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Pulsed Power for Solid-State Lasers

Beginning in the early 1970s, a number of research and development efforts were undertaken at U.S. National Laboratories with a goal of developing high power lasers whose characteristics were suitable for investigating the feasibility of laser-driven fusion. A number of different laser systems were developed and tested at ever larger scale in pursuit of the optimum driver for laser fusion experiments. Each of these systems had associated with it a unique pulsed power option. A considerable amount of original and innovative engineering was carried out in support of these options. Ultimately, the Solid-state Laser approach was selected as the optimum driver for the application. Following this, the Laser Program at the Lawrence Livermore National Laboratory and the University of Rochester undertook aggressive efforts directed at developing the technology. In particular, at Lawrence Livermore National Laboratory, a series of laser systems beginning with the Cyclops laser and culminating in the present with the National Ignition Facility were developed and tested. As a result, a large amount of design information for solid-state laser pulsed power systems has been documented. Some of it is in the form of published papers, but most of it is buried in internal memoranda, engineering reports and LLNL annual reports. One of the goals of this book is to gather this information into a single useable format, such that it is easily accessed and understood by other engineers and physicists for use with future designs. It can also serve as a primer, which when seriously studied, makes the subsequent reading of original work and follow-up references considerably easier. While this book deals only with the solid-state laser pulsed power systems, in the bibliography we have included a representative cross section of papers and references from much of the very fine work carried out at other institutions in support of different laser approaches. Finally, in recent years, there has been a renewed interest in high-average-power solid-state glass lasers. Much of the prime power technology developed in support of this has definite applications in the long term for fusion power plant scenarios

The effect of temporal pulse shape on optical damage

The conditions under which optical materials are susceptible to laser-induced damage is a topic which has been the subject of considerable study. Laser parameters such as wavelength and temporal pulse duration have been studied extensively. Until this work the effect of temporal pulse shape has not been considered. We present here data from a simple single-parameter model and a supporting experiment which predicts that a Flat-In-Time-pulse will produce damage at approximately 80% of the fluence of a Gaussian pulse of the same FWHM duration

Size-selection initiation model extended to include shape and random factors

The Feit-Rubenchik size-selection damage model has been extended in a number of ways. More realistic thermal deposition profiles have been added. Non-spherical shapes (rods and plates) have been considered, with allowance for their orientation dependence. Random variations have been taken into account. An explicit form for the change of absorptivity with precursor size has been added. A simulation tool called GIDGET has been built to allow adjustment of the many possible parameters in order to fit experimental data of initiation density as a function of fluence and pulse duration. The result is a set of constraints on the possible properties of initiation precursors

Energy storage and power conditioning system for the Shiva laser

An optimal energy delivery system for the world's largest glass laser system has been designed based on computer modeling and operation of laser hardware. Components of the system have been tested on operating lasers at LLL. The Shiva system is now under construction and will be completed in 1977. The energy supply described here will provide cost-effective, reliable power and facilitate the gathering of data in pursuit of controlled thermonuclear reactions. (auth

A Summary of Recent Damage-Initiation Experiments on KDP Crystals

ABSTRACT We summarize recent investigations of the density and morphology of bulk damage in KDP crystals as a function of pulse duration, temporal profile, wavelength, and energy fluence. As previously reported by Runkel et al. 1 , we also find that the size of bulk damage sites varies roughly linearly with pulse duration for pulses between 1 ns and 9 ns. However this trend no longer applies at pulse durations below 1 ns. Experiments measuring the damage density and size distribution as a function of wavelength confirm many previous works which indicated a strong dependence of damage density with wavelength. However, we also find that the size of damage sites is relatively insensitive to wavelength. Further we see damage due to Flat-In-Time (FIT) pulses has different pulse length and fluence dependence than Gaussian pulses. We demonstrate that a simple thermal diffusion model can account for observed differences in damage densities due to square and Gaussian temporally shaped pulses of equal fluence. Moreover, we show that the key laser parameter governing size of the bulk damage sites is the length of time the pulse remains above a specific intensity. The different dependences of damage density and damage site size on laser parameters suggest different absorption mechanisms early and late in the damaging pulse

