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To create a conceptual design of a tracking system of a target injected into a wet-walled, laser-fusion reactor, the influence of residual gas on the target trajectory is discussed based on a kinetic model, assuming all of the impinging molecules are adsorbed on the target surface. The model targets are a high-gain target for central ignition and a fast-ignition target with a cone as an optical guide for an additional heating laser. In the case of a fast-ignition target, tracking in the reactor might be skipped, depending on its condition, because of the heavy cone. Recent activities in fabrication of the fast-ignition target are briefly mentioned. more...

AbstractThis paper describes a possibility to control of laser ablation using material functionality. As an example, a remarkable difference is shown in the laser ablation of a polystyrene film coated with a photovoltaic perylene/phthalocyanine bilayer when compared with a bare polystyrene film after irradiation at an intensity range of 109∼ 1010W/cm2(λ=1064 nm, 1.1-ns FWHM). Without the bilayer coating, the laser pulse formed spiky structures in the polystyrene film as self-focusing traces of the laser pulse, while for the coated film, the uniform surface ablation trace without the spiky interior structures was observed. The phenomena in the presence of the organic photovoltaic coating material agree with the required ablation to achieve high-density compression of the fuel capsule for inertial fusion energy. more...

Millimeter‐sized highly spherical poly(amic acid) (PAA) capsules were prepared by curing an emulsion containing non‐volatile N,N‐dimethylacetamide (DMAc). Although the sphericity of the capsules (>99%) obtained by the emulsion method was slightly lower than that of corresponding polystyrene capsules, their surface was smooth. The curing conditions to achieve the highest degree of sphericity require stabilization and deformation, which were governed by parameters, such as PAA concentration, the viscosity of the emulsion matrix, stirring speed, and temperature. more...

Effects of an implosion nonuniformity with ℓ = 1 (ℓ: Legendre polynomial mode number) on the hot spark formation were investigated in a series of direct-drive implosion experiments at the Gekko-Xll glass laser (Yamanaka et al., 1987). The implosion dynamics and the performance from the early to final stage of the implosion were observed with a variety of X-ray imaging and neutron diagnostics. A drive nonuniformity in the implosion with ℓ = 1 was observed in the shape of the accelerated target at the early stage of the implosion. At the final stage of the implosion, the resultant nonuniformity with ℓ = 1 was also observed as a geometrical shift of core plasmas from the center of the chamber. The observed neutron yield and X-ray emission properties at the final stage of the implosion were significantly degraded with an increase of the implosion nonuniformity with ℓ = 1. The experimental results were compared with one-dimensional (1-D) and two-dimensional (2-D) hydrodynamic simulations. As a result, it was found that the implosion nonuniformity with ℓ = 1 shifts the whole implosion dynamics towards its direction and prevents the confinement of the gas fuel considerably. However, the experimentally observed degradation in the hot spark formation, such as reductions in neutron yield and features in X-ray emission, can be reproduced in 2-D simulations not with an asymmetric perturbation of ℓ = 1 only but with multimode nonuniformities such as ℓ = 1 coupled with some additional middle-mode ones (e.g., ℓ = 6). Such a complex spike structure caused by the multimode nonuniformities was found to be essential for the experimentally observed rapid cooling of the hot spark. more...

An electrodialysis method has been adopted to the solution growth of 5 cm×5 cm single crystals of KDP. The c-axis growth rate of 3 mm/day was obtained by using Cr3+ion as dopant. The assessment of the grown crystal has been done by means of an etching method to make a comparison with the crystals grown by the temperature falling method. more...

Stokes pulses of high energy and high-average power were obtained by stimulated Brillouin scattering (SBS) compression of long Nd:YAG laser pulses. The SBS medium used in the single-cell compressor was liquid ultrafiltered Fluorinert FC-75 fluorocarbon. An output pulse duration of 0.9 ns and a peak-power enhancement by 1 order of magnitude were observed for 10-ns, 0.57-J input pulses at a 10-Hz repetition rate. The compressor internal SBS efficiency reached a value of η_SBS = 94% and the overall device efficiency a value of η_dev = 87%; both values are the highest reported so far to the best of our knowledge. The simple single-cell SBS geometry provided excellent energy and pointing stability of the Stokes pulse. Its temporal shape turned out to be somewhat less stable. The SBS process also partially improved the laser beam quality. The Stokes pulses proved to be capable of generating radiation in the extreme-ultraviolet and soft-x-ray regions over a period of two months without any significant output deterioration. more...

