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レーザー核融合用のクライオターゲットの燃料保持容器である低密度フォームシェルの開発に成功した. ヒドロキシエチルセルロース, ポリ (p-ビニルフェノール) と塩化イソフタル酸を使用して油/水エマルションの界面縮合反応法で低密度フォームシェル表面に厚さ1～10μm, 均一性98%以上, 表面粗さ0.1μm以下の架橋高分子膜を被覆して, 気化防止層を兼ねたアブレータ付低密度フォームシェルを開発した.

Secondary nuclear reaction measurements, high speed x-ray framing camera for study of implosion dynamics and 14MeV neutron imaging technique are reviewed. Secondary nuclear reaction measurements can be used to evaluate a Fermi degenerate state in an imploded super dense plasma.

A new cross‐beam technique has been developed to measure the charge transfer cross sections of metallic atoms which have not been experimentally investigated previously. Two high‐density atomic beams were produced by the vaporization of a metal heated with an electron beam gun. A pulsed ion beam produced from one atomic beam by laser photoionization was collided with another atomic beam. By colliding the pulsed ion beam produced in this manner with the second atomic beam, the apparatus was simplified in comparison with conventional one; additionally, only a single pulsed laser shot is required to obtain the data necessary to determine a cross section. By using repetitive laser pulses it is possible to acquire in a short time a more accurate cross section as a function of impact energy. The apparatus was successfully applied to the measurement of the charge transfer cross section of gadolinium, a metallic atom with a relatively high ionization potential and high melting point.

An x‐ray emission computed tomographic technique has been demonstrated to diagnose the laser implosion uniformity of spherical targets. Three‐dimensional images of compressed core were reconstructed from five pinhole camera images obtained at different viewing directions by using an iterative algorithm. Good agreement between the experimental results and two‐dimensional hydrodynamic simulations showed that the uniformity of initial target shell thickness has a significant influence on implosion symmetry.

We have developed a monitoring system for the real-time characterization of cryogenic fuel layer in laser-fusion targets. This system is composed of an imaging interferometer, in addition to a normal target postion monitor with a single optical path. The fabrication process of a solid fuel layer in a plastic spherical shell is observed with this system. Solid fuel layer uniformity is displayed as concentric interference patterns. The distortions of the interference patterns can be interpreted as fuel layer nonuniformities.

Laser oscillations with nearly diffraction limited output beam of a copper vapor laser (CVL) were investigated. The beam divergence less than 0.3 mrad in the pulse duration of 75ns was attained by the long pulse excitation. Also, good beam quality in the whole pulse duration was obtained by the injection locking, with the threshold injection power of only 0.1 W. The CVL beam quality has been successfully established for the master oscillator power amplifier.

This case report describes isolated aneurysm of the left internal iliac artery with neurofibroma. A 72-year-old man was seen at the hospital because of a left inguinal mass, and was found to have a strangulated hernia and an isolated aneurysm of the left internal iliac artery. The patient was admitted to the hospital for treatment. At operation, the inguinal tumor so strongly adhered to the surrounding tissue that we were obliged to select resection of the ilioinguinal nerve, testicular artery, and vein in order to remove the tumor. Intraoperative frozen section diagnosis of the tumor was neurofibroma, and so the tumor was left intact. Then the left internal iliac artery was freed, its central side was ligated to its peripheral side, and the aneurysm was removed. This case of isolated internal iliac aneurysm coexisted with neurofibroma is relatively rare. The anatomical location of the aneurysm make the early detection difficult, and it is often found after rupture has occurred. We could resect the aneurysm before rupture. This patient has been in good condition for postoperative 12 months.

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.

The present paper summarized recent activity of the target fabrication group at Institute of Laser Engineering (ILE), Osaka University. We focused on (1) organic photovoltaic materials to suppress the damage from laser-shine-through and (2) new emulsion technique to fabricate polyimide capsule. The following topics describes briefly, (3) organic feromagnetic materials for magnetic levitation of the target, (4) ultralow density foams of hydrocarbon whose density is ~2.0 mg/cc with micrometer-sized structures, and (5) new ultrathin (~nm) adhesion technique to provide laser-shock experiment targets.

