Tatsuhiko Yamanaka

Strategies for enhancing photoluminescence of Nd3+ in liquid media

Abstract The excited state (4F3 2) of Nd3+ readily undergoes radiationless energy transfer via vibrational excitation of surrounding medium and dipole-dipole energy transfer via cross relaxation and energy migration, which makes it difficult to observe luminescence of Nd3+ in a liquid matrix. In order to suppress such de-excitation of the 4F3 2 state, two kinds of s-diketonato ligands which have no CH and OH bonds having high vibrational frequency were successfully designed for observing luminescence of Nd3+ in a liquid matrix. Luminescence of Nd3+ was observed for the first time by using deuterated tris-(hexafluoroacetylacetonato) neodymium(III), Nd(HFA-D)3, in deuterated organic solvents. The luminescence intensity, lifetime and quantum yield of the complex were measured in methanol-d4, acetone-d6, THF-d8, DMF-d7 and DMSO-d6. Deuterated tris(bis-(perfluorooactanoyl)methanol)neodymium(III), Nd(POM-D)3, gave enhanced luminescence in DMSO-d6 by minimizing energy migration during diffusional collisions in the liquid matrix. The intensity was independent of concentration in the micromolar range from 0.01 to 0.07M. The bulky perfluoroalkyl groups in the ligands effectively prevented de-excitation via vibrational excitation and cross relaxation in liquid media.

Scalings of implosion experiments for high neutron yield

A series of experiments focused on high neutron yield has been performed with the Gekko‐XII green laser system [Nucl. Fusion 27, 19 (1987)]. Deuterium–tritium (DT) neutron yield of 1013 and pellet gain of 0.2% have been achieved. Based on the experimental data from more than 70 irradiations, the scaling laws of the neutron yield and the related physical quantities have been studied. Comparison of the experimental neutron yield with that obtained by using a one‐dimensional fluid code has led to the conclusion that most of the neutrons produced in the stagnation phase of the computation are not observed in the experiment because of fuel–pusher mixing, possibly induced by the Rayleigh–Taylor instability. The coupling efficiency and ablation pressure have been calculated using the ion temperature measured experimentally. A coupling efficiency of 5.5% and an ablation pressure of 50 Mbar have been obtained.

Observation of proton rear emission and possible gigagauss scale magnetic fields from ultra-intense laser illuminated plastic target

CR-39 film stacks are used to measure the energy and angular distribution of protons emitted from the rear surface of ultra-intense laser illuminated plastic foils. The experiment suggests that the energetic protons are dragged away from the rear surface, where the hot electron formed a virtual cathode. The two-dimensional particle in cell simulation supports this hypothesis. For 5 (100) μm thick target, 1.8×109 protons have a slope temperature of 3 (2) MeV. The ring structure of proton emission leads us to the hypothesis that a toroidal magnetic field associated with the hot electrons works on the fast ions and deflects them. From the logarithmic slope of the ring diameter versus the ion energy, the product of the magnetic field × the length over which it works on the ions is estimated to be up to 1000 MG⋅μm. The simulation shows that a strong toroidal magnetic field was excited at the target rear side with expansion of plasmas. The proton’s angular distribution from the rear surface has the logarithmic ...

Enhancement of luminescence of Nd3+ complexes with deuterated hexafluoroacetylacetonato ligands in organic solvent

Abstract Tris-(hexafluoroacetylacetonato)neodymium(III), [Nd(HFA-D)3], was prepared by chelation of Nd3+ ion with deuterated hexafluoroacetylacetone in CD3OD. Luminescence of the Nd3+ complex was observed for the first time in organic solvents and the quantum yield was estimated to be of the order of 10−2 in deuterated acetone solution. The absorption spectrum of [Nd(HFA-D)3] dissolved in acetone was comparable with that of Nd3+ ion in Y3Al5O15 matrix (Nd:YAG). Splitting of the 4 F 3 2 level was determined to be 82.3 cm−1 in this system. These spectral characteristics suggest that the physical nature of Nd3+ coordination environments should be uniform and well defined by coordination of HFA in solution.

