S. Sutton

National Ignition Facility laser performance status

The National Ignition Facility (NIF) is the worlds largest laser system. It contains a 192 beam neodymium glass laser that is designed to deliver 1.8 MJ at 500 TW at 351 nm in order to achieve energy gain (ignition) in a deuterium-tritium nuclear fusion target. To meet this goal, laser design criteria include the ability to generate pulses of up to 1.8 MJ total energy, with peak power of 500 TW and temporal pulse shapes spanning 2 orders of magnitude at the third harmonic (351 nm or 3omega) of the laser wavelength. The focal-spot fluence distribution of these pulses is carefully controlled, through a combination of special optics in the 1omega (1053 nm) portion of the laser (continuous phase plates), smoothing by spectral dispersion, and the overlapping of multiple beams with orthogonal polarization (polarization smoothing). We report performance qualification tests of the first eight beams of the NIF laser. Measurements are reported at both 1omega and 3omega, both with and without focal-spot conditioning. When scaled to full 192 beam operation, these results demonstrate, to the best of our knowledge for the first time, that the NIF will meet its laser performance design criteria, and that the NIF can simultaneously meet the temporal pulse shaping, focal-spot conditioning, and peak power requirements for two candidate indirect drive ignition designs.

The mercury project : A high average power, gas-cooled laser for inertial fusion energy development

Abstract Hundred-joule, kilowatt-class lasers based on diode-pumped solid-state technologies, are being developed worldwide for laser-plasma interactions and as prototypes for fusion energy drivers. The goal of the Mercury Laser Project is to develop key technologies within an architectural framework that demonstrates basic building blocks for scaling to larger multi-kilojoule systems for inertial fusion energy (IFE) applications. Mercury has requirements that include: scalability to IFE beamlines, 10 Hz repetition rate, high efficiency, and 109 shot reliability. The Mercury laser has operated continuously for several hours at 55 J and 10 Hz with fourteen 4 × 6 cm2 ytterbium doped strontium fluoroapatite amplifier slabs pumped by eight 100 kW diode arrays. A portion of the output 1047 nm was converted to 523 nm at 160 W average power with 73 % conversion efficiency using yttrium calcium oxy-borate (YCOB).

High-average-power femto-petawatt laser pumped by the Mercury laser facility

The Mercury laser system is a diode-pumped solid-state laser that has demonstrated over 60 J at a repetition rate of 10 Hz (600 W) of near-infrared light (1047 nm). Using a yttrium calcium oxyborate frequency converter, we have demonstrated 31.7 J/pulse at 10 Hz of second harmonic generation. The frequency converted Mercury laser system will pump a high-average-power Ti:sapphire chirped pulse amplifier system that will produce a compressed peak power > 1 PW and peak irradiance > 1023W/cm2.

Compact, Efficient Laser Systems Required for Laser Inertial Fusion Energy

Abstract This paper presents our conceptual design for laser drivers used in Laser Inertial Fusion Energy (LIFE) power plants. Although we have used only modest extensions of existing laser technology to ensure near-term feasibility, predicted performance meets or exceeds plant requirements: 2.2 MJ pulse energy produced by 384 beamlines at 16 Hz, with 18% wall-plug efficiency. High reliability and maintainability are achieved by mounting components in compact line-replaceable units that can be removed and replaced rapidly while other beamlines continue to operate, at up to ˜13% above normal energy, to compensate for neighboring beamlines that have failed. Statistical modeling predicts that laser-system availability can be greater than 99% provided that components meet reasonable mean-time-between-failure specifications.

