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High-average-power diode-end-pumped intracavity-doubled Nd:YAG laser

Description: A compact diode-pumped ND:YAG laser was frequency-doubled to 0.532 {mu}m with an intracavity KTP or LBO crystal using a `V` cavity configuration. Two acousto-optic Q-switches were employed at repetition rates of 10-30 kHz. Dichroic fold and end mirrors were used to output two beams with up to 140 W of 0.532 {mu}m power using KTP and 116 W using LBO as the frequency doubling crystal. This corresponds to 66% of the maximum output power at 1.064 {mu}m obtained with an optimized output coupler reflectivity. The minimum output pulse duration varied with repetition rate from 90 to 130 ns. The multimode output beam had a smooth profile and a beam quality of M{sup 2} = 5 1.
Date: February 12, 1998
Creator: Honea, E.C.; Ebbers, C.A.; Beach, R.J.; Speth, J.A.; Emanuel, M.S>; Skidmore, J.A. et al.
Partner: UNT Libraries Government Documents Department

High-Throughput Laser Peening of Metals Using a High-Average-Power Nd: Glass Laser System

Description: Laser shot peening, a surface treatment for metals, is known to induce residual compressive stresses to depths of over 1 mm providing improved component resistance to various forms of failure. Recent information also suggests that thermal relaxation of the laser induced stress is significantly less than that experienced by other forms of surface stressing that involve significantly higher levels of cold work. We have developed a unique solid state laser technology employing Nd:glass amplifier slabs and SBS phase conjugation that enables this process to move into high throughput production processing.
Date: November 1, 1999
Creator: Dane, C.B.; Hackel, L.A.; Halpin, J.; Daly, J.; Harrisson, J. & Harris, J.
Partner: UNT Libraries Government Documents Department

Status of the National Ignition Facility project

Description: The ultimate goal of worldwide research in inertial confinement fusion (ICF) is to develop fusion as an inexhaustible, economic, environmentally safe source of electric power. Following nearly thirty years of laboratory and underground fusion experiments, the next step toward this goal is to demonstrate ignition and propagating burn of fusion fuel in the laboratory. The National Ignition Facility(NIF) Project is being constructed at Lawrence Livermore National Laboratory (LLNL), for just this purpose. NIF will use advanced Nd-glass laser technology to deliver 1.8 MJ of 0.35-um laser light in a shaped pulse, several nanoseconds in duration, achieving a peak power of 500 TW. A national community of U.S. laboratories is participating in this project, now in its final design phase. Franceand the United Kingdom are collaborating on development of required technology under bilateral agreements with the US. This paper presents thestatus of the laser design and development of its principal components and optical elements.
Date: April 1, 1997
Creator: Paisner, J.A.; Lowdermilk, W.H.; Boyes, J.D.; Sorem, M.S. & Soures, J.M.
Partner: UNT Libraries Government Documents Department

Diffraction-limited, high average power phase-locking of four 30J beams from discrete Nd:glass zig-zag amplifiers

Description: A single ND:YLF oscillator beam is amplified in four discrete Nd:glass, flashiamp-pumped, zig-zag amplifiers. The resulting four 30J beams are phase- locked using SBS phase conjugation, resulting in near diffraction-limited 120J pulses from a single aperture at up to a 1 OHz pulse repetition frequency.
Date: April 24, 1997
Creator: Dane, C.B.; Wintemute, J.D.; Bhachu, B. & Hackel, L.A.
Partner: UNT Libraries Government Documents Department

Spatial filter lens design for the main laser of the National Ignition Facility

Description: The National Ignition Facility 0, being designed and constructed at Lawrence Livermore National Laboratory (LLNL), comprises 192 laser beams. The lasing medium is neodymium in phosphate glass with a fundamental frequency (Ice) of 1.053~. Sum frequency generation in a pair of conversion crystals (KDP/KD*P) will produce 1.8 megajoules of the third harmonic light (30 or bO.351~) at the target. The purpose of this paper is to provide the lens design community with the current lens design details of the large powered optics in the Main Laser. This paper describes the lens design configuration and design considerations of the Main Laser. The Main Laser is 123 meters long and includes two spatial tllters: one 23.5 meters and one 60 meters. These spatial filters perform crucial beam filtering and relaying functions. We shall describe the significant lens design aspects of these spatial tilter lenses which allow them to successfully deliver the appropriate beam characteristic onto the target. For a broad overview of NIF. please see, �Optical system design of the National Ignition Facility,� by R. Edward English, et al, also found in this volume.
Date: June 26, 1998
Creator: English, R E; Korniski, R J & Miller, J L
Partner: UNT Libraries Government Documents Department

