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Design of precision mounts for optimizing the conversion efficiency of KDP crystals for the National Ignition Facility

Description: A key design challenge for the National Ignition Facility (NIF), being constructed at Lawrence Livermore National Laboratory (LLNL), [Hibbard, R L , 1998], is the frequency converter consisting of two KDP crystals and a focusing lens Frequency conversion is a critical performance factor for NIF and the optical mount design for this plays a key role in meeting design specifications The frequency converter is a monolithic cell that mounts the optics and is the point on the beamline where the frequency conversion crystals are optimally aligned and the cell is focused on target The lasing medium is neodymium in phosphate glass with a fundamental frequency (1{omega}) of 1 053 {micro}m Sum frequency generation in a pair of conversion crystals (KDP/KD*P) produces 1 8 MJ of the third harmonic light (3{omega} or {lambda}=O 35 pm). The phase-matching scheme on NIF is type I second harmonic generation followed by type II sum-frequency-mixing of the residual fundamental and the second harmonic light This laser unlike previous laser system designs, must achieve high conversion efficiency, 85%, which is close to the 90 8% theoretical maximum As a result, this design is very sensitive to angular variations in beam propagation and in the crystal axes orientation. Factors that influence the phase matching angle include crystal inhomogeneity, residual and induced stress in the crystals, the crystals` natural and mounted surface figure, mounting imperfections and gravity sag These angular variations need to be controlled within a 40 {micro}rad error budget. The optical mount contributions to the angular error budget are 20 {micro}rad and are what make the frequency converter in the Final Optics Cell (FOC) such a challenging precision design. The premise of using full edge support in the FOC design is primarily driven by the spherical target chamber design that has optics mounted at multiple longitudinal ...
Date: March 30, 1998
Creator: Hibbard, R. L.
Partner: UNT Libraries Government Documents Department

A Flexure-Based Tool Holder for Sub-(micro)m Positioning of a Single Point Cutting Tool on a Four-axis Lathe

Description: A tool holder was designed to facilitate the machining of precision meso-scale components with complex three-dimensional shapes with sub-{micro}m accuracy on a four-axis lathe. A four-axis lathe incorporates a rotary table that allows the cutting tool to swivel with respect to the workpiece to enable the machining of complex workpiece forms, and accurately machining complex meso-scale parts often requires that the cutting tool be aligned precisely along the axis of rotation of the rotary table. The tool holder designed in this study has greatly simplified the process of setting the tool in the correct location with sub-{micro}m precision. The tool holder adjusts the tool position using flexures that were designed using finite element analyses. Two flexures adjust the lateral position of the tool to align the center of the nose of the tool with the axis of rotation of the B-axis, and another flexure adjusts the height of the tool. The flexures are driven by manual micrometer adjusters, each of which provides a minimum increment of motion of 20 nm. This tool holder has simplified the process of setting a tool with sub-{micro}m accuracy, and it has significantly reduced the time required to set a tool.
Date: December 5, 2005
Creator: Bono, M J & Hibbard, R L
Partner: UNT Libraries Government Documents Department

CAVE: the design of a precision metrology instrument for studying performance of KDP crystals

Description: A device has been developed to measure the frequency conversion performance of large aperture potassium dihydrogen phosphate (KDP) crystals. Third harmonic generation using ICDP is critical to the function of the National Ignition Facility (NIF) laser. The crystals in the converter can be angularly or thermally tuned but are subject to larger aperture inhomogeneities that are functions of growth manufacturing and - mounting. The CAVE (Crystal Alignment Verification Equipment) instrument scans the crystals in a thermally and mechanically controlled environment to determine the local peak tuning angles. The CAVE can then estimate the optimum tuning angle and conversion efficiency over the entire aperture. Coupled with other metrology techniques, the CAVE will help determine which crystal life-cycle components most affect harmonic conversion.
Date: March 30, 1998
Creator: Hibbard, R.L., LLNL
Partner: UNT Libraries Government Documents Department