1-W average power levels and tunability from a diode-pumped 2.94-μm Er:YAG oscillator

A tunable Er:YAG laser, side pumped by a quasi-cw InGaAs diode array, generates > 500 mW of power at 2.936 microm. The cavity is a 4-cm plano-concave resonator that uses total internal reflection on the pump face of the Er:YAG crystal to couple the diode emission into the resonating modes of the oscillator. Tuning is accomplished by angle tuning a 300-microm-thick YAG étalon. The tuning range is 2.933-2.939 microm. Thermal lensing limits the duty factor to 4% or 8%, depending on the Er:YAG crystal thickness (2 or 1 mm). A 2.5-cm-long resonator operates at an 11% duty factor and generates 1.3 W of average power.

Solid state heat capacity disk laser

This paper describes a solid state laser concept that scales to MW levels of burst power and MJ of burst energy and burst durations measured in seconds. During lasing action, waste heat is purposely stored in the heat capacity of the active medium. The paper outlines the principal scaling laws of key operational features and arrives at a conceptual design example of the laser head as well as a mobile laser system.

ND:GLASS LASER DESIGN FOR LASER ICF FISSION ENERGY (LIFE)

Abstract We have developed preliminary conceptual laser system designs for the Laser ICF (Inertial Confinement Fusion) Fission Energy (LIFE) application. Our approach leverages experience in high-energy Nd: glass laser technology developed for the National Ignition Facility (NIF)1, along with high-energy-class diode-pumped solid-state laser (HEC-DPSSL) technology developed for the DOE’s High Average Power Laser (HAPL) Program and embodied LLNL’s Mercury laser system.2 We present laser system designs suitable for both indirect-drive, hot spot ignition and indirect-drive, fast ignition targets. Main amplifiers for both systems use laser-diode-pumped Nd:glass slabs oriented at Brewster’s angle, as in NIF, but the slabs are much thinner to allow for cooling by high-velocity helium gas as in the Mercury laser system. We also describe a plan to mass-produce pump-diode lasers to bring diode costs down to the order of

The National Ignition Facility 2007 laser performance status

0.01 per Watt of peak output power, as needed to make the LIFE application economically attractive.

A Laser Technology Test Facility for Laser Inertial Fusion Energy (LIFE)

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory contains a 192-beam 3.6 MJ neodymium glass laser that is frequency converted to 351nm light. It has been designed to support high energy density science (HEDS), including the demonstration of fusion ignition through Inertial Confinement. To meet this goal, laser design criteria include the ability to generate pulses of up to 1.8-MJ total energy at 351nm, with peak power of 500 TW and precisely-controlled temporal pulse shapes spanning two orders of magnitude. The focal spot fluence distribution of these pulses is conditioned, through a combination of special optics in the 1ω (1053 nm) portion of the laser (continuous phase plates), smoothing by spectral dispersion (SSD), and the overlapping of multiple beams with orthogonal polarization (polarization smoothing). In 2006 and 2007, a series of measurements were performed on the NIF laser, at both 1ω and 3ω (351 nm). When scaled to full 192-beam operation, these results lend confidence to the claim that NIF will meet its laser performance design criteria and that it will be able to simultaneously deliver the temporal pulse shaping, focal spot conditioning, peak power, shot-to-shot reproducibility, and power balance requirements of indirect-drive fusion ignition campaigns. We discuss the plans and status of NIFs commissioning, and the nature and results of these measurement campaigns.

Diode-Pumped Solid-State Lasers for Inertial Fusion Energy

A LIFE laser driver needs to be designed and operated which meets the rigorous requirements of the NIF laser system while operating at high average power, and operate for a lifetime of >30 years. Ignition on NIF will serve to demonstrate laser driver functionality, operation of the Mercury laser system at LLNL demonstrates the ability of a diode-pumped solid-state laser to run at high average power, but the operational lifetime >30 yrs remains to be proven. A Laser Technology test Facility (LTF) has been designed to specifically address this issue. The LTF is a 100-Hz diode-pumped solid-state laser system intended for accelerated testing of the diodes, gain media, optics, frequency converters and final optics, providing system statistics for billion shot class tests. These statistics will be utilized for material and technology development as well as economic and reliability models for LIFE laser drivers.