Development of a micropump for microelectronic cooling

Description: To demonstrate a system integration process for Micro-Electro-Mechanical Systems (MEMS), we are building an active cooling MEMS unit for microelectronics applications. This integrated unit will incorporate a micropump, temperature sensors, microchannels, and heat exchange devices into a single unit. The first phase of this research project is to develop and test a micropump capable of moving the working fluid within the integrated device. This paper will discuss the design, development, testing, and evaluation of a micropump concept. The micropump which was developed is an electrohydrodynamic (EHD) injection pump. Fabrication of the pump was accomplished using laser micromachining technology, and two initial designs were examined for full fabrication. The first design has two silicon parts stacked vertically on top of each other. Gold is deposited on one side of each stacked plate to serve as electrodes for the electrohydrodynamic pump. A Nd:YAG laser is used to drill an array of circular holes in the {open_quotes}well{close_quotes} region of both silicon parts, leaving an open pathway for fluid movement. Next the silicon parts are aligned and bonded together, thus becoming a EHD pump. Fluid flow has been observed when an electric voltage is applied across the electrodes. The second design has the silicon parts which contain the flow grid oriented {open_quotes}back-to-back{close_quotes} and bonded together. This {open_quotes}back-to-back{close_quotes} design has a shorter grid distance between the anode and cathode plates so that a smaller voltage is required for pumping. Preliminary results from laboratory experiments have demonstrated that this EHD micropump design can achieve a pressure head of about 287 Pa with an applied voltage of 120 V.
Date: October 1, 1996
Creator: Wong, C.C.; Adkins, D.R. & Chu, Dahwey
Partner: UNT Libraries Government Documents Department

Observation of stimulated raman scattering in an optical fiber at the Fermilab A0 photoinjector

Description: We have observed stimulated Raman scattering in a 2 km long optical fiber injected with an 81 MHz train of {approximately}80 ps pulses from a modelocked Nd:YLF oscillator operating at {lambda} = 1054 nm.
Date: September 1, 1998
Creator: Fry, A.R.; Taylor, B.; Fitch, M.J. & Melissinos, N.C., Fermilab
Partner: UNT Libraries Government Documents Department

Development of an accelerator-ready photocathode drive laser at CEBAF

Description: Many injector designs for free-electron lasers and linear colliders use photocathode sources in lieu of a thermionic cathode. These designs require mode-locked lasers with very tight phase and amplitude jitter specifications to achieve the electron beam quality needed for these applications. We have characterized the long term stability of a mode-locked laser for use in the injector test stand at CEBAF. The sources of drift and instabilities were studied and characterized. Initial results indicate that the most important source of drift is a change in the effective cavity length. A possible design for automatically optimizing the length is presented. 8 refs., 5 figs.
Date: October 1, 1996
Creator: Benson, S. & Shinn, M.
Partner: UNT Libraries Government Documents Department

Optimized, diode pumped, Nd:glass, prototype regenerative amplifier for the National Ignition Facility (NIF)

Description: The National Ignition Facility (NIF) will house a 2 MJ Nd:glass laser system to be used for a broad range of inertial confinement fusion experiments. This record high energy laser output will be initiated by a single low energy, fiber -based master oscillator which will be appropriately shaped in time and frequency prior to being split into 48 beams for intermediate amplification. These 48 intermediate energy beams will feed the 192 main amplifier chains. We report on the baseline design and test results for an amplifier subsystem in the intermediate amplifiers. The subsystem is based on a diode pumped, Nd:glass regenerative amplifier. The amplifier is comprised fo a linear, folded, TEM{sub 00}, 4.5m long cavity and represents the highest gain (approximately 10{sup 7}) component in the NIF laser system. Two fundamentally important requirements for this amplifier include output energy of 20 mJ and square pulse distortion of less than 1.45. With a single 48 bar 4.5kW peak power diode array and lens duct assembly we pump a 5 mm diameter X 50 mm long Nd-doped, phosphate glass rod, and amplify the mode matched, temporally shaped (approximately 20ns in duration)oscillator seed pulse to 25 mJof output energy with a very acceptable square pulse distortion of 1.44. This most recent design of the regenerative amplifier has increased the performance and reduced the cost, enabling it to become a solid baseline for the NIF laser system.
Date: December 1, 1997
Creator: Martinez, M.; Crane, J.; Penko, F. & Browning, D.
Partner: UNT Libraries Government Documents Department

