Turbulence in fluids is a ubiquitous, fascinating, and complex natural phenomenon that is not yet fully understood. Unraveling turbulence in high density, high temperature plasmas is an even bigger challenge because of the importance of electromagnetic forces and the typically violent environments. Fascinating and novel behavior of hot dense matter has so far been only indirectly inferred because of the enormous difficulties of making observations on such matter. Here, we present direct evidence of turbulence in giant magnetic fields created in an overdense, hot plasma by relativistic intensity (10 18 W∕cm 2 ) femtosecond laser pulses. We have obtained magneto-optic polarigrams at femtosecond time intervals, simultaneously with micrometer spatial resolution. The spatial profiles of the magnetic field show randomness and their k spectra exhibit a power law along with certain well defined peaks at scales shorter than skin depth. Detailed two-dimensional particle-in-cell simulations delineate the underlying interaction between forward currents of relativistic energy "hot" electrons created by the laser pulse and "cold" return currents of thermal electrons induced in the target. Our results are not only fundamentally interesting but should also arouse interest on the role of magnetic turbulence induced resistivity in the context of fast ignition of laser fusion, and the possibility of experimentally simulating such structures with respect to the sun and other stellar environments.intense laser matter interaction | high energy density | astrophysical simulations | filamentary structures T he largest terrestrially available magnetic fields are generated when an intense laser pulse (intensity above 10 18 W∕cm 2 ) irradiates a solid target (1-3). The high energy density produced by laser irradiation generates relativistic electron jets, through the process of wave breaking. These relativistic electron jets carry the laser energy deep into the target ionizing and heating the colder portions behind the laser generated plasma and exciting return shielding currents. In the laboratory, such heating is extremely important for fast ignition of highly compressed targets in laser fusion (4, 5), simulation of intra planetary matter existing at ultrahigh pressure (6), ultrafast X-ray pulses (7), as well as proton and ion acceleration up to the MeV-GeV levels (3). It also serves as an excellent tool for modeling astrophysical systems (8-10). The transport of relativistic electrons through hot dense matter is very complex and is barely understood (11,12). Simulations have shown that relativistic electron transport in plasma media is fraught with severe plasma instabilities particularly the Weibel instability (13), which leads to spatial separation of forward and backward currents and eventually to the emergence of turbulent structures (14) and rapid energy dissipation. A major physical parameter that mirrors this complex physics is the giant magnetic field-as high as hundreds of megagauss-generated in this interaction. In earlier st...

Generation and application of energetic, broadband terahertz pulses (bandwidth ~0.1–50 THz) is an active and contemporary area of research. The main thrust is toward the development of efficient sources with minimum complexities—a true table-top setup. In this work, we demonstrate the generation of terahertz radiation via ultrashort pulse induced filamentation in liquids—a counterintuitive observation due to their large absorption coefficient in the terahertz regime. The generated terahertz energy is more than an order of magnitude higher than that obtained from the two-color filamentation of air (the most standard table-top technique). Such high terahertz energies would generate electric fields of the order of MV cm-1, which opens the doors for various nonlinear terahertz spectroscopic applications. The counterintuitive phenomenon has been explained via the solution of nonlinear pulse propagation equation in the liquid medium.

Room temperature ferromagnetic ordering is observed in chemically grown ZnO nanocrystals. Nanocrystals are simultaneously capped by two different organic molecules inducing p-type and n-type defects. A saturation magnetization of 0.008 emu/g is achieved at 300 K. Incorporation of Mn 2+ ions at substitutional sites in nanocrystals gives rise higher saturation magnetic moment at lower doping level. ZnO nanocrystals codoped with Mn 2+ and Co 2+ and prepared under identical conditions revealed an increase in saturation magnetization. However, the saturation magnetic moment remains lower than that obtained for Co 2+ -doped ZnO nanocrystals prepared by the same method. An increase in saturation magnetization was invariably associated with quenching of photoluminescence emission. These findings reaffirm that magnetism in nanocrystals is a defect induced phenomenon that can be controlled by choice of capping agent as well as incorporation of the transition metal impurity. Magnetization as a function of temperature [M(T)] curve is discussed in view of available reports on the global exchange mechanism in these ferromagnetic nanocrystals.

ZnSe and ZnSe∕ZnS core/shell quantum dots (QDs) of two different sizes (4.5 and 3.5nm) have been synthesized. The nonlinear absorption is measured at 1064nm using a 35ps laser with an open aperture Z-scan setup. Three-photon absorption (3PA) has been observed in ZnSe and ZnSe∕ZnS QDs. 3PA cross section is found to be about four orders of magnitude larger than bulk ZnSe, and three orders of magnitude higher than ZnS QDs. 3PA cross section is found to be increased in ZnSe and in ZnSe∕ZnS QDs with decreasing size from 4.5to3.5nm, due to strong confinement effect.