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Direct-drive implosion experiments on the GEKKO XII laser (9 kJ, 0.5 μm, 2 ns) with deuterium and tritium (DT) exchanged plastic hollow shell targets demonstrated fuel areal densities (ρR) of ˜0.1 g/cm2 and fuel densities of ˜600 times liquid density at fuel temperatures of ˜0.3 keV. (The density and ρR values refer only to DT and do not include carbons in the plastic targets.) These values are to be compared with thermonuclear ignition conditions, i.e., fuel densities of 500–1000 times liquid density, fuel areal densities greater than 0.3 g/cm2, and fuel temperatures greater than 5 keV. The irradiation nonuniformity in these experiments was significantly reduced to a level of ρR was directly measured with the neutron activation of Si, which was originally compounded in the plastic targets. The fuel densities were estimated from the ρR values using the mass conservation relation, where the ablated mass was separately measured using the time-dependent X-ray emission from multilayer targets. Although the observed densities were in agreement with one-dimensional calculation results with convergence ratios of 25–30, the observed neutron yields were significantly lower than those of the calculations. This suggests the implosion uniformity is not sufficient to create a hot spark in which most neutrons should be generated.

円筒状の炭素繊維強化プラスチック（Carbon Fiber Reinforced Plastic：CFRP）をロールシェルとして使用したロールは“カーボンロール”と呼ばれ，鉄，アルミと並ぶ第三のロールとして定着してきた。近年の製紙機械は紙幅10m程度にまで広幅化しており，運転速度は2,000m/minのレベルになっている。広幅で高速という条件は，装置内のロールにとっては正に過酷な条件であり，それを克服するためにカーボンロールが採用されている。しかし，ただ単にカーボンロールを使えばよいと言うわけにはいかない。高速安定運転を実現するためには，適正な設計に基づいて，かつその設計を高度に具現化する製造技術により製造されたカーボンロールが必須となる。 本稿ではカーボンロールの原料として最適な超高弾性率ピッチ系炭素繊維を用いた高速・広幅製紙機械向けロールの設計の考え方を説明し，次に我々が提案する動フレの抑制技術について具体的な測定データを交えて紹介する。これらを踏まえて面長10mL，抄速2,000m/minの製紙機械向けのロールの設計を行ってみたところ，鉄ロールと比較して，（１） ロール径は1/2，（２） 重量は1/6，（３） 慣性モーメントは1/25に低下させることが出来る事が分かった。当該ロールを採用することにより，著しい小径化・軽量化・低慣性モーメント化が達成され，製紙機械のコンパクト化，省エネ，そして何よりも安定したロール回転による安定操業に貢献することができる。

The diode-pumped slab laser for inertial fusion energy driver has been demonstrated, which produces the 1053-nm output energy of 10 J at 10 Hz. The glass slab laser amplifier has been pumped by quasi-CW 290-kW AlGaAs laser-diode arrays at 803 nm. The optical system can compensate for thermal effects by use of zigzag optical propagation, image-relayed telescope, and 45° Faraday rotator. The output energy of 10.6 J at 1 Hz with the optical-to-optical conversion efficiency of 19.9% has been successfully obtained. Also, the 10-Hz operation has been performed with an output energy of 5.1 J. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(2): 27–35, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20288

We have developed a highly sensitive two-dimensional (2D) polarimeter that can sensitively measure the direction of the principal birefringence axis as well as the phase shift δ with its sign when δ

Experimental results of the thermal and spectral characteristics of a monolithic stack of high power quasicontinuous wave 940-nm InGaAs linear laser diode arrays have been evaluated. Thermal resistance as the most important thermal parameter characterizing a high-power laser diode package was obtained using the temperature rise measured directly by a thermo-camera. A new simple and convenient technique to measure a spectral transition of the emission from laser diode arrays is proposed. Spectral chirping due to the transient thermal power dissipated during the laser pulse was observed as a time-evolution of the spectral profile; it gave a comprehensible image of the chirping behavior. Comparing the temperature rise in the diode junction with the thermal simulation, it was determined that the thermal shift of central wavelength dλ/dT was 0.21 nm/°C. Detailed performances were identified for pumping a Yb3+ doped crystalline laser, and it was verified that the laser diode arrays were satisfactory to meet pumping source requirements for coupling to Yb3+ absorption linewidth.