Hydrodynamic instability in laser-irradiated targets have been investigated in detail by using ultra high-speed x-ray radiographic technique. Recently developed high-resolution x-ray imaging for laser-driven Rayleigh-Taylor (RT) instability experiments as well as data including RT growth rate, ablation density and plasma density profile are desribed. Results are of great importance for comprehensive understanding of the dispersion relation of the laser-driven RT instability. Especially, direct observation of the ablation density was first achieved with temporal and spatial resolutions of 100 ps and 3 μm, respectively. Imaging techniques includes x-ray Moire imaging, x-ray penumbral imaging and Fresnel phase zone plate imaging coupled with x-ray streak cameras or x-ray CCD cameras. Experiments were performed by using Gekko-XII/HIPER laser system at the Institute of Laser Engineering, Osaka University.

We present recent results on the hydrodynamic instability experiments on the HIPER (High Intensity Plasma Experimental Research) laser facility at Institute of Laser Engineering, Osaka University. We measured the Rayleigh‐Taylor growth rate on the HIPER laser. Also measured were all parameters that determine the RT growth rate. We focused on the measurements of the ablation density of laser‐irradiated targets, which had not been experimentally measured. The experimental results were compared with calculations with one dimensional simulation coupled with and without Fokker‐Planck equation for electron heat transport.

The bulk laser damage threshold of lithium triborate (LiB3O5) single crystals were determined to be 45.0 GW/cm2 at 1.064 μm, 1.1 ns pulse width. The damage threshold was dependent on pulse duration and wavelength: at 1.064 μm, 25 ns the damage threshold was 11.2 GW/cm2, at 0.532 μm, 1.0 ns the damage threshold was 26 GW/cm2; and at 0.355 μm, 0.9 ns the damage threshold was 21.9 GW/cm2. To the best of our knowledge this is the highest value reported among inorganic frequency conversion crystals, and approximately 1.8 times higher than that of fused silica.

A scheme to suppress the Rayleigh-Taylor instability has been investigated for a direct-drive inertial fusion target. In a high-Z doped-plastic target, two ablation surfaces are formed separately-one driven by thermal radiation and the other driven by electron conduction. The growth of the Rayleigh-Taylor instability is significantly suppressed on the radiation-driven ablation surface inside the target due to the large ablation velocity and long density scale length. A significant reduction of the growth rate was observed in simulations and experiments using a brominated plastic target. A new direct-drive pellet was designed using this scheme.

Two kinds of source developments were tried for the generation of pulsed medium-mass ion beams. The first was the pure anode plasma formation with the fs-laser light irradiation of a (conductive) graphite target. The other was beam production from a dielectric anode, which was covered with a diamond like carbon film or silicon layer. The preliminary results were disclosed here.

To demonstrate the feasibility of the fast ignitor scheme,1,2 a 100 TW Petawatt Module laser (PWM) was illuminated onto an uniformly imploded spherical shell target. The neutron yield is enhanced from below 105 up to 106 for the first time and agree with those estimated from the simultaneously detected high energy deuteron yield and spectrum. A few hundred keV deuterons collide with the cold deuterons in core. Without PWM, no neutrons are observed above the detection threshold of 105.

Intense proton and nitrogen beams were focused on various sample materials to observe the surface ablation thickness. The thickness change and the surface composition change with the beam dose were measured with various analysis methods.

A 25 J −1.053 μm pulse in 0.45 ps (a0= 2.2) was injected into a gas jet. This excited a large amplitude self‐modulated wakefield. By increasing the pulse length from 0.45 to to 1.2 ps, the wakefield grew close to the wave‐breaking limit, which sustained a 350 ± 150 GV/m acceleration field over a 1 mm dephasing distance along the laser axis in a plasma with density 2 × 1019 cm−3. This resulted in electrons accelerated to 300 MeV. The amplitude saturation of the wakefield is explained by a pump depletion effect to the large amplitude forward Raman instability. The Petawatt Laser is completed, which will be used to accelerate electrons above one GeV.

To demonstrate the feasibility of the fast ignitor scheme, the 100 TW Petawatt Module laser PWM was illuminated on an imploded spherical CD shell, which enhanced neutron yield ~106 for the first time. This is due to the fusion reactions between the energetic deuteron beam and cold dense deuterons. Without PWM, we have observed no neutrons above the detection threshold ~105. Proton rear emission and possible gigagauss scale magnetic fields from 60 TW laser illuminated plastic target are observed in a good agreement with a two-dimensional PIC simulation. The PWM is up graded to the world biggest Petawatt Laser (say PW laser). The out put is 1 Petawatt, which is used also for ultra-intense laser matter interactions above the intensity of 1020 W/cm2.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An imploded plasma core is irradiated by a 100 ps laser pulse in a model experiments of fast ignition. Additional laser pulses for drilling and heating are introduced co- axially with the laser beams for the implosion. The preformed imploded core is created by the 12 beams of 0.53 micrometers laser with the total energy of 800 J. The additional heating pluses contain 100 ps pulses separated by 300 ps at the wavelength of 1.06 micrometers with the total energy of 320J. The first pulse is intended for drilling the coronal pulses surrounding the core and the second is for addition heating of the core. We measured the imploded core additionally heated with 100 ps pulses.