Machining, Assembly, and Characterization of a Meso-Scale Double Shell Target

Description: Several issues related to the manufacture of precision meso-scale assemblies have been identified as part of an effort to fabricate an assembly consisting of machined polymer hemispherical shells and machined aerogel. The assembly, a double shell laser target, is composed of concentric spherical layers that were machined on a lathe and then assembled. This production effort revealed several meso-scale manufacturing techniques that worked well, such as the machining of aerogel with cutting tools to form low density structures, and the development of an assembly manipulator that allows control of the assembly forces to within a few milliNewtons. Limitations on the use of vacuum chucks for meso-scale components were also identified. Many of the lessons learned in this effort are not specific to double shell targets and may be relevant to the production of other meso-scale devices.
Date: October 21, 2003
Creator: Bono, M J & Hibbard, R L
Partner: UNT Libraries Government Documents Department

Effect of radiant energy on vaporization and combustion of liquid fuels

Description: Report presenting an investigation of the radiative processes involved in combustion to determine the present role of radiant energy transfer in combustors. The equivalent gray-body emissivity of a hydrocarbon fuel may be increased by use of liquid or solid, soluble or nonsoluble, additives. Results regarding the experimental apparatus and methods, emission characteristics of luminous and nonluminous flames, absorptivity of fuels and of solutions of possible additives, and absorption by slurries are provided.
Date: November 13, 1952
Creator: Berlad, A. L. & Hibbard, R. R.
Partner: UNT Libraries Government Documents Department

Solubility of water in hydrocarbons

Description: Report presenting a study of the literature data on the solubility of water in hydrocarbons, which includes information about the log of solubility, critical solution temperature, and ratios that may affect solubility are provided. An equation is presented and applied to a few petroleum fractions ranging from gasoline to lubricating oil, and a comparison of calculated and experimental solubilities is provided.
Date: July 10, 1952
Creator: Hibbard, R. R. & Schalla, R. L.
Partner: UNT Libraries Government Documents Department

Fabrication of Planar Laser Targets with Sub-Micrometer Thickness Uniformity

Description: Lawrence Livermore National Laboratory routinely manufactures planar laser targets that consist of stacked and bonded foils for physics experiments on high-energy lasers. One recent planar laser target, the Equation of State target, had extremely tight specifications. The target required four bonded layers with thickness uniformities of several hundred nm, and the adhesive bonds between the layers could not exceed a few {micro}m. This paper describes the manufacturing process that was developed to meet these specifications.
Date: July 21, 2005
Creator: Bono, M J; Castro, C & Hibbard, R L
Partner: UNT Libraries Government Documents Department

Development of a Manufacturing Process for High-Precision Cu EOS Targets

Description: This document describes the development of a manufacturing process and the production of Cu EOS targets. The development of a manufacturing process for these targets required a great deal of research, because the specifications for the targets required a level of precision an order of magnitude beyond Target Fabrication's capabilities at the time. Strict limitations on the dimensions of the components and the interfaces between them required research efforts to develop bonding and deposition processes consistent with a manufacturing plan with a dimensional precision on the order of 0.1 {micro}m. Several months into this effort, the specifications for the targets were relaxed slightly as a result of discussions between the Target Fabrication Group and the physicists. The level of precision required for these targets remained an order of magnitude beyond previous capabilities, but the changes made it possible to manufacture targets to the specifications. The development efforts and manufacturing processes described in this document successfully produced a complete Cu EOS target that satisfied all of the fabrication and metrology specifications.
Date: January 12, 2006
Creator: Bono, M J; Castro, C & Hibbard, R L
Partner: UNT Libraries Government Documents Department