Laser assisted non-consumable arc welding process development

Description: The employment of Laser Beam Welding (LBW) for many traditional arc welding applications is often limited by the inability of LBW to compensate for variations in the weld joint gap. This limitation is associated with fluctuations in the energy transfer efficiency along the weld joint. Since coupling of the laser beam to the workpiece is dependent on the maintenance of a stable absorption keyhole, perturbations to the weld pool can lead to decreased energy transfer and resultant weld defects. Because energy transfer in arc welding does not similarly depend on weld pool geometry, it is expected that combining these two processes together will lead to an enhanced fusion welding process that exhibits the advantages of both arc welding and LBW. Laser assisted non-consumable arc welds have been made on thin section aluminum. The welds combine the advantages of arc welding and laser welding, with enhanced penetration and fusion zone size. The use of a pulsed Nd:YAG laser with the combined process appears to be advantageous since this laser is effective in removing the aluminum oxide and thereby allowing operation with the tungsten electrode negative. The arc appears to increase the size of the weld and also to mitigate hot cracking tendencies that are common with the pulsed Nd:YAG laser.
Date: September 1, 1997
Creator: Fuerschach, P.W. & Hooper, F.M.
Partner: UNT Libraries Government Documents Department

National Ignition Facility for Inertial Confinement Fusion

Description: The National Ignition Facility for inertial confinement fusion will contain a 1.8 MJ, 500 TW frequency-tripled neodymium glass laser system that will be used to explore fusion ignition and other problems in the physics of high temperature and density. We describe the facility briefly. The NIF is scheduled to be completed in 2003.
Date: October 8, 1997
Creator: Paisner, J.A. & Murray, J.R.
Partner: UNT Libraries Government Documents Department

High gain preamplifier module (PAM) engineering prototype for the National Ignition Facility (NIF) laser system

Description: We describe recent results and developments in the preamplifier module (PAM) engineering prototype located in NIF� s front end or Optical Pulse Generation (OPG) system. This prototype uses the general laser design developed on a physics testbed and integrates NIP type packaging as well as controls and diagnostics. We will present laser, mechanical and electrical hardware designed and built to date as well as laser energetics measurements.
Date: October 29, 1998
Creator: Braucht, J; Browning, D; Crane, J K; Crawford, J; Deadrick, F J; Hawkins, S et al.
Partner: UNT Libraries Government Documents Department

Design and performance of the main amplifier system for the National Ignition Facility

Description: This paper describes the design and performance of flashlamp-pumped, Nd:glass. Brewster-angle slab amplifiers intended to be deployed in the National Ignition Facility (NIF). To verify performance, we tested a full-size, three-slab-long, NIF prototype amplifier, which we believe to be the largest flashlamp-pumped Nd:glass amplifier ever assembled. Like the NIF amplifier design, this prototype amplifier had eight 40-cm-square apertures combined in a four-aperture-high by two-aperture-wide matrix. Specially-shaped reflectors, anti-reflective coatings on the blastshields, and preionized flashlamps were used to increase storage efficiency. Cooling gas was flowed over the flashlamps to remove waste pump heat and to accelerate thermal wavefront recovery. The prototype gain results are consistent with model predictions and provide high confidence in the final engineering design of the NIF amplifiers. Although the dimensions, internal positions, and shapes of the components in the NIF amplifiers will be slightly different from the prototype, these differences are small and should produce only slight differences in amplifier performance
Date: February 16, 1999
Creator: Beullier, J; Erlandson, A; Grebot, E; Guenet, J; Guenet, M; Horvath, J et al.
Partner: UNT Libraries Government Documents Department

Laser engineered net shaping (LENS) for the fabrication of metallic components

Description: Solid free form fabrication is a fast growing automated manufacturing technology that has reduced the time between initial concept and fabrication. Starting with CAD renditions of new components, techniques such as stereolithography and selective laser sintering are being used to fabricate highly accurate complex 3-D objects using polymers. Together with investment casting, sacrificial polymeric objects are used to minimize cost and time to fabricate tooling used to make complex metal casting. This paper describes recent developments in LENS{trademark} (Laser Engineered Net Shaping) to fabricate the metal components {ital directly} from CAD solid models and thus further reduce the lead time. Like stereolithography or selective sintering, LENS builds metal parts line by line and layer by layer. Metal particles are injected into a laser beam where they are melted and deposited onto a substrate as a miniature weld pool. The trace of the laser beam on the substrate is driven by the definition of CAD models until the desired net-shaped densified metal component is produced.
Date: June 1, 1996
Creator: Griffith, M.L.; Keicher, D.L.; Romero, J.A.; Atwood, C.L.; Harwell, L.D.; Greene, D.L. et al.
Partner: UNT Libraries Government Documents Department

