor materials was controlled in the molecular scale. By keeping the total thickness of the devices the same, we have studied the performance of the photodetectors as a function of the number of such molecular-level interfaces. The results showed that the number of donor-acceptor interfaces enhanced exciton dissociation but, at the same time, hindered charge transport by introducing energy barriers. We have shown that a trade-off between the two effects existed at an optimum number of donor-acceptor interfaces, where the device showed better photodetector performance. © 2006 Elsevier B.V. All rights reserved.