Description: Many commercial metrology systems exist for making accurate surface form and roughness measurements of nominally planar parts. However, few metrology systems exist for making accurate absolute thickness measurements. At Lawrence Livermore National Laboratory there is an increasing need for absolute thickness measurements of mesoscale parts ranging in size from 1 mm to 25 mm in diameter and 2 {micro}m to 500 {micro}m thickness. The samples of interest in this case are nominally planar parts that require absolute thickness to be known to an accuracy of better than one micrometer. An Absolute Thickness Measurement Machine (ATMM) has been designed and constructed to fulfill this requirement (see Figure 1). This article describes the design of the ATMM and the theory behind its operation including a detailed error budget. Other issues discussed involve errors associated with the sensors (non-linearity, and sensor resolution), development of the stepped thickness reference, thermal effects, and future upgrades. This research represents one of many issues involving meso-scale metrology currently under development at Lawrence Livermore National Laboratory.
Date: July 27, 2005
Creator: Nederbragt, W.; Hibbard, R.; Kroll, J. & Kelly, D.
Partner: UNT Libraries Government Documents Department

Dilution of liquid oxygen when nitrogen is used for pressurization

Description: Report presenting a graphic method for determining the composition and phases within a propellant tank when liquid oxygen is pressurized with nitrogen gas and some of the calculations involved. The assumed limiting conditions are that pressurizing gas flows adiabatically from the pressure tank and that equilibrium exists in the oxygen-nitrogen system. The experiment indicates that a series dilution of the oxidant occurs when nitrogen is used as a pressurizing gas, but a barrier at the liquid-gas interface would permit the use of nitrogen.
Date: April 1, 1958
Creator: Walsh, Thomas J.; Hibbard, R. R. & Ordin, Paul M.
Partner: UNT Libraries Government Documents Department

Frequency converter design and manufacturing considerations for the National Ignition Facility

Description: The National Ignition Facility (NIF), being constructed at Lawrence Livermore National Laboratory (LLNL), comprises 192 laser beams, Figure 1. The lasing medium is neodymium in phosphate glass with a fundamental frequency (1{omega}) of 1.053 {micro}m. Sum frequency generation in a pair of conversion crystals (KDP/KD*P) produces 1.8 Mj of the third harmonic light (3{omega} or {lambda}=0.35). On NIF the frequency conversion crystals are part of the Final Optics Assembly (FOA), whose two principal functions are to convert the laser light to 3{omega} and focus it on target. In addition, the FOA provides a vacuum window to the target chamber, smoothes the on- target irradiance profile, moves the unconverted light away from the target, and provides signals for alignment and diagnostics. The FOA has four Integrated Optics Modules (IOM), Figure 4, each of which contains two 41 cm square crystals are mounted with the full edge support to micro radian angular and micron flatness tolerances. This paper is intended to be an overview of the important factors that affect frequency conversion on NIF. Chief among these are angular errors arising from crystal growth, finishing, and mounting. The general nature of these errors and how they affect frequency conversion, and finally the importance of a frequency conversion metrology tool in assessing converter performance before opto-mechanical assemblies are installed on NIF will be discussed.
Date: March 25, 1998
Creator: Hibbard, R.L.; English, R.E., Jr.; De Yoreo, J.J. & Montesanti, R.C.
Partner: UNT Libraries Government Documents Department

Hohlraum-driven ignition-like double-shell implosions on the Omega laser facility

Description: High-convergence ignition-like double-shell implosion experiments have been performed on the Omega laser facility [T.R. Boehly et al., Opt. Commun. 133, 495 (1997)] using cylindrical gold hohlraums with 40 drive beams. Repeatable, dominant primary (2.45 MeV) neutron production from the mix-susceptible compressional phase of a double-shell implosion, using fall-line design optimization and exacting fabrication standards, is experimentally inferred from time-resolved core x-ray imaging. Effective control of fuel-pusher mix during final compression is essential for achieving noncryogenic ignition with double-shell targets on the National Ignition Facility [Paisner et al., Laser Focus World 30, 75 (1994)].
Date: October 1, 2004
Creator: Amendt, P; Robey, H F; Park, H S; Tipton, R E; Turner, R E; Milovich, J L et al.
Partner: UNT Libraries Government Documents Department

Development of a metrology instrument for mapping the crystallographic axis in large optics

