TJCID—21417 Contents DE88 011752 Preface ii Neodymium-Glass Laser Research and Development al LLNL 1 Nova Laser Technology 8 Building Nova: Industry Relations and Technology Transfer IS Managing the Nova Laser Project 26 Optical Coatings by the Sol-Gel Process 34 Frequency Conversion of the Nova Laser 42 Eliminating Platinum Inclusions in Laser Glass ' 52 Detecting Microscopic Inclusions in Optical Glass 64 Auxiliary Target Chamber for Nova 68 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi­ bility for Ihe accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer­ ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise dc«s not necessarily constitute or imply its endorsement, recom­ mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. tAfci Preface ince the early 1970s, Lawrence construction of the Nova laser Livermore National Laboratory facility. These four articles first S has played a prominent role in appeared in the February 1983 issue the national effort to achieve ot Energy ant! Technology Review controlled nuclear fusion by the (LLNL report UCRL-52000-85-2). inertial-confinement method. The article "Optical Coatings by Working with a series of ever the Sol-Gel Process," from the more powerful lasers, researchers in October 1985 E&TR {LLNL report the LLNL Laser Program have UCRL-520D0-85-10), describes our greatly increased their understanding chemical process for making the of basic laser physics and have damage-resistant, antvreflective silica steadily advanced the limits of laser coatings used on the Nova laser power. Nova, the newest laser glass. The technical challenges in facility at LLNL and the most designing and fabricating the KDP powerful in the world, was dedicated crystal arrays used to convert the in early 1985. light wave frequency of the Nova The articles reprinted here laser are reported in "Frequency record several milestones in laser Conversion of the Nova Laser." Two research at LLNL. "Neodymium- articles. "Eliminating Platinum Glass Laser Research and Inclusions in Laser Glass" and Development at LLNL" recounts the "Detecting Microscopic Inclusions in history of the Laser Program and our Optical Glass," describe how we work on neodymium-glass lasers. dealt with the problem of damaging "Nova Laser Technology" describes metal inclusions in the Nova laser the capabilities of the Nova laser glass. The last article reprinted here, and some of its uses. "Building "Auxiliary Target Chamber for Nova: I-.dustry Relations and Nova," discusses the diversion of Technology Transfer" illustrates the two of Nova's ten beamlines into a Laboratory's commitment to work secondary chamber for the purpose with U.S. industry in technology of increasing our capacity for development. "Managing the Nova experimentation These articles Laser Project" details the appeared in the April-May 1986 organization and close monitoring of E&TR (LLNI. report 52000-86-4/5). costs and schedules during the Howard Lowdermilk Associate Program Leader Neodymium-Glass Laser Research and Development at LLNL During the past decade, we have designed and constructed a series of increasingly energetic and powerful neodymium-glass solid- state lasers for research in weapon physics and in inertial confinement fusion (ICF). The twofold focus of our continuing efforts in laser research and development is on (1) the design and fabrication methods that will significantly reduce the cost of a 10-MJ, 500-TW laser system, and (2) the development of techniques for operating solid-state lasers at high average power and efficiency. For more than a decade, LLNL has to highlight some of the key For further information contact been centrally involved in the nation's accomplishments of the development VV. F. Krupke (4151 J22-53S4. inertial-confinement fusion (ICF) campaign. program. The principal goals of the ICF program are to produce, in the rigin of the ICF Program laboratory, high-gain implosions of the In inertial confinement fusion, fusion fuel, to apply ICF technology and O high-power laser beams rapidly facilities to nuclear-weapon physics heat the surface of a target capsule, research and to military applications, usually containing a deuterium-tritium and, ultimately, to generate cost-effective, fuel mixture, to form a plasma envelope. central-station electric power. In direct The rocket-like blowoff of plasma support of this program, we have material from the surface drives the developed the technology base and capsule inward to compress and heat the increased the energy and peak power fuel. When the core reaches a density of levels of neodymium-glass lasers by 10' to 104 times that of liquid water and several orders of magnitude. On the a temperature of 10K degrees (10 keV), occasion of the initial operation of the the fuel ignites. Thermonuclear bum most recent of these laser systems. Nova, spreads rapidly throughout the it is appropridle to review the strategic compressed and inertially confined fuel, technical issues of inertial fusion that we yielding many times the driver input addressed in the early 1970s, to outline energy. Shortly after the invention of the the considerations that led to the ruby laser in 1960, computer calculations selection and subsequent development were made at LLNL to simulate the of neodymium-glass systems for ICF irradiation of tiny deuterium-tritium and weapon-physics research, and (D-T) pellets by .ritense pulses of laser light and their subsequent implosion to U.S. inertial fusion effort. At that time, thermonuclear conditions. A! this same both laboratories were engaged in time, it was recognized th.ll the fusion exploratory development of several types microexplosions could eventually he of lasers for possible use in inertial applied to the generation of power. confinement fusion, including carbon Calculations revealed, however, that dioxide, neodymium-glass. hydrogen efficient generation of fusion energy fluoride, and atomic iodine lasers. would not result from simple laser Because it was judged that all of these heating of the thermonuclear fuel. lasers could, with sufficient development, Instead, to generate fusion energy, lasers be scaled to the required energy and would have to compress and implode peak power levels, selection of which the fuel to 10000 times its liquid density. types to pursue was centered on the Experimental work to create hot operating wavelengths of the lasers and plasmas using lasers began in the mid- on their potential for high average power 1960s al several laboratories including and efficiency. LLNL Neutron generation from planar Analyses of plasma physics, coupled lithium-deuteride targets was reported with LLNL computer calculations, by Soviet researchers in 1968. With this indicated that i( would be highly demonstration of neutron generation beneficial to deliver the bulk of the from laser-heated plasmas, interest energy to the target at shorter intensified in seeking an answer to the wavelengths'; at a short enough basic question Can we design fusion wavelength, the laser radiation incident pellets that will produce useful on the fusion pellet would be absorbed thermonuclear gain {that is, release primarily through inverse during thermonuclear fusion more than bremsstrahlung, and a thermal plasma 100 times the energy used to implode would be created. These computations the fusion fuel) when driven by also enabled us to identify and technologically and economically characterize a number of undesirable practical lasers? competing energy-absorption processes The best available computer-based that, at longer wavelengths, would lead estimates for laser-driver requirements to nonthermal plasmas and to deleterious with gains of 100 were many orders of preheating of the fusion fuel. Analyses magnitude beyond the energy and peak of the activation thresholds for these power levels of lasers available in the detrimental absorption mechanisms earlv 1970s. Thus, it became evident that indicated that their thresholds would be the minimum drive requirements could higher when shorter-wavelength laser (and should) be determined using light was used. experimentally flexible, single-shot laser Although we could not. at that time, systems, and that development of the project quantitatively the laser intensity efficient, repetitively pulsed laser systems at which these unwanted processes needed for the more demanding fusion would occur, it was clear that by applications could (and should) be selecting a laser driver with the shortest undertaken separately and at a rate operating wavelength, the physics risk in consistent with growing knowledge of driving efficient dense implosions would the minimum drive requirements. be significantly reduced. Thus, on the basis of wavelength considerations alone, the neodymium-glass laser became the election of Lasers for ICF laser of choice because it has the shortest In 1971 and 1972, tlv U.S. Atomic operating wavelength of 1.05pm SEnergy Commission and its (compared to 10.6