Ultra-fast x-ray imaging is of great importance for diagnosing laser-driven inertial confinement fusion (ICF) plasmas. Typical required spatial and temporal resolutions are 10 micrometer and 10 ps, respectively. We have developed variety of one- (1D) and two-dimensional (2D) image sampling technique for ultrafast time-resolved x-ray imaging with x-ray streak cameras. Moire imaging of an x-ray-backlit target has been developed as 1D image sampling of an objective with 1D repetitive structure with a spatial resolution of 5 micrometer for use in experiments on hydrodynamic instabilities in laser- accelerated targets. With 1D sampling of repetitive 2D images, a multi-imaging x-ray streak camera (MIXS) with temporal- and spatial-resolutions of 10 ps and 15 micrometer, respectively, has been developed and successfully utilized for diagnosing uniformity and heating process of the imploded core plasmas. Two types of spectroscopic applications of the MIXS have been developed. One is multi-channel MIXS (McMIXS) which has three MIXS channels with various spectral responses for time- resolved 2D temperature measurement. Another is monochromatic MIXS (M-MIXS) for temperature, density and material mixing measurement, in which monochromatic images with Bragg crystals are coupled to MIXS. Finally, 2D image sampling of a 2D image on an x-ray streak camera (2D-SIXS) was also developed.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We prepared optical thin films grown with surface chemical reactions using TiCl 4 and H 2 O for TiO 2 . The nonuniformity of thickness distribution was under 1% over 240 mm in diameter. The structure of TiO 2 film grown at 25 degrees Celsius was amorphous. The structure changed into polycrystalline with an increase of growth temperature up to 400 degrees Celsius. Secondary ion mass spectrometry showed that chloride residents presented in the films at every growth temperature. However, these chloride residents could be removed by thermal annealing at 400 degrees Celsius. The TiO 2 film at the growth temperature of 25 degrees Celsius had a laser-induced damage threshold of 5 J/cm 2 for 1-ns, 1064 nm laser pulse. The damage threshold of TiO 2 films decreased at higher growth temperature. Chloride in the films had no influence on the laser-induced damage threshold.

An optical phase conjugation and laser pulse compression of laser light via stimulated Brillouin scattering at high energy are investigated. SBS operation at high-energy and high average power in fluorocarbon liquids is clarified. Fundamental nonlinear and SBS optics data on particle-free Fluorinert liquids are presented. High capacity SBS cells filed with particle-free Fluorinert liquids were used to demonstrate a very high energy SBS mirror in recent experiments at GEKKO XII laser facility. The pulses of energy as high as 73 Joules were phase conjugated using a SBS phase conjugating mirror. High energy SBS laser pulse compressor was operated at the level 30 Joules. Laser pulse with duration 13 ns FWHM was compressed to 0.6 ns with a high SBS internal efficiency.

This paper will discuss the laser conditions for producing efficient thrust on debris. In order to obtain high thrust for given laser energies, thermal energies dissipated into laser ablation and debris bulk have to be minimized. It was suggested that this minimization can be achieved by using ultrashort pulse interactions where laser pulse duration is too short for thermal conduction to take place deep into debris. The results of momentum coupling coefficients measured with ps and ns pulse duration will be presented.

This paper describes the widows for laser transport in the atmosphere. The limitations caused mainly by Rayleigh scattering, stimulated Raman scattering, thermal blooming and so on are discussed here. From these limitations, windows for laser space applications are found out. The widows have enough area in laser parameters for several applications of laser in the space.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have newly developed a two dimensionally (2D) space-resolved spectrometer for an ultra high intense laser plasma experiment. Output of this data, we can obtain four dimensional informations: space(2D), spectrum, and intensity. An optical fiber bundle is combined with a Cross Czerny-Turner type spectrometer to acquire 2D space-resolved spectrum. This has the spectral resolution 0.8 nm and the space 8 μm. Back-scattered light was measured from plasmas irradiated with an ultra-intense laser pulse at laser intensity 10 19 W/cm 2 . The obtained spectra show distinctive difference depending on both spatial and intensity profiles.