Description: A metrology instrument has been developed to scan crystals and map the peak tuning angles for frequency conversion from the infrared to the ultra violet over large apertures. The need for such a device emerged from the National Ignition Facility (NIF) program where frequency conversion crystals have been found to have significant crystallographic axis wander at the large NIF aperture size of 4 1 cm square. With only limited access to a large aperture laser system capable of testing these crystals, scientists have been unable to determine which crystal life-cycle components most affect these angular anomalies. A system that can scan crystals with a small diameter probe laser beam and deliver microradian accuracy and repeatability from probe point to probe point is needed. The Crystal Alignment Verification Equipment (CAVE) is the instrument designed to meet these needs and fit into the budget and time constraints of the ongoing NIF development. In order to measure NIF crystals, the CAVE has a workspace of 50 x 50 cm and an angular measurement accuracy of 10 {micro}radians. Other precision requirements are probe beam energy measurement to 2% of peak, thermal control to 20 0. 1°C around the crystal, crystal mounting surface flatness of 1 {micro}m over 40 cm square, and clean operations to Class 100 standards. Crystals are measured in a vertical position in a kinematic mount capable of tuning the crystal to 1 {micro}radian. The mirrors steering the probe beam can be aligned to the same precision. Making tip/tilt mounts with microradian level adjustment is relatively commonplace. The real precision engineering challenge of the CAVE system is maintaining the angular alignment accuracy of the probe laser relative to the crystal for each spatial position to be measured. The design team determined that a precision XY stage with the required workspace and angular ...
Date: October 21, 1998
Creator: Hibbard, R L; Liou, L W; Michie, R B & Summers, M D
Partner: UNT Libraries Government Documents Department

Fabrication of Double Shell Targets with a Glass Inner Capsule Supported by SiO2 Aerogel for Shots on the Omega Laser in 2006

Description: Indirectly driven double shell implosions are being investigated as a possible noncryogenic path to ignition on the National Ignition Facility. Lawrence Livermore National Laboratory has made several technological advances that have produced double shell targets that represent a significant improvement to previously fielded targets. The inner capsule is supported inside the ablator shell by SiO{sub 2} aerogel with a nominal density of 50 mg/cm{sup 3}. The aerogel is cast around the inner capsule and then machined concentric to it. The seamless sphere of aerogel containing the embedded capsule is then assembled between the two halves of the ablator shell. The concentricity between the two shells has been improved to less than 1.5 {micro}m. The ablator shell consists of two hemispherical shells that mate at a step joint that incorporates a gap with a nominal thickness of 0.1 {micro}m. Using a new flexure-based tool holder that precisely positions the diamond cutting tool on the diamond turning machine, step discontinuities on the inner surface of the ablator of less than 0.5 {micro}m have been achieved. New methods have been used to comprehensively characterize each of the targets using high-resolution x-ray imaging systems.
Date: October 26, 2006
Creator: Bono, M; Bennett, D; Castro, C; Satcher, J; Poco, J; Brown, W et al.
Partner: UNT Libraries Government Documents Department

Frequency converter development for the National Ignition Facility

Description: The design of the National Ignition Facility (NIF) incorporates a type I/type II third harmonic generator to convert the 1.053-{micro}m fundamental wavelength of the laser amplifier to a wavelength of 0.351 {micro}m for target irradiation. To understand and control the tolerances in the converter design, we have developed a comprehensive error budget that accounts for effects that are known to influence conversion efficiency, including variations in amplitude and phase of the incident laser pulse, temporal bandwidth of the incident laser pulse, crystal surface figure and bulk non-uniformities, angular alignment errors, Fresnel losses, polarization errors and crystal temperature variations. The error budget provides specifications for the detailed design of the NIF final optics assembly (FOA) and the fabrication of optical components. Validation is accomplished through both modeling and measurement, including full-scale Beamlet tests of a 37-cm aperture frequency converter in a NIF prototype final optics cell. The prototype cell incorporates full-perimeter clamping to support the crystals, and resides in a vacuum environment as per the NIF design.
Date: October 30, 1998
Creator: Auerbach, J M; Barker, C E; Burkhart, S C; Couture, S A; DeYoreo, J J; Hackel, L A et al.
Partner: UNT Libraries Government Documents Department

