K-shell spectroscopy of plasmas created by intense laser irradiation of micron-scale pyramid and sphere targets

K-shell spectra of targets with microstructured features irradiated by an intense femtosecond laser have been studied. Examination of K_α emission from laser irradiated Si targets coated with micron-scale polystyrene spheres indicates that the emission is enhanced by a factor of 3 over emission from planar solids. Sphere-coated targets also emit K-shell He-like Si radiation indicating the presence of a hot dense plasma beneath the microspheres. Furthermore, K_α from Ti foils coupled to micro-tipped reentrant pyramid and wedge shaped targets has been studied, however, no significant enhancement of the K_α yield is observed for these kinds of targets. These studies illustrate that, with correct tailoring of the target surface, field enhancements can be used to increase X-ray emission from intensely irradiated targets.     

Plasma jets produced by low energy laser pulse interaction with planar and cratered targets

Laser experiments of the plasma jet formation using nanosecond laser pulses with low energy, i.e., <20 J, are presented. Planar and cratered gadolinium and aluminum targets are irradiated with laser intensities of several 10¹⁴ W/cm². Spatially-resolved time-integrated X-ray spectra were recorded in the spectral range from 7 to 10 Å. A jet-like structure is obtained from aluminum targets with a preformed crater, which is not seen in planar target irradiation. For gadolinium, a jet is observed from both planar and preformed cratered targets, suggesting that the collimation is dominated by radiative cooling. A radiation-hydrodynamics code coupled to a non-LTE ionization code was used to model the plasma. The calculated plasma emission was found to be consistent with the experimental results.     

Atomic modeling of the plasma EUV sources

We present the development of population kinetics models for tin plasmas that can be employed to design an EUV source for microlithography. The atomic kinetic code is constrained for the requirement that the model must be able to calculate spectral emissivity and opacity that can be used in radiation hydrodynamic simulations. Methods to develop compact and reliable atomic model with an appropriate set of atomic states are discussed. Specifically, after investigation of model dependencies and comparison experiment, we improve the effect of configuration interaction and the treatment of satellite lines. Using the present atomic model we discuss the temperature and density dependencies of the emissivity, as well as conditions necessary to obtain high efficiency EUV power at λ = 13.5 nm.     

Quantitative measurement of hard X-ray spectra from laser-driven fast ignition plasma

Absolute Kα line spectroscopy is proposed for studying laser–plasma interactions taking place in the Au cone-guided fast ignition targets. X-ray spectra ranging from 20 to 100 keV were quantitatively measured with a Laue spectrometer composed of a cylindrically curved crystal and a filter-absorption method for Bremsstrahlung continuum emission. The absolute sensitivities of the Laue spectrometer systems were calibrated using pre-characterized laser-produced X-ray sources and radioisotopes. The integrated reflectivity for the crystal is in good agreement with predictions by an X-ray diffraction code. The energy transfer efficiency from incident laser beams to hot electrons, as the energy transfer mechanism, is derived from this work. The absolute yield of Au and Ta Kα lines were measured in the fast ignition experimental campaign performed at Institute of Laser Engineering, Osaka University. Applying the hot electron spectrum information from electron spectrometer and scaling laws, the energy transfer efficiency from the incident LFEX, a kJ-class PW laser, to hot electrons was derived for the first time.     

Simultaneous imaging of K-α radiation and coherent transition radiation from relativistic-intensity laser-irradiated solid target plasmas

Laser acceleration of hot electrons and their transport through 12-32 μm thick Ti foils was explored experimentally using two complementary diagnostics, a bent crystal imaging the Ti K_α emission and optical imaging of the coherent transition radiation (CTR) produced by the exit of the hot electrons from the foil. The spatial extent of the hot electron production measured by these two diagnostics is dramatically different. Electrons producing CTR emerge in a spot of less than 7 μm and appear to maintain a high degree of collimation during transport through the foil while electrons that produce K_α emission appear to diverge to sizes of 50-100 μm as viewed from the back surface of the foil. These results indicate that there is a large difference in the transport of the highest energy electrons contributing to CTR signal as compared with the bulk of the hot electron population generating K_α signal.     

Measurement and simulations of hollow atom X-ray spectra of solid-density relativistic plasma created by high-contrast PW optical laser pulses

K-shell spectra of solid Al excited by petawatt picosecond laser pulses have been investigated at the Vulcan PW facility. Laser pulses of ultrahigh contrast with an energy of 160 J on the target allow studies of interactions between the laser field and solid state matter at 10²⁰ W/cm². Intense X-ray emission of KK hollow atoms (atoms without n = 1 electrons) from thin aluminum foils is observed from optical laser plasma for the first time. Specifically for 1.5 μm thin foil targets the hollow atom yield dominates the resonance line emission. It is suggested that the hollow atoms are predominantly excited by the impact of X-ray photons generated by radiation friction to fast electron currents in solid-density plasma due to Thomson scattering and bremsstrahlung in the transverse plasma fields. Numerical simulations of Al hollow atom spectra using the ATOMIC code confirm that the impact of keV photons dominates the atom ionization. Our estimates demonstrate that solid-density plasma generated by relativistic optical laser pulses provide the source of a polychromatic keV range X-ray field of 10¹⁸ W/cm² intensity, and allows the study of excited matter in the radiation-dominated regime. High-resolution X-ray spectroscopy of hollow atom radiation is found to be a powerful tool to study the properties of high-energy density plasma created by intense X-ray radiation.     

Spectroscopic observations of Fermi-degenerate aluminum compressed and heated to four times solid density and 20 eV

Shock waves generated by temporally shaped laser ablation compressed and heated Al to ρ = 11 ± 5 g/cm³ and 20 ± 2 eV. The inferred density and temperature demonstrate that highly compressed, Fermi-degenerate plasma can be created by tuning the temporal pulse shape of the laser drive intensity. The density and temperature of these plastic-tamped Al plasmas in the warm dense matter regime were diagnosed using the Stark-broadened, Al 1s–2p absorption spectral line shapes. These observations represent the forefront of opacity measurements for warm dense matter and are important for high energy density physics and inertial confinement fusion.     

石墨包覆纳米镍颗粒的结构及磁性能的表征

在密闭容器中,用爆轰分解掺杂含有镍离子的混合炸药前驱体合成了核壳结构石墨包覆镍纳米颗 粒。调整混合炸药前驱体中碳源材料和金属源材料的有效摩尔比合成了球形、不同尺寸、核壳结构的磁性石 墨包覆纳米镍颗粒。采用X 射线衍射仪(XRD)、透射电镜(TEM)、能谱分析仪(EDX)和振动样品磁强计 (VSM)表征化学构成、结构形貌及磁性能。结果表明:颗粒大小主要分布在10~55nm 之间,复合纳米颗粒 主要由面心立方镍纳米晶体和石墨碳构成,常温下这些复合纳米颗粒主要表现出超顺磁性和铁磁性能。     

Process of selective laser sintering of polymer powders: Modeling,simulation, and validation

Selective laser sintering (SLS) of polymer powders involves multiphysical transient phenomena. A numerical tool for simulating such a process is developed on the basis of the reliable modeling of the corresponding thermo-physical transient phenomena and appropriate numerical methods. The present paper addresses modeling, simulation, and validation aspects that are indispensable for studying and optimizing SLS process. The coupled multiphysical models are detailed, and the numerical tool based on the finite volume method is presented, with validations in terms of numerical and physical accuracy, by considering the shrinkage involved in the process and the successive layers deposition. A parametric analysis is finally proposed in order to test the reliability of the model in terms of representing real physical phenomena and thermal history experienced by the material during the process.