In the direct-drive scheme implosion of the inertial confinement fusion, the hot spark formation is critically affected by laser irradiation non-uniformities and subsequent hydrodynamic instabilities. Influence of the low- modal irradiation non-uniformities on the hot spark formation was investigated by means of the time- and space- resolved x-ray spectroscopic measurements. Experimental results were compared with post-processed hydro-code simulations by the aid of x-ray spectrum analysis code.

In order to study the ion acceleration in ultra-intense laser plasma interactions, we measured neutron spectra from the D-D ion nuclear reactions in the target. 50-100TW/0.5-1 ps laser light irradiated obliquely dueterated plastic solid targets with different laser polarizations and intensities. Comparing the neutron spectra with the 3D Monte-Carlo simulation indicates ion acceleration in the near target normal direction at any polarization and increases in the ion energy with laser intensity.

IN order to directly observe low-mode implosion nonuniformities, especially of l equals 1, which prevents stable formation of a hot spark in the compressed core plasma at the final stage of the implosion, a series of direct-drive implosion experiments has been performed at the Gekko-XII glass laser facility by using gas-filled plastic- shell targets. Partially coherent light (PCL) was used as a drive laser to suppress middle- to higher-modes of the irradiation nonuniformity down to approximately 1 percent. A clear shift from the center of the chamber and a slight crosswise structure were seen in the time- and space- resolved shape of the shell in the accelerating phase with an x-ray framing camera and absorbed laser intensity were also estimated by using a rocket equation. In order to confirm the property of these results, separate experiments under similar laser conditions were performed by using Au- coated sapphire spheres as surrogate target. The x-ray intensity distribution on the circumference of the target in the XFCs image, which is strongly dependent on the drive nonuniformity in the accelerating shell resulted from the l equals 1 drive nonuniformity. In our experiments, the l equals 1 drive nonuniformity due to some reproducible factors was found to be of the order of approximately 10-20 percent.

Generation of a long laser-plasma channel capable of triggering and guiding an electrical discharge is a crucial issue for laser-triggering protection system. We make a long plasma channel to increase the probability of triggered lightning by laser. To produce a long laser plasma channel, we propose da new technique called hybrid plasma channel method which combines weakly and strongly ionized plasma channels to maximize laser-energy efficiency of discharge guiding. We investigate the characteristics of the hybrid plasma channels to maximize laser-energy efficiency of discharge guiding. We investigate the characteristics of the hybrid plasma channel method through several laboratory experiments. The weakly ionized channel was generated by UV laser pulses in air. As the number density of electrons in weakly ionized channel is proportional to 1.1 power of laser intensity, nitrogen and oxygen molecules can not attributed to the source of ionized plasma. It is suggested that dissociation process of impurities in air whose density is 1011 - 1012 cm-3 plays an important role in plasma formation and leader triggering effect. The 50 percent flashover voltage using the hybrid plasma channel method is lower than that without the weakly ionized plasma channel. It was also found that higher repetition rate of the plasma generation on lowers the V50 furthermore.

Reviewed are the progress in direct drive implosion researches with Gekko XII laser system. Precise observation of the growth rate of Rayleigh-Taylor instability and the suppression of imprints using indirect-direct hybrid implosion have been investigated. Theoretical and experimental researchers on the fast ignition scheme are also studied. Relativistic laser plasma interaction experiments with Peta-Watt Module and Gekko XII are also described. Finally, the future direction of the research including the development of solid state laser for fusion reactor is discussed.

We prepared optical thin films grown with surface chemical reactions using TiCl 4 and H 2 O for TiO 2 , Al(CH 3 )3 and H 2 O 2 for Al 2 O 3 as reactants. The uniformity of thickness distribution was good over 240 mm in diameter. The film thickness could be preciously controlled only by the number of cycles. Two-layer TiO 2 /Al 2 O 3 anti-reflection coating with less than 0.2 percent reflection loss at 532nm was fabricated. Laser induced threshold strongly depend on the growth temperature and the introduced gas pressure. They increasing with decreasing the growth temperature and with increasing the introduced gas pressure.

