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Synthesis and optical limiting studies of HA(P) and HA(P)@SiO2 core-shell nanoparticles
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We report the spectral and optical limiting properties of two kinds of HAP nanoparticles (pure HAP and HAP@SiO2 core–shell nanoparticles) that were wet-chemically prepared and coated with silica by means of Stober method. The size, framework substitution and silica coating formation of the resultant particles were confirmed by Transmission Electron Microscopy, X-ray diffraction, Fourier Transform Infrared Spectroscopy and Thermogravimetric analysis. The nonlinear optical limiting properties of HAP and HAP@SiO2 nanoparticles suspended in ethylene glycol is studied at 532 nm using 5 ns Nd:YAG laser pulses. Observations indicate that effective three-photon absorption is found to be responsible for strong optical limiting characteristics in these nanoparticles and it is seen that the optical nonlinearity is enhanced in core–shell structures as compared with single counterparts. The nonlinear optical parameters calculated from the data show that these materials are efficient optical limiters
Achiral bent-core azo compounds: effect of different types of linkage groups and their direction of linking on liquid crystalline properties
No full textRestricted Access.We report, the design, synthesis and mesomorphic properties of six new homologous series of achiral bent-core compounds. In this study, we have investigated the effect of different types of linkage groups and their direction of linking, on the mesomorphic properties of azo functionalized compounds. The molecular structures of these newly synthesized compounds are characterized by spectroscopic methods. The liquid crystalline properties are studied using polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies. We observed a variety of mesophases in these compounds, viz. N, B1, B2, SmA, SmAdPAetc. From our investigations, we found that the type and the direction of the linkage group affects the thermal range or even sometimes the nature of the mesophase itself. We have also carried out photo-induced studies on the B2 mesophase of some of the selected compounds and found that the reversal in the direction of linkage groups does affect the photochromic properties of the compounds
Investigations of nonlinear optical effects and ultrafast laser Induced plasma in nanostructured media
No full textNon-local geometric phase in two-photon interferometry
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We report the experimental observation of the non-local geometric phase in Hanbury Brown-Twiss polarized intensity interferometry. The experiment involves two independent, polarized, incoherent sources, illuminating two polarized detectors. Varying the relative polarization angle between the detectors introduces a geometric phase equal to half the solid angle on the Poincaré sphere traced out by a pair of single photons. Local measurements at either detector do not reveal the effect of the geometric phase, which appears only in the coincidence counts between the two detectors, showing a genuinely non-local effect. We show experimentally that coincidence rates of photon arrival times at separated detectors can be controlled by the two-photon geometric phase. This effect can be used for manipulating and controlling photonic entanglement
Tuning DNA-amphiphile condensate architecture with strongly binding counterions
No full textRestricted Access.Electrostatic self-assembly of colloidal and nanoparticles has attracted a lot of attention in recent years, since it offers the possibility of producing novel crystalline structures that have the potential to be used as advanced materials for photonic and other applications. The stoichiometry of these crystals is not constrained by charge neutrality of the two types of particles due to the presence of counterions, and hence a variety of three-dimensional structures have been observed depending on the relative sizes of the particles and their charge. Here we report structural polymorphism of two-dimensional crystals of oppositely charged linear macroions, namely DNA and self-assembled cylindrical micelles of cationic amphiphiles. Our system differs from those studied earlier in terms of the presence of a strongly binding counterion that competes with DNA to bind to the micelle. The presence of these counterions leads to novel structures of these crystals, such as a square lattice and a Graphic superlattice of an underlying hexagonal lattice, determined from a detailed analysis of the small-angle diffraction data. These lower-dimensional equilibrium systems can play an important role in developing a deeper theoretical understanding of the stability of crystals of oppositely charged particles. Further, it should be possible to use the same design principles to fabricate structures on a longer length-scale by an appropriate choice of the two macroion
Combined ion and atom trap for low temperature ion-atom physics
No full textRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)We report an experimental apparatus and technique which simultaneously traps ions and cold atoms with spatial overlap. Such an apparatus is motivated by the study of ion–atom processes at temperatures ranging from hot to ultra cold. This area is a largely unexplored domain of physics with cold trapped atoms. In this article we discuss the general design considerations for combining these two traps and present our experimental setup. The ion trap and atom trap are characterized independently of each other. The simultaneous operation of both is then described and experimental signatures of the effect of the ions and cold atoms on each other are presented. In conclusion, the use of such an instrument for several problems in physics and chemistry is briefly discussed
Two distinct modulated layer structures of an asymmetric bent-shape smectic liquid crystal
No full textRestricted Access.We present chemical synthesis, polarising optical microscopy, electric current, and small-angle X-ray scattering measurements on a strongly anisotropic bent-shape liquid crystal material. We find that it has two layer-undulated ferroelectric phases, M1 and M2. In the higher temperature M2 phase the undulation amplitude and period increases on cooling, similar to other published materials. It can be identified with a tilted modulated phase. In the M1 phase the molecular plane is not tilted, and – in sharp contrast with all prior observations – the modulation amplitude and period decrease on cooling. These observations can be explained with a ‘leaning’ director structure, where the leaning angle is decreasing on cooling
Ethanol electrocatalysis on gold and conducting polymer nanocomposites: A study of the kinetic parameters
No full textRestricted Access.The study attempts to compare the electrocatalytic effect of gold nanoparticles dispersed conjugated polymers using activation energy, Tafel slopes and reaction orders for the evaluation of their performance. A simple and rapid in situ chemical and electrochemical method was adopted for the synthesis of gold and different conducting polymers nanocomposites on electrode surfaces. The method involves the polymerization of the monomer to yield the polymer nanocomposite film with dispersed gold nanoparticles. Polyaniline, polypyrrole, polythiophene and poly(3,4-ethylenedioxythiophene) are the four polymers studied in this work. A systematic comparison among the nanocomposites reveals that although all the conducting polymers have good catalytic activity in alkaline medium however polyaniline dispersed with gold nanoparticles has the best catalytic properties among them as evidenced by its very low activation energy, low onset potential and reproducible currents
Porphyrin aggregates in the form of nanofibers and their unusual aggregation induced emission
No full textRestricted Access.We present here the simple procedure for synthesizing elongated fibers like porphyrin aggregates. Usually whenever the aggregation in dye molecules takes place the emission always tends to quench. In this work we explore and discuss the unusual enhanced emission property of these aggregates. The nanofibers of porphyrin were characterized with the help of atomic force microscopy and UV-vis spectroscopy whereas photoluminescence spectroscopy was used to check their emission property