A high-purity molybdenum (Mo) mirror was developed by an electron-beam melting method (e.b.m. Mo mirror). For the high-power TEA CO_2 laser, the e.b.m. Mo mirror has two to four times higher surface damage threshold than that of an Au-coated glass mirror and three times longer lifetime than that of a powder metallurgy Mo mirror (p.m. Mo mirror) when laser energy density lower than 60 J/cm^2 was irradiated with a 0.5-pps repetition rate. It was found that the difference between the e.b.m. Mo mirror and the p.m. Mo mirror at the laser-damage threshold was due to the fine surface without voids and the small amount of impurities. more...

Coordination structures of neodymium(III) complexes with some ß-diketones were investigated in terms of their correlations with emission efficiency in deuterated dimethylsulfoxide (DMSO-d6). The analysis of UV-vis spectra, 13C NMR, electrospray mass spectrometry (ES-MS) spectra, XANES and EXAFS analysis of tris(hexafluoroacetylacetonato)neodymium(III) complex, [Nd(hfa-H)3(H2O)2], and tris[bis(perfluorooctanoyl)methanato]neodymium(III), [Nd(pom-H)3], in DMSO indicated that the deuterated tris(hexafluoroacetylacetonato)neodymium(III), Nd(hfa-D)3, and deuterated tris[bis(perfluorooctanoyl)methanato]neodymium(III), Nd(pom-D)3, in DMSO-d6should have a symmetrical, rigid and bulky shell composed of six inner-coordinating DMSO molecules and three weakly coordinating hfa-D and pom-D molecules. The improvement in the emission efficiency of the neodymium complexes with the low vibrational and weakly coordinating ß-diketonates in DMSO-d6was ascribed to their symmetrical rigid coordination structures, which should suppress radiationless transition via vibrational excitation and energy migration in the fluid system. more...

Heavy fluorocarbon liquids were found to be an ideal medium for high-power stimulated Brillouin scattering experiments. Fluorinert FC-75 gives high reflectivity, near 98%, and excellent fidelity in phase conjugation of 14-J, 18-ns optical pulses. The complete removal of microparticle impurities was found to be essential for avoiding laser damage in a high-energy operation. A method of purification based on ultrafiltration has been developed. more...

We measured the two-dimensional birefringence compensation in laser-diode (LD) pumped Nd:glass (HAP4) laser rods with a high-sensitivity polarimeter. The compensation was performed by inserting a 90° quartz rotator between two identical LD pumped Nd:glass rods with conductive cooling. A considerable reduction of birefringence loss from 9.8% to less than 0.9% after compensation was observed. more...

The photoluminescent property of a bilayer of phthalocyanine and a perylene derivative, a part of an organic photovoltaic cell, was investigated. The monolayer of the perylene derivative exhibited photoluminescence at 824 nm with lifetimes of 1.6 ns and 0.10 ns. The steady state and time-resolved photoluminescence of the 100-nm perylene derivative layer were efficiently quenched with a 100-nm phthalocyanine coating. The high efficiency of the quenching was explained by the high mobility of the photogenerated carrier in the n-type semiconducting perylene derivative, and agreed with the insensitivity of the photovoltaic property of the bilayer to the thickness. more...

Photosensitized luminescence of Nd3+in solution was successfully observed for the first time by coordinating the metal cation with deuterated 4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-pentadecafluoro-1-pentafluorophenyl-1,3-decanedione as a ligand with a low vibrational chromophore. more...

The effect of an overcoat layer on highly reflective coatings used for high-average-power lasers is presented. For high-average-power lasers, it is important to diffuse temperature localized due to such factors as impurity absorption in the coating. It was predicted from the calculation of thermal diffusion that the temperature rise was considerably relaxed in the radial direction by use of an overcoat layer which had high thermal conductivity. The damage threshold at a pulse repetition rate of 30 Hz was increased to about 20 J/cm2from about 12 J/cm2by adding an Al2O3overcoat layer to a highly reflective coating. more...

The deuterium-tritium (D-T) thermonuclear reaction region of a laser-driven large-high-aspect-ratio target, which contains D-T mixture gas, has been diagnosed with an ?-particle imaging technique using a pinhole camera. The residual pusher region at the maximum compression has also been observed as an image of scattered ?-particles. Comparison between the ?-particle image and a two-dimensional hydrodynamic simulation shows that laser energy balance significantly influences the implosion uniformity. more...