We have proposed and designed a laser-diode-pumped laser driver for inertial fusion energy (IFE) which consists of water-cooled zig-zag path Nd: glass (HAP-4) slab amplifiers. A driver module was designed under the several operational constraints and has 10 kJ total output energy at 351 nm and operates at 12 Hz with 9-12% overall efficiency. The laser driver producing 4 MJ blue output for IFE will consist of 400 modules

The fast ignitor scheme for achieving inertial fusion energy precompresses the DT fuel to more than 1000 times the solid state density with nanosecond laser pulses. It then employs a picosecond 10–100-PW laser pulse to deposit with very high efficiency the energy necessary to achieve the ignition temperature of approx. 4 keV. In this way the necessary driver energy for inertial fusion energy reactors is reduced from the megajoule level to the 100-kJ level. In this article, we present results relevant to the development of the fast ignitor scheme that have been achieved in recent years by Australian teams in collaboration with international teams. The topics that are specifically addressed are: (1) forces and relativistic mechanisms of laser interaction with the electrons in the intense picosecond beams; (2) electron and ion emission from the focused beam into the precompressed plasma, including double layer effects and collective stopping power; and (3) the energy of the picosecond beam, which when nearly uniformly deposited into the precompressed DT-fuel can achieve the conditions for high-gain volume ignition. Positive results are derived for the volume ignition scheme from considerations of recent high neutron gain laser fusion experiments.

We have proposed and designed a laser-diode-pumped laser driver for inertial fusion energy (IFE) which consists of water-cooled zig-zag path Nd:glass slab amplifiers. A driver module was designed under the several operational constraints and has 10 kJ total output energy at 351 nm and operates at 12 Hz with 10.4% overall efficiency. The laser driver producing 4 MJ blue output for IFE will consist of 400 modules.

A three dimensional (3D) analysis code of thermal birefringence in solid-state lasers was developed. Basic equations include thermal conduction, absorption of laser energy, thermal stress and thermal birefringence. Relative phase shifts induced by thermal effects measured and obtained by simulation are in good agreement with quantitatively. Edge effects of thermal birefringence are quantitatively estimated by 3D simulation. Those are unable to be estimated by 2D analysis.

The recent high core gains of 29% in laser fusion experiments at the LLE Rochester are evaluated and compared with related earlier measurements where surprisingly the self-similarity model for volume compression provides a common description. This is a proof that the isentropic conditions of stagnation-free compression were mostly fulfilled at the optimized experimental gains, in contrast to highly entropy-producing shock and central spark conditions. Some projections are given of how these results may be generalized to volume ignition for the parameters of the NIF (National Ignition Facility). The proof of stagnation-free volume compression for the best laser fusion gains indicates the advantages of volume ignition, which not only is ‘robust’ and simply follows the natural adiabatic compression, but also is much less sensitive to instabilities and mixing. However, its essential advantage is that it is free from symmetry problems – in contrast to spark ignition, with its spherical detonation front.

A focusing optical system for a semiconductor laser-diode-array is described. The high-power array consists of a number of minuscule light sources (quantum wells) as well as a stratified structure, so that it requires several design techniques to focus as a pumping source for a laser-diode-pumped solid state laser. Some design techniques for such a focusing system are proposed with examples of the design of an anamorphic optical system.

An X-ray emission computed tomography technique has been demonstrated to diagnose the laser implosion uniformity of spherical targets. Three-dimensional images of the compressed core were reconstructed from five pinhole camera images obtained at different viewing directions by using an iterative algorithm. The uniformity of the heated plasma is estimated from the intensity distribution of the X-ray emitted from the surface of the target.

Plant growth experiments by using visible semiconductor diodes, that is, light emitting diode (LED) and laser diode (LD) are reviewed. It is well known that the spectra needed for green plants growth are red and blue. The central wavelengths of emission spectrum of LED used are 660nm and 450nm. The oscillation wavelength of LD used is 670nm. We grew a plant (sprouting radish) for the first time by using a red LD and two blue LEDs as a light source for photosynthesis. In particular experimental methods and results under pulsed illuminations are described in detail.

The present status of the measurement of thermal birefringence and its compensation in laser-diode (LD) pumped Nd:glass laser rods is reviewed. To measure the two-dimensional (2D) thermal birefringence in solid-state laser materials such as Nd:glass (HAP4) a high-sensitivity polarimeter is introduced.This polarimeter can sensitively measure the direction of the principal birefringence axis as well as the phase shift δ with sign when δ < π/4. The 2D thermal birefringence and its compensation in a LD pumped Nd:glass (HAP4) rods are successfully measured with this polarimeter. The birefringence compensation is reported by inserting a 90° rotator between two identical LD pumped Nd:glass rods with conduction cooling. The birefringence loss due to this thermal birefringence in a polarized laser cavity can be estimated by using Jones matrix. A considerable reduction of birefringence loss from 9.8% to less than 0.9% after compensation is performed.