A Summary of Recent Damage-Initiation Experiments on KDP Crystals

We summarize recent investigations of the density and morphology of bulk damage in KDP crystals as a function of pulse duration, temporal profile, wavelength, and energy fluence. As previously reported by Runkel et al., we also find that the size of bulk damage sites varies roughly linearly with pulse duration for pulses between 1 ns and 9 ns. However this trend no longer applies at pulse durations below 1 ns. Experiments measuring the damage density and size distribution as a function of wavelength confirm many previous works which indicated a strong dependence of damage density with wavelength. However, we also find that the size of damage sites is relatively insensitive to wavelength. Further we see damage due to Flat-In-Time (FIT) pulses has different pulse length and fluence dependence than Gaussian pulses. We demonstrate that a simple thermal diffusion model can account for observed differences in damage densities due to square and Gaussian temporally shaped pulses of equal fluence. Moreover, we show that the key laser parameter governing size of the bulk damage sites is the length of time the pulse remains above a specific intensity. The different dependences of damage density and damage site size on laser parameters suggest different absorption mechanisms early and late in the damaging pulse

Specification of optical components using the power spectral density function

This paper describes the use of Fourier techniques to characterize the wavefront of optical components, specifically, the use of the power spectral density, (PSD), function. The PSDs of several precision optical components will be shown. Many of the optical components of interest to us have square, rectangular or irregularly shaped apertures with major dimensions up-to 800 mm. The wavefronts of components with non-circular apertures cannot be analyzed with Zernicke polynomials since these functions are an orthogonal set for circular apertures only. Furthermore, Zernicke analysis is limited to treating low frequency wavefront aberrations; mid-spatial scale and high frequency error are expressed only as ``residuals.`` A more complete and powerful representation of the optical wavefront can be obtained by Fourier analysis in 1 or 2 dimensions. The PSD is obtained from the amplitude of frequency components present in the Fourier spectrum. The PSD corresponds to the scattered intensity as a function of scattering angle in the wavefront and can be used to describe the intensity distribution at focus. The shape of a resultant wavefront or the focal spot of a complex multi-component laser system can be calculated and optimized using the PSDs of individual optical components which comprise it

Community-Acquired Klebsiella pneumoniae Bacteremia: Global Differences in Clinical Patterns

We initiated a worldwide collaborative study, including 455 episodes of bacteremia, to elucidate the clinical patterns of Klebsiella pneumoniae. Historically, community-acquired pneumonia has been consistently associated with K. pneumoniae. Only four cases of community-acquired bacteremic K. pneumoniae pneumonia were seen in the 2-year study period in the United States, Argentina, Europe, or Australia; none were in alcoholics. In contrast, 53 cases of bacteremic K. pneumoniae pneumonia were observed in South Africa and Taiwan, where an association with alcoholism persisted (p=0.007). Twenty-five cases of a distinctive syndrome consisting of K. pneumoniae bacteremia in conjunction with community-acquired liver abscess, meningitis, or endophthalmitis were observed. A distinctive form of K. pneumoniae infection, often causing liver abscess, was identified, almost exclusively in Taiwan

An improved method for undertaking limiting dilution assays for in vitro cloning of Plasmodium falciparum parasites

Abstract. Background: Obtaining single parasite clones is required for many techniques in malaria research. Cloning by limiting dilution using microscopy-based assessment for parasite growth is an arduous and labor-intensive process. An alternative method for the detection of parasite growth in limiting dilution assays is using a commercial ELISA histidine-rich protein II (HRP2) detection kit. Methods. Detection of parasite growth was undertaken using HRP2 ELISA and compared to thick film microscopy. An HRP2 protein standard was used to determine the detection threshold of the HRP2 ELISA assay, and a HRP2 release model was used to extrapolate the amount of parasite growth required for a positive result. Results: The HRP2 ELISA was more sensitive than microscopy for detecting parasite growth. The minimum level of HRP2 protein detection of the ELISA was 0.11ng/ml. Modeling of HRP2 release determined that 2,116 parasites are required to complete a full erythrocytic cycle to produce sufficient HRP2 to be detected by the ELISA. Under standard culture conditions this number of parasites is likely to be reached between 8 to 14 days of culture. Conclusions: This method provides an accurate and simple way for the detection of parasite growth in limiting dilution assays, reducing time and resources required in traditional methods. Furthermore the method uses spent culture media instead of the parasite-infected red blood cells, enabling culture to continue