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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.

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.

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.

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.

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.

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.

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.

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.

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.

Copyright 1990 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments, 61(10), 2763-2785, 1990 and may be found at http://dx.doi.org/10.1063/1.1141830

レーザ核融合のみならず精密工学を含む先端科学技術分野に大きな波及効果を及ぼすことが期待されている新しいパワーレーザとして, (i) LD励起固体レーザ, (ii) X線レーザ, と (iii) 自由電子レーザとをとりあげ, 概説することにする.

右側脳室上衣下出血にて発症し, 脳血管写にて両側頚動脈, 椎骨動脈系にはその起始部から異常は認められなかったが, 右中大脳動脈M1部にのみ閉塞像とその周囲でのモヤモヤ様血管網を認めた1例について追跡しえたので報告する.本症例は発症後1年を経過しているが, 閉塞部位及びモヤモヤ様血管網の進展をみておらず, モヤモヤ病類似疾患, 更には最近報告されている特発性中大脳動脈閉塞症ともその病態が近似していると考えられたため, これらの疾患との関係について考察を加えた.

A portable optically pumped far-infrared (FIR) waveguide laser having a modified Chang-type output coupling is constructed and its characteristics are studied by using a CH2F2lasant. The new output coupling is designed so that lasing wavelength from 10 μ m to a few millimeters can be observed. Reproducible and stable FIR laser output is observed, although the tuning curve is very complex due to the low-loss multimode oscillation.

A high power 12.08μm NH3 laser optically pumped by a TEA CO2Iaser was developed for UF6laser isotope separation. A rectangular metai waveguide was used to confine efficiently the energy of the pumping CO2 laser. The output energy of 50 mJ (500kW) with the energy conversion efficiency of about 2% was obtained. The NH3pressure dependence of the output energy and the characteristics of the polarization of the laser light were studied, and lasing mechanism was discussed from laser pulse shapes.A 16μm CF4 laser with the similar waveguide system was also developed. The output energy of 5mJ was obtained.

Woltor type 1 X-ray optics for laser fusion diagnostics has been developed. Its purpose is to image the soft X-ray emission for the laser target interaction region over a field of view of hundreds of μm with high sensitivity and micro resolution. It was fabricated by ultra precision grinding, super polishing and vacuum replication. These fabrication processes are described in this paper. The developed optics were tested in the laboratory with X-rays (C Kα ; λ= 44.8A, Al Kα ; λ=8.3 A, Ti Kα ; λ=2.7 A). The results of that evaluation show that the developed optics has spatial resolution of several μm in a field of view of 1.2 mm. But, in the region of short wavelength (λ=2.7 A), spatial resolution of this optics was worse. This paper also describes X-ray imaging test of laser plasma.

In order to excite some molecules besides 11SCl3vibrationally, a line selective CO2 laser has been constructed. Maximum cw output at each band through a main mirror, of 91.5 reflection is 16, 12, 7and 6.5W/line for 9.2, 9.6, 10.2 and 10.6μm band, respectively, and the total number of generated lines is 84. No spectral change is observed in the selective excitations of 11BCl3, 10BCl3 and 32SF6 in Xe matrix at 47 K. However, by temperature rise under successive irradiation, the peak height of crystalline 11BCl3 increases remarkably at 76-80K, and reaches the maximum value at 100 K. It is found that the pulsed irradiation is effective for the selective excitation of 11BCl3 or 10BCl3. In the case of 32SF6 excitation, pre-irradiadiation with a cw CO2 laser at 47 K promotes the crystallization of 32SF6 by a temperature rise of the sample. This implies the fact. that vibrationally excited 32SF6 molecules have been gathered to form the crystal readily.

An optically-pumped 385-μm D2O laser system has been constructed for the Thomson scattering ion temperature measurement in a Tokamak plasma. Stable single transverse and stable tunable (over ±1 GHz) operation is performed on the pump TEA 9R (22) CO2 laser using a Zn Se etalon temperature-controlled within ±0.01°C. The frequency of the 385-μm D2Olaser can be tuned to the N2O absorption line center at 778. 192 GHz.At 385-μm, maximum output power of 120 kW, and a quantum efficiency as high as 21% are obtained. The saturation broadening with D2O absorption line is for the first time observed using the ±1 GHz tunable 9R (22) CO2 laser. And, pressure broadening coefficient of N2O absorptionline is measured using the ±1 GHz tunable 385-μm D2O Raman laser to be 7.6 MHz/torr.