Growth experiments of Sprouting Radish were carried out for the first time by using a red laser diode (LD) and two blue light emitting diodes (LED) as the light source for the photosynthesis. The output power and the central wavelength of the LD are 5 mW and 670 nm, and those of the LED are 1.2 mW and 450 nm, respectively. The type of the LD is selected so that the central wavelength of the LD matches to the band center of the absorption spectrum of the plant. It is found that the plant under the artificial light grows similarly to that under sunlight.

レーザー技術開発の最新の進展により,レーザー核融合において新しい研究の展開がある。(1)CPA(チャープパルス増幅)法によりペタワットレーザーの建設が可能となり,超高密度プラズマの瞬間的加熱による「高速点火」の研究が開始された。(2)核融合炉用レーザーとしてDPSSL(ダイオード励起固体レーザー)の技術開発に期待が集まっている。(3)米国等で点火へ向けて次段階の研究が開始されようとしており,NIF(国家点火実験施設)の建設が決定されている。上記3点についてその現状を紹介する。

We measured the wavelength shift and wavelength chirping of a high- power quasi-cw twodimensional (2D) laser diode (LD) array by using the polychromator we constructed. The absorption efficiency calculated was compared with experimental values of a Nd: YAG amplification module pumped by using a quasi-cw 2D LD array. We propose that the optimum 2D LD array pumping systems should use a feedback control either on the time-resolved spectrum of LD or on the transmitted power during pulsed operation.

To prove the principle of a solar laser, a laser diode was directly operated by a current from a solar cell. Average laser power of 2.5 mW (5 mW standard) per a laser diode was obtained at a voltage of 2.2 V, however, the power was decreased by a cloud which shut out the sunlight. As the operation current of the laser diode is limited to 70 mA, it is necessary for avoiding the damage of the laser diode to choose a proper laod resistance of the circuit. It was found that the value of resistance 2Ω was suitable for the present system.

For achieving tunable and single longitudinal mode oscillation, a Fox-Smith type mode selector with a Fabry-Perot etalon was incorporated in a TEA CO2 laser. The etalon was inserted in the optical path taken out from the main cavity of the CO2 laser for protecting the etalon from damage on the surface. According to the longitudinal mode resulting from the etalon and the Fox-Smith optical path, the single mode oscillation of purities of more than 99% and 95% was performed with the probabilities of 55% and 100%, respectively. The tunability of a laser frequency was obtained with the purity of more than 75% over the whole gain region of the TEA CO2 laser by controlling the tilting angle of the etalon or the optical path length of the Fox-Smith system.

Possibility of completely-controlled plant factory using laser as light source for photosynthesis is discussed in detail. It is shown that visible laser diodes (LD) together, according to circumstances, with second-harmonic generation (SHG) technique of total efficiency nearly 30% can compete with commonly used high-pressure sodium lamp. This level may be attainable both technically and economically in some future.

The present status of laser-diode (LD) pumped high-power Nd: YAG lasers at 1.06μm is reviewed. With a side-pumped rod geometry, an output of of 1.25J per pulse is demonstrated. The LD-end-pumped Nd: YAG laser can produce an output power of CW 60W in a near-diffraction-limited beam. A one Joule per Q-switched pulse LD-pumped Nd: YAG zigzag-slab laser is constructed. A 1-kW average-power LD array-pumped folded zigzag-slab Nd: YAG laser is demonstrated at 2.25 kHz. A phase conjugated LD-pumped Nd: YAG MOPA laser architecture is proposed to have a 1 kW average power in a near-diffraction-limited beam. An LD pumped Nd: YAG regenerative amplifier is achieved simultaneously with a high gain (71dB) and a high energy extraction efficiency (48%) .

A novel polarimeter for measuring the two-dimensional (2D) thermal- and mechanical-stress-induced birefringence in solid-state laser materials such as Nd:YAG is proposed. Using this device, we could sensitively measure the direction of the principal birefringence axis as well as the phase shift δ with sign when δ < π/4. The 2D thermal- and mechanical-stress-induced birefringence in a laser-diode-pumped Nd:YAG rod was successfully measured with the proposed polarimeter. We also found an active quarter-wave Nd:YAG phase retarder.

High density compression of main fuel and stable formation of hot spark at the center of imploded core have been investigated to obtain the scaling and the requirements for fusion ignition and high gain. For this purpose, the experimental data of the high density compression up to 600 times solid density with hollow shell pellet have been analyzed and compared with simulations.

For a laser diode (LD) pumped solid-state laser system using high power LD arrays, compact optical sensors of high speed, high response, low noise and low cost are needed. We constructed optical probes using Ge avalanche photo-diode (APD) and Si-APD for the wavelength region of 0.3-1.6μm. To measure the intensity distribution of laser beams, spectral distribution, and wavelength shift of LD arrays, we used a CCD linear image sensor and a polychromator which were designed and constructed.