Modeling of frequency doubling and tripling with converter refractive index spatial non-uniformities due to gravitational sag

Description: Accurate predictions of the performance of frequency conversion requires knowledge of the spatial variation of departures from the phase-matching condition in the converter crystals. This variation is caused by processes such as crystal growth and crystal surface finishing. Gravitational sag and mounting configurations also lead to deformation and stresses which cause spatially varying departures from the phase-matching condition. We have modeled the effect of gravitational forces on conversion efficiency performance of horizontal converter crystals and have shown for the NIF mounting configurations that gravity has very little effect on conversion efficiency. Keywords: Frequency conversion, ICF, Nonlinear optics, KDP crystals
Date: August 3, 1998
Creator: De Yoreo, J J; Auerbach, J M; Barker, C E; Couture, S A; Eimerl, D; Hackel, L A et al.
Partner: UNT Libraries Government Documents Department

Measuring parameters of large-aperture crystals used for generating optical harmonics

Description: The purpose of this project was to develop tools for understanding the influence of crystal quality and crystal mounting on harmonic-generation efficiency at high irradiance. Measuring the homogeneity of crystals interferometrically, making detailed physics calculations of conversion efficiency, performing finite- element modeling of mounted crystals, and designing a new optical metrology tool were key elements in obtaining that understanding. For this work, we used the following frequency-tripling scheme: type I second- harmonic generation followed by type II sum-frequency mixing of the residual fundamental and the second harmonic light. The doubler was potassium dihydrogen phosphate (KDP), and the tripler was deuterated KDP (KD*P). With this scheme, near-infrared light (1053 nm) can be frequency tripled (to 351 nm) at high efficiency (theoretically >90%) for high irradiance (>3 GW/cm&sup2;). Spatial variations in the birefringence of the large crystals studied here (37 to 41 cm square by about 1 cm thick) imply that the ideal phase-matching orientation of the crystal with respect to the incident laser beam varies across the crystal. We have shown that phase-measuring interferometry can be used to measure these spatial variations. We observed transmitted wavefront differences between orthogonally polarized interferograms of {lambda}/50 to {lambda}/100, which correspond to index variations of order 10<sup>-6</sup>. On some plates that we measured, the standard deviation of angular errors is 22-23 &micro;rad; this corresponds to a 1% reduction in efficiency. Because these conversion crystals are relatively thin, their surfaces are not flat (deviate by k2.5 urn from flat). A crystal is mounted against a precision-machined surface that supports the crystal on four edges. This mounting surface is not flat either (deviates by +2.5 &micro;m from flat). A retaining flange presses a compliant element against the crystal. The load thus applied near the edges of the crystal surface holds it in place. We performed detailed finite-element ...
Date: February 23, 1999
Creator: Auerbach, J M; English, R E, Jr; Hibbard, R L; Michie, R B; Norton, M A; Perfect, S A et al.
Partner: UNT Libraries Government Documents Department

Demonstartion of density dependence of x-ray flux in a laser-driven hohlraum

Description: Experiments have been conducted using laser-driven cylindrical hohlraums whose walls are machined from Ta{sub 2}O{sub 5} foams of 100 mg/cc and 4 g/cc densities. Measurements of the radiation temperature demonstrate that the lower density walls produce higher radiation temperatures than the high density walls. This is the first experimental demonstration of the prediction that this would occur [M. D. Rosen and J. H. Hammer, Phys. Rev. E 72, 056403 (2005)]. For high density walls, the radiation front propagates subsonically, and part of the absorbed energy is wasted by the flow kinetic energy. For the lower wall density, the front velocity is supersonic and can devote almost all of the absorbed energy to heating the wall.
Date: February 11, 2008
Creator: Young, P E; Rosen, M D; Hammer, J H; Hsing, W S; Glendinning, S G; Turner, R E et al.
Partner: UNT Libraries Government Documents Department