A diode-pumped channel waveguide laser fabricated in Nd: phosphate glass

Description: We report on the laser performance of a Nd:phosphate glass (Nd:IOG-1) channel waveguide laser fabricated by electric field assisted Ag{sup +} diffusion. Lasing was achieved in two different size channels, 29 x 9 {micro}m{sup 2} and 50 x 9 {micro}m{sup 2}, on a sample of length 8 mm. Slope efficiencies of {approximately} 15% with respect to incident pump power were measured. Losses in the 29 um wide channel were measured to be in the range 0.2--1.1 dB/cm and in the 50 mm channel, 0.2--0.4 dB/cm. The laser spectrum, centered about the emission peak of 1053 nm, was multimode and randomly polarized.
Date: January 29, 1999
Creator: Patel, F D; Honea, E C; Krol, D; Payne, S A & Hayden, J
Partner: UNT Libraries Government Documents Department

Thermal analysis of the large close packed amplifiers in the National Ignition Facility (NIF)

Description: Flashlamp pumping of the large aperture multi-segment NIF amplifiers will result in large amounts of energy being deposited as heat in the amplifier components. The magnitude of the heating and the nonuniform distribution result in a delay time between shots due to wavefront distortion and steering error. A NEF requirement is that the thermal wavefront recovery must occur in less than six hours. The principal cause of long-term wavefront distortion is the thermal gradient produced in the slab as heat diffuses from the edge cladding into the pumped volume. Thermal equilibrium is established through conduction, convection, and exchange of thermal radiation. Radiative exchange between glass components, such as flashlamps, blast shields, and laser slabs is especially effective because of the large surface areas of these components and the high emissivity of the glass. Free convection within the amplifier enclosure is also important but is on the order of a 10 to 20% effect compared to radiation for the major surfaces. To evaluate the NIF design, the amplifier was modeled to calculate the thermal response of a single laser element. The amplifier is cooled by flowing room-temperature air or nitrogen through the flashlamp cassettes. Active cooling of the flashlamps and blast shields serves two purposes; the energy deposited in these components can be removed before it is transferred to the amplifier optical components, and the cooled blast shield provides a large area heat sink for removal of the residual heat from the laser slabs. Approximately 50 to 60% of the flashlamp energy is deposited in the flashlamps and blast shields. Thus, cooling the flashlamp cassette is a very effective method for removing a substantial fraction of the energy without disturbing the optical elements of the system. Preliminary thermal analysis indicates that active cooling with flow rates of 10 CFM per flashlamp ...
Date: May 1, 1995
Creator: Brown, D.L. & Mannell, G.T.
Partner: UNT Libraries Government Documents Department

Optically induced surface flashover switching for the dielectric wall accelerator

Description: Fast, low jitter command triggered switching is key to the successful implementation of the dielectric wall accelerator (DWA). We are studying a UV induced vacuum surface flashover switch for this purpose. We present our initial data using a Nd:YAG laser incident onto a high gradient insulator surface at 1{omega}, 2{omega}, and 4{omega}. Best 1{sigma} jitter was <1 ns with no degradation of the switch after 500 shots.
Date: April 27, 1995
Creator: Sampayan, S.; Caporaso, G.; Carder, B.; Norton, M.; Trimble, D. & Elizondo, J.
Partner: UNT Libraries Government Documents Department

Small-business technology transfer program, case number 93119 - second harmonic generation for Lee Laser Inc.: Resonator designs

Description: The author has investigated several resonator designs for Lee Laser Inc. as outlined in the Short-Term Technical Assistance Project, case number 93119. The scope of this work was to identify various resonator options which would be suitable for use in an intra-cavity doubled Nd:YAG laser and compatible with Lee Laser hardware. This work consisted of computer modeling of laser resonators to identify mirror curvatures, distances, beam sizes, and sensitivity to thermal loading of the laser rod.
Date: September 2, 1994
Creator: Erbert, G.V.
Partner: UNT Libraries Government Documents Department