Nuclear fusion: Fast heating scalable to laser fusion ignition

Rapid heating of a compressed fusion fuel by a short-duration laser pulse is a promising route to generating energy by nuclear fusion, and has been demonstrated on an experimental scale using a novel fast-ignitor geometry. Here we describe a refinement of this system in which a much more powerful, pulsed petawatt (1015 watts) laser creates a fast-heated core plasma that is scalable to full-scale ignition, significantly increasing the number of fusion events while still maintaining high heating efficiency at these substantially higher laser energies. Our findings bring us a step closer to realizing the production of relatively inexpensive, full-scale fast-ignition laser facilities.

Studies of ultra-intense laser plasma interactions for fast ignition

Laser plasma interactions in a relativistic parameter regime have been intensively investigated for studying the possibility of fast ignition in inertial confinement fusion (ICF). Using ultra-intense laser systems and particle-in-cell (PIC) simulation codes, relativistic laser light self-focusing, super hot electrons, ions, and neutron production, are studied. The experiments are performed with ultra-intense laser with 50 J energy, 0.5–1 ps pulse at 1053 nm laser wavelength at a laser intensity of 1019 W/cm2. Most of the laser shots are studied under preformed plasma conditions with a 100 μm plasma scale length condition. In the study of laser pulse behavior in the preformed plasmas, a special mode has been observed which penetrated the preformed plasma all the way very close to the original planar target surface. On these shots, super hot electrons have been observed with its energy peak exceeding 1 MeV. The energy transport of the hot electrons has been studied with making use of Kα emissions from a see...

Optical thin films consisting of nanoscale laminated layers

The control of the refractive index of laminated coatings consisting of alternating stacks of nanoscale Al2O3 and TiO2 sublayers grown by atomic layer deposition has been achieved. The refractive index of the coating linearly changed from 1.870 to 2.318 as the thickness of the single TiO2 sublayer was varied from 2.0 to 39 A while that of the single Al2O3 sublayer was kept constant at 5.5 A. The refractive index could be varied by adjusting only the number of growth cycles of each material. This approach will have potential applications to optical multilayer coatings consisting of well-controlled extremely thin layers.

Formation of A = 12. sigma. /sup -/ hypernucleus from K/sup -/ absorption at rest; Observation of a. sigma. /sup -/ spin-orbit doublet of narrow widths

High-resolution spectroscopy of ..pi../sup +/ from K/sup -/ absorption at rest has been used for the first time to identify ..sigma../sup -/ hypernuclear states. The observed spectrum from a (CH)/sub n/ target has revealed a p/sub 3/2/-p/sub 1/2/ doublet of /sup 12/Be with narrow widths. The spin-orbit splitting of ..sigma../sup -/ is deduced to be 5 MeV, 0.8 times that for nucleons.

Progress of fast ignitor studies and Petawatt laser construction at Osaka University

100 TW light from the Petawatt Module (PWM) laser illuminated a preimploded spherical deuterated polystyrene(CD) shell target. The DD neutron yield increased from 2.5×105–106. Analysis indicates that hundreds of keV deuterons, generated around the critical density, collide with cold fuel deuterons and play the leading role in the enhancement of the neutron yield. A two-dimensional particle-in-cell (2D PIC) simulation predicted well the deuteron spectrum. A 60 TW laser was used for MeV proton emissions and megagauss magnetic fields generation on the rear surface of a Poly p-xylene(C8H8) plane target. The 2D PIC simulation explained well the results. The PWM laser was upgraded to one PW, making it the world biggest Petawatt laser (PW laser). An optically parametric chirped amplification was introduced in the front end. The pulse was synchronized to the GEKKO XII imploding beams to within 10 ps.

Basic and integrated studies for fast ignition

Basic and integrated studies are conducted on fast ignition (FI) using various large laser systems. A Peta watt (PW) laser system is used to study the basic elements relevant to FI and can also be injected to a compressed core to test the FI integrated experiment when coupled with a GEKKO twelve laser beam system. Using a spherical target inserted with a Au cone guide for the PW laser pulse, an imploded core is heated up to 1 keV resulting in neutron increase 1000 times more than that without heating pulse. Details of the implosion are examined at the Omega laser system of this type target with indirect implosion scheme and are compared with simulation results. LASNEX simulation indicates that a 400 g/c.c. high density core could be achieved with this scheme at 1.8 MJ laser input.