Using Jones matrix formulation, the theoretical calculations of birefringence compensation technique for a quarter-wave plate scheme are presented. This scheme was proposed and experimentally demonstrated by W. A. Clarkson et al. (Opt. Lett. 24 (1999) 820). In the present paper we have theoretically confirmed that using this method, even in principle, complete compensation is not possible. However, it is shown quantitatively that this scheme does makes possible effective compensation for the birefringence in as few as several tens of watts of pumping power region, which is an attractive feature for laser-diode (LD) pumped solid-state laser systems. We also found good agreement between our theoretical calculations and experimental results obtained by W. A. Clarkson et al. For example, from the analysis we show that only < 0.1% loss will be generated by about 10 W of heat deposited in the rod. This corresponds to about 30 W of LD pump power, which may generate from 6 to 10 W output power depending upon the conversion efficiency of type lasers

A high-power argon excimer laser has been developed with an output power exceeding 2 MW in the VUV region at 126 nm. As an alternative to a conventional Al/MgF(2)-coated mirror, which was susceptible to damage, an uncoated quartz plate was successfully used as a reflector for reproducible high-power operation of the argon excimer laser without any mirror damage. Observation of the temporal behavior of the laser pulse in relation to that of the gain coefficient is discussed.

A gated neutron streak camera with a uranium oxide cathode has been developed for laser fusion experiments. The energy spectrum of secondary electrons was improved by coating the uranium oxide cathode with thin cesium iodine. The tube design was carried out by computer calculation of electron trajectories. The newly developed streak tube showed a temporal resolution of about 70 ps. This streak camera can be applicable to a neutron yield greater than 1012 with a reasonable signal‐to‐noise ratio by gating a microchannel plate electron multiplier.

A series of laser fusion implosion experiments of plastic hollow shell targets was performed by using the Gekko XII glass laser in order to achieve the required fuel areal density for ignition. Introducing random phase plates to improve illumination uniformity, high-density compression of more than 600 times deuterium liquid density has been achieved. The implosion dynamics and symmetry were observed with a spatially resolved x-ray streak camera and an x-ray multiframing camera. The three-dimensional emission profile of the laser-heated plasma was reconstructed from the x-ray images by use of computed tomography and was compared with the laser illumination profiles. The areal density of the imploded core was measured by the neutron activation of a silicon tracer, the secondary reaction method, and the knock-on proton method. Although the measured density and areal density were consistent with those from 1-D hydrodynamic simulation, experimental neutron yields were significantly lower than those predicted by the simulation for convergence ratios larger than 20. This suggests that better implosion uniformity is required to create a hot spark.

We report several experimental results on debris collection for radiochemistry in inertial confinement fusion research. The collection efficiency was measured by means of radioactive tracers 24 Na, 82 Br, 152m1 Eu and activatable tracer 151 Eu in glass or plastic shells. It is shown that the collection efficiency depends on the atomic weight of the tracer and the surface condition of the collector, and does not greatly depend on the initial areal density of the target, in our experimental conditions.

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.

Planer stripe and foil targets coated with NaF were irradiated with high intensity 351 nm laser radiation of 130 ps duration. Time-integrated as well as time-resolved measurement of gain on NaXIHα at 54.2A were made. A time-integrated gain of 1.2−1.1+0.8cm−1 and a time-resolved peak gain of 3.2±1.0 cm−1 were obtained. A detailed account of the experimental procedures for determination of gain is given.

Looking into the worldwide laser device sales by application and the commerciallaser devicesales by laser types, we forecast a nearly 200% annual growth rate for laser-unitsales and dollarvolume by market of the leser diode (LD) pumped solid-state lasers. A futurcorrelation betweenLD laser diode or LD pumped solid lasers and other lasers in thenear-infrared, visibleand ultra-violet regions foresees that dye lasers and gas lasers will be replacedby LD and/or LDpumped solid-state lasers.

Having a larger stimulated emission cross section and stronger fluorescence emission, a laserdiode (LD) pumped Nd: YVO4 laser has higher efficiency and power than Nd: YAG laser.Spectral property and CW end-pumped lasing characteristics have been measured on thismaterial. Stimulated emission cross section of 2.5×10-18cm2 for π polarization, slope efficiencyof 48.6% and light to light conversion efficiency of upto 40% for laser rod along a-axiswere obtained.

Detailed computation and experimental results of thermal birefringence loss in TGG and glass based Faraday rotator rod was presented. These data will be useful for designing a laser system and a thermally compensated Faraday rotator.