Parameter Optimization of 1-D Multi-FM SSD on the NIF (original) (raw)

Optical system design of the National Ignition Facility

International Optical Design Conference, 1998

The National Ignition Facility (NIF) is a laser fusion facility being constructed at Lawrence Liver-more National Laboratory (LLNL). The neodymium-doped phosphate glass pulsed laser system will produce over 3.5MJ of laser energy at a fundamental lasing wavelength of 1.053pm (1 o). The final optics assembly contains a pair of crystals (KDPKD*P) and a focusing lens to convert the light by sum-frequency-mixing to 30 (h=0,35pm) and focus 1 .SM.J onto the target. The NIF optical system is large and complex. To give some perspective the NIF building is roughly 200 meters long x 85 meters wide. There are approximately 7500 optical components in the large aperture laser system-lenses, mirrors, polarizers, laser slabs, crystals, and windowseach with a clear aperture greater than 4Ocm square. The front-end of the laser system contains more than 8000 smaller (S-l 5cm) precision laser components. In this paper we will describe the optical system configuration, layout, and general design considerations. We will explain the path of the pulse through the various subsystems. Some of the top-level optical system and subsystem design requirements will be presented.

Laser-induced dispersion control

CLEO: 2014, 2014

An intense laser pulse is used to control the spectral phase of a weak probe pulse as they overlap in fused silica. The laser-induced linear chirp is controlled by the delay time between pulses. Dependence from intensity and spectral phase of the pump pulse is also studied. Experimental data is validated by numerical simulation based on optical Kerr effect. Results show that laser-induced pulse shaping is possible and may be useful for intracavity pulse compression and shaping in enhancement cavities.

Automation of NIF Target Characterization and Laser Ablation of Domes Using the 4pi System

Fusion Science and Technology, 2015

Capsules for inertial confinement fusion require precise measurement of isolated features and domes on the capsule's outer surface. Features that are too large must be removed. A 4pi capsule mapping and characterization system has been developed to map, identify, and measure domes using a Leica confocal microscope. An ultraviolet wavelength laser was integrated to laserablate the offending domes that exceed the allowable mix mass. Current process methods to remove domes require three different stations in different locations. The 4pi system achieves automated capsule handling, metrology, and laser polishing/ablation of domes on one device without losing track of the capsule's orientation. The measurement technique and metrology accuracy are compared to patch atomic force microscopy scans and phase-shifting diffraction interferometer measurements with good correlation. The laser polishing method has demonstrated analogous results to the current process methods, but in an automated fashion. Additionally, the 4pi capsule-handling capability of the system has been used to laser-ablate purposeful engineered designs into specialty capsules.

The National Ignition Facility Front-End Laser System

The proposed National Ignition Facility is a 192 beam Nd:glass laser system capable of driving targets to fusion ignition by the year 2005. A key factor in the flexibility and performance of the laser is a front-end system which provides a precisely formatted beam to each beamline. Each of the injected beams has individually controlled energy, temporal pulseshape, and spatial shape to accommodate beamline-to-beamline variations in gain and saturation. This flexibility also gives target designers the options for precisely controlling the drive to different areas of the target. The design of the Front-End laser is described, and initial results are discussed. 1. OVERVIEW The National Ignition Facility (NIP) consists of a 192 beam high-energy glass laser system and target chamber, intended for inertial confinement fusion research. Each beam originates from the Front-End as a nominal 1.7 J, 20 ns pulse at. This temporally and spatially modulated pulse is injected into the main laser amplifier, boosted to 17.2 U, frequency tripled, and directed onto the fusion target. Advances in fiber oscillators and amplifiers, temporal modulation, diode and flashlamp-pumped rod amplifiers, and spatial beam shaping are required to successfully generate the laser pulse for NIF. In Fig. 1 we show the block diagram of the Front-End laser. We use four oscillators to provide four separate wavelengths separated by 10 A, a specification derived from target beam-smoothing requirements. Each output from the Q-switched oscillators is phase modulated, amplified, and split in three stages to 48 individual beams plus spares for diagnostic purposes. Finally, each of the 4 X 48 beams is amplitude modulated to a specified temporal pulseshape and is sent via fiber to the preamplifier module (PAM) which is located in the main laser bay next to the large beamlines. The main amplification stages for the Front-End laser are located in the PAM as shown in Fig. 1. A fiber for each beam from the oscillator and modulator subsystem provides the highly formatted 500 pJ pulse to each PAM, where the energy is boosted to 10 mJ in a regenerative amplifier, and then to as much as 10 J in a four-pass flashlamp-pumped rod amplifier. The regenerative amplifier is designed to operate under minimal saturation to preserve the temporal pulse shape, and amplify the pulse by iO with better than pulse to pulse repeatability. A pair of diode-pumped rods was chosen to