Laboratory and field experiments for laser triggered lightning were performed in order to induce so called triggered lightning, in which an electric leader initiates from tall objects on the ground to thunderclouds, using a plasma channel produced by CO2 lasers and Nd lasers. Significant milestone was achieved in technological developments and verification of a scientific feasibility of the techniques such as determination of laser trigger timing which lead to laser triggered natural lightning. In the laboratory experiments technologies to produced long plasma channels and characteristics of discharge process induced by plasma channels were extensively investigated. In the field experiments developed are an automatic laser trigger system using an RF burst emission by a preliminary breakdown, methods to measure lightning path, thundercloud movement and field strength, and to make a continuous plasma channel at the top of the lightning tower which acts effectively for leader initiation.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The progress of implosion physics research and relevant technologies enable us to examine technical and economical feasibility, and to plan the realistic strategy to the commercial power plant. The most important key issue for IFE is the driver technology. The development of the laser fusion driver is opening new industrial technologies based on the photon processes and new fields of high energy physics.

A series of field experiments for laser triggered lightning have been carried out targeting the winter thunderstorms in Fukui, Japan. A combination of a 2 kJ CO 2 laser system, a 600 J Nd-glass laser and a 4th harmonics 100 mJ YAG laser was used to produce a plasma channel which are effective to trigger and guide an electrical leader from the lightning tower. A new scheme of autotriggering laser system by preliminary breakdown (PB) has been developed. The PB triggering system demonstrated its capability of irradiating the laser at the right timing for triggering the leader. On February 11th 1997, in the field experiment, the electric leader was initiated by the laser plasma using the PB triggering system for the first time. A number of diagnostics including UHF interferometers, a tower current monitor, a capacitive antennas verified the initiation of leader triggered by the laser plasma both in time and space.

A novel laser architecture of laser-diode pumped eight pass 1064-nm Nd:YAG zig-zag slab laser amplifier was developed aiming to achieve high energy extraction efficiency and good beam quality. A high energy extraction efficiency of up to 73% for the laser mode volume has been achieved in this amplifier operating at an initial small signal gain of 3.36. The excellent beam quality factor M2 of 1.2 has been obtained. The compensation of thermal birefringence in this amplifier was successfully performed.

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.

We report the high-sensitivity measurements of 2D thermal birefringence distribution in LD pumped Nd:glass (HAP4) laser under lasing at 1054 nm and non lasing conditions. The thermal birefringence was reduced under the lasing condition compared to the non lasing condition. By inserting a 90 degree(s) quartz rotator between two identically LD pumped Nd:glass rods, almost perfect birefringence compensation was achieved with very little residual birefringence. A considerable reduction of birefringence loss from over 20% before compensation to less than 1% after compensation was observed.

The design and construction of an efficient near-infrared holosteric optical parametric oscillator amplifier based on KTiOPO4 (KTP) crystal are reported. The system is tunable from 840 to 1451 nm and generates up to 0.45 mJ at 920 nm with 27% efficiency in 4 - 6 ns pulses. The 532 nm pump source is a frequency doubled laser-diode pumped Nd:YAG laser producing up to 2 mJ in 8 ns, 50 Hz pulses. We have used the system to study the fluorescence lifetimes of Yb:YAG and Yb:glass as a function of wavelength. The data reveal interesting variations in the reabsorption enhanced Yb-ion lifetime. Some Yb:YAG samples exhibiting a sharp increase in their lifetime near the peak absorption wavelengths. The longest lifetime measured in a few mm thick sample of Yb:YAG was 3.3 ms, which would be highly beneficial for energy storage applications using laser diodes.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An efficient laser‐diode (LD) array surface pumped Nd:YAG disk amplifier with an optical‐optical conversion efficiency of 12% was demonstrated. A double‐pass output energy of 67 mJ (input energy, 10 mJ) in a 1 ns pulse at 50 Hz rate was obtained. The two‐dimensional thermal stress‐induced birefringence in the disk amplifier was successfully measured using a newly designed polarimeter. An energy extraction efficiency of 65% was obtained which was well fitted to the Frantz‐Nodvik equations taking into account of the thermal birefringent loss.

A series of laboratory experiments has been conducted to investigate the initiating effects of laser plasma channel on electrical discharge. It was confirmed that the plasma channels reduce the required electrical field strength for electrical discharges to occur by a factor of 6. A field experimental site targeting natural lightning is being prepared. The thunderstorm monitoring system and the laser and optical systems have been developed and tested against various weather conditions. The results from the laboratory experiments and field experiments will be discussed.