We report the high-sensitivity measurements of two-dimensional (2D) thermal birefringence distribution in a laser-diode (LD) pumped Nd:glass (HAP4) laser under lasing (at 1054 nm) and under no lasing conditions. The thermal birefringence was reduced under the lasing condition owing to the depletion of stored energy by stimulated emission. By inserting a 90° quartz rotator between two identical LD pumped Nd:glass rods, almost perfect birefringence compensation was achieved. The power loss due to thermal birefringence was evaluated quantitatively using the Jones matrix method. A considerable reduction of power loss, from over 12% before compensation to less than 0.4% after compensation, was observed. The output performance of this laser was in fairly good agreement with the estimation after taking into account the power loss due to thermal birefringence. more...

The temperature dependence of the emission cross-section of Yb (5 ×1020atoms/cm3)-doped fluorophosphate glass has been investigated in the temperature range from 77 K to 380 K. The emission cross-section has been evaluated from the measured fluorescence spectra and the lifetime, using the Füchtbauer-Ladenburg formula. A large change in the emission cross-section from about 0.6×10-20cm2at 380 K to 1.1×10-20cm2at 77 K was obtained by decreasing the temperature. The effect of reabsorption is found to be significant even at temperatures as low as 160 K which leads to underestimation of the emission cross-section values. more...

This paper describes measurements of the ablation pressure for 10.6 µm and 1.05 µm laser irradiation using thin-foil acceleration observed by X-ray backlighting and X-ray streak shadow graphs of the implosion of a spherical target. At an absorbed laser intensity of 1014W/cm2, the ablation pressure was more than 10 Mbar for laser wavelengths of 10.6 µm and 1.05 µm. The results are compared with theories based on the self-regulated flow model and the flux-limited thermal conduction model. more...

We investigated the anomalous laser light transmission phenomenon by means of optical backlighting and sideward shadowgraphy as well as the calorimeteric and spectroscopic measurements of transmitted light. These experimental data and relevant numerical simulation suggest that the evaporation of the target material by the amplified spontaneous emission of the laser system is one of the feasible factors in this effect. more...

A Wolter type-I X-ray mirror designed for laser plasma diagnostics has been fabricated by the replication method. A master mandrel has been ground by a diamond grinder and polished by a computer-controlled machine. The replicated mirror coated with gold can be used for X-rays longer than 2.5 Å. X-ray imaging tests were performed with a laboratory X-ray source. more...

Page : 1657Wrong (Received September 29, 1978) Corrected (Received September 29, 1977)

A method of selecting hollow glass microballoons for laser fusion research is described. The average wall thickness and uniformity are measured by an Interphako interference microscope illuminated with white light. A convenient method for measuring the quantity of the loaded fuel is discussed. more...

This paper reports a nuclear analysis of the neutrons from a DT pellet measured in inertial confinement fusion experiments in the GEKKO XII glass laser system. The items discussed are the neutron energy spectrum from a pellet and the outside of the chamber wall, the neutron leakage fraction through the wall and the windows of the chamber, the induced radioactivity of the activation test pieces, and the effects of these on the neutron measurements. The dose due to the fusion neutrons and ?-rays and the induced radioactivity is also described. more...

A new target is proposed which increases both the laser absorption rate and the hydrodynamic efficiency. This target consists of a light inner shell and a massive outer shell with pinholes for entry of the laser light. The acceleration mechanism is similar to that of a cannonball. A model for this acceleration is presented and compared with hydrodynamic simulations. more...

The laser parameters such as an inversion density, a stimulated transition cross section and a loss factor in the glass laser amplifier medium were experimentally determined. Using these values, the rate equations of Baser amplifier were solved with various input pulse forms. To get extremely high output power, it is necessary to send a very steep input pulse into an amplifier. An experiment of two-stage amplifier was performed and the maximum output power obtained was 1.1 GW, which well agreed with calculations. The various problems in amplification were considered. To get larger power, the mode locked laser was prepared. The SeOCl2-Nd3+liquid laser seems to be more durable against a damage of laser rod. An experiment of laser amplifier consisting of glass and SeOCl2lasers was performed. The sufficient gain could be obtained even if the center spectrum of the SeOCl2laser was about 50 Å shorter than that of the glass Baser. more...