Wavefront control of high-power laser beams in the National Ignition Facility (NIF)

SPIE Proceedings, 2000

The use of lasers as the driver for inertial confinement fusion and weapons physics experiments is based on their ability to produce high-energy short pulses in a beam with low divergence. Indeed, the focusability of high quality laser beams far exceeds alternate technologies and is a major factor in the rationale for building high power lasers for such applications. The National Ignition Facility (NIF) is a large, 192-beam, high-power laser facility under construction at the Lawrence Livermore National Laboratory for fusion and weapons physics experiments. Its uncorrected minimum focal spot size is limited by laser system aberrations. The NIF includes a Wavefront Control System to correct these aberrations to yield a focal spot small enough for its applications. Sources of aberrations to be corrected include prompt pump-induced distortions in the laser amplifiers, previous-shot thermal distortions, beam off-axis effects, and gravity, mounting, and coating-induced optic distortions. Aberrations from gas density variations and optic-manufacturing figure errors are also partially corrected. This paper provides an overview of the NIF Wavefront Control System and describes the target spot size performance improvement it affords. It describes provisions made to accommodate the NIF's high fluence (laser beam and flashlamp), large wavefront correction range, wavefront temporal bandwidth, temperature and humidity variations, cleanliness requirements, and exception handling requirements (e.g. wavefront out-of-limits conditions).

Optical system design of the National Ignition Facility

International Optical Design Conference 1998, 1998

Suppresion of Pulsation by Laser Beam Smoothing and Icf With Volume Ignition

Proc. 18th IAEA Fusion …, 2000

A dominating mechanism responsible for the anomalies of the laser-plasma interaction at direct drive laser fusion is the 10 picosecond stochastic pulsation as recognised numerically and experimentally since 1974 and measured in many details by Maddever and Luther-Davies (Australian National University, Canberra) few years ago. These fundamental new results are now in the focus of interest in view of the present difficulties with the big laser-fusion facilities. A drastic reconsideration and economic solution may be possible based on our recent detailed numerical studies which indicate that the stochastic pulsation can be suppressed by an appropriate smoothing of the laser beam, permitting the operation with red light by saving expensive higher harmonic production avoiding damage by UV light, and providing much higher laser energy for fusion. By this way direct drive laser fusion will be favourable using the most robust volume ignition scheme with very high gain.

Four-color beam smoothing irradiation system for laser-plasma interaction experiments at LLNL

1995

A novel four-color beam smoothing scheme with a capability similar to that planned for the proposed National Ignition Facility has been deployed on the Nova laser, and has been successfully used for laser fusion experiments. Wavefront aberrations in high power laser systems produce nonuniformities in the energy distribution of the focal spot that can significantly degrade the coupling of energy into a fusion target, driving various plasma instabilities. The introduction of temporal and spatial incoherence over the face of the beam using techniques such as smoothing by spectral dispersion (SSD) can reduce these variations in the focal irradiance when averaged over a finite time interval. One of the limitations of beam smoothing techniques used to date with solid state laser systems has been the inability to efficiently frequency convert broadband pulses to the third harmonic (351 nm). To obtain high conversion efficiency, we developed a multiple frequency source that is spatially separated into four quadrants, each containing a different central frequency. Each quadrant is independently converted to the third harmonic in a four-segment Type I/Type II KDP crystal array with independent phase-matching for efficient frequency conversion. Up to 2.3 kJ of third harmonic light is generated in a 1 ns pulse, corresponding to up to 65% intrinsic conversion efficiency. SSD is implemented by adding limited frequency modulated bandwidth to each frequency component. This improves smoothing without significant impact on the frequency conversion process. The measured far field irradiance shows 25% rms intensity variation with four colors alone, and is calculated to reach this level within 3 ps. Smoothing by spectral dispersion is implemented during the spatial separation of the FM modulated beams to provide additional smoothing, reaching a 16% rms intensity variation level. Following activation the four-color system was successfully used to probe NIF-like plasmas, producing less than 1% SBS backscatter at greater than 2 multiplied by 1015 W/cm2. This paper discusses the detailed implementation and performance of the segmented four-color system on the Nova laser system.

Two-dimensional beam smoothing by broadband random-phase irradiation

Optics Communications, 1995

A new technique for two-dimensional smoothing is proposed to generate smooth laser irradiation profiles on laser fusion targets employing the broad bandwidth of KrF lasers. In this technique, a wedged etalon is used to get angular dispersion to the orthogonal direction to the one-dimensional broadband random-phase smoothing effect. The preliminary experiment has demonstrated its effectiveness.

Parameter Optimization of 1-D Multi-FM SSD on the NIF (original) (raw)

Related papers