This talk will provide an overview of high power laser research at Lawrence Livermore National Laboratory (LLNL). It will discuss the status of the National Ignition Facility (NIF) laser. In addition, the talk will describe other laser development activities such as the development of high average power lasers and novel fiber lasers.
The National Ignition Facility (NIF) has been in service since 2007 and operating with > 1 MJ energies since 2009. During this time the facility has transitioned to become an international user facility and increased the shot rate from ~150 target shots per year to greater than 400 shots per year. Today, the NIF plays an essential role in the US Stockpile Stewardship Program, providing data under the extreme conditions needed to validate computer models and train the next generation of stockpile stewards. Recent upgrades include the Advanced Radiographic Capability (ARC), a high energy short pulse laser used to do high resolution radiography.
In addition to the NIF, this talk will include an overview of progress on the high average power laser development, recent results from fiber laser development activities and improvements to laser design and computational capabilities.
The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory is the first of a kind megajoule-class laser with 192 beams capable of delivering over 1.8 MJ and 500TW of 351nm light , . It has been commissioned and operated since 2009 to support a wide range of missions including the study of inertial confinement fusion, high energy density physics, material science, and laboratory astrophysics. In order to advance our understanding, and enable short-pulse multi-frame radiographic experiments of dense cores of cold material, the generation of very hard x-rays above 50 keV is necessary. X-rays with such characteristics can be efficiently generated with high intensity laser pulses above 1017 W/cm² . The Advanced Radiographic Capability (ARC)  which is currently being commissioned on the NIF will provide eight, 1 ps to 50 ps, adjustable pulses with up to 1.7 kJ each to create x-ray point sources enabling dynamic, multi-frame x-ray backlighting. This paper will provide an overview of the ARC system and report on the laser performance tests conducted with a stretched-pulse up to the main laser output and their comparison with the results of our laser propagation codes.
At the National Ignition Facility (NIF), home of the world’s largest laser, a critical pulse screening process is used to ensure safe operating conditions for amplifiers and target optics. To achieve this, high speed recording instrumentation up to 34 GHz measures pulse shape characteristics throughout a facility the size of three football fields—which can be a time consuming procedure. As NIF transitions to higher power handling and increased wavelength flexibility, this lengthy and extensive process will need to be performed far more frequently. We have developed an accelerated highthroughput pulse screener that can identify nonconforming pulses across 48 locations using a single, real-time 34-GHz oscilloscope. Energetic pulse shapes from anywhere in the facility are imprinted onto telecom wavelengths, multiplexed, and transported over fiber without distortion. The critical pulse-screening process at high-energy laser facilities can be reduced from several hours just seconds—allowing greater operational efficiency, agility to system modifications, higher power handling, and reduced costs. Typically, the sampling noise from the oscilloscope places a limit on the achievable signal-to-noise ratio of the measurement, particularly when highly shaped and/or short duration pulses are required by target physicists. We have developed a sophisticated signal processing algorithm for this application that is based on orthogonal matching pursuit (OMP). This algorithm, developed for recovering signals in a compressive sensing system, enables high fidelity single shot screening even for low signal-to-noise ratio measurements.
We present the design of a compact UV (263-nm) timing fiducial system for use with x-ray streak cameras at the National Ignition Facility (NIF). The design consists of remote fiber amplification of an infrared 1053-nm (1ω) seed, a free-space optical path that has two stages of frequency conversion from 1ω to the fourth harmonic (4ω), and fiber delivery of the 4ω signal via output fiber for use with an x-ray streak camera. This is all contained within an airbox that can reside in a vacuum. The 1ω seed and the pump light for the fiber amplifier is delivered to the airbox via optical fiber ( 100 meters) from a location in the NIF that is shielded from neutron radiation generated from imploding targets during system shots. When complete, the system will be able to provide timing fiducials to multiple x-ray streak cameras on the same system shot. We will present data that demonstrates end-to-end system performance.*
The National Ignition Facility (NIF) is currently the largest and most energetic laser system in the world. The main
amplifiers are driven by the Injection Laser System comprised of the master oscillators, optical preamplifiers, temporal
pulse shaping and spatial beam formatting elements and injection diagnostics. Starting with two fiber oscillators
separated by up to a few angstroms, the pulse is phase modulated to suppress SBS and enhance spatial smoothing,
amplified, split into 48 individual fibers, and then temporally shaped by an arbitrary waveform generator. Residual
amplitude modulation induced in the preamplifiers from the phase modulation is also pre-compensated in the fiber
portion of the system before it is injected into the 48 pre-amplifier modules (PAMs). Each of the PAMs amplifies the
light from the 1 nJ fiber injection up to the multi-joule level in two stages. Between the two stages the pre-pulse is
suppressed by 60 dB and the beam is spatially formatted to a square aperture with pre-compensation for the nonuniform
gain profile of the main laser. The input sensor package is used to align the output of each PAM to the main laser and
acquire energy, power, and spatial profiles for all shots. The beam transport sections split the beam from each PAM into
four main laser beams (with optical isolation) forming the 192 beams of the NIF. Optical, electrical, and mechanical
design considerations for long term reliability and availability will be discussed. Work performed under the auspices of
the U. S. Department of Energy under contract W-7405-Eng-48.
The National Ignition Facility (NIF) is a high-power, 192-beam laser facility being built at the Lawrence Livermore National Laboratory. The 192 laser beams that will converge on the target at the output of the NIF laser system originate from a low power fiber laser in the Master Oscillator Room (MOR). The MOR is responsible for generating the single pulse that seeds the entire NIF laser system. This single pulse is phase-modulated to add bandwidth, and then amplified and split into 48 separate beam lines all in single-mode polarizing fiber. Before leaving the MOR, each of the 48 output pulses are temporally sculpted into high contrast shapes using Arbitrary Waveform Generators (AWG). Each output pulse is then carried by optical fiber to the Preamplifier Module (PAM) where it is amplified to the multi-joule level using a diode-pumped regenerative amplifier and a multi-pass, flashlamp-pumped rod amplifier. Inside the PAM, the beam is spatially shaped to pre-compensate for the spatial gain profile in the main laser amplifiers. The output from the PAM is sampled by a diagnostic package called the Input Sensor Package (ISP) and then split into four beams in the Preamplifier Beam Transport System (PABTS). Each of these four beams is injected into one of NIF's 192 beam lines. The combination of the MOR, PAM, ISP and PABTS constitute the Injection Laser System (ILS) for NIF. This system has proven its flexibility of providing a wide variety of pulse shapes and energies during the first experiments utilizing four beam lines of NIF.
The detection and temporal dispersion of the x rays using x ray streak cameras has been limited to a resolution of 2 ps, primarily due to the transit time dispersion of the electrons between the photocathode and the acceleration grid. The transit time spread of the electrons traveling from the photocathode to the acceleration grid is inversely proportional to the accelerating field. By increasing the field by a factor of 7, we have minimized the effects of transit time dispersion in the photocathode/accelerating grid region and produce an x-ray streak camera with sub-picosecond temporal resolution (approximately equals 900 fs). The streak camera has been calibrated using a Michelson interferometer and 100 fs, 400 nm laser light. Time resolved x-ray data is shown from an aluminum target heated at 1018 W/cm2 with a 100 fs, 400 nm laser.
We have developed a moveable, multi-anode, electron-induced x-ray source for calibrating x-ray imaging detector systems. The source features four water-cooled, copper-based anodes that are easily replaced and interchangeable under vacuum. A spherically symmetric filament and anode configuration yields very symmetrical source spot sizes variable from 1 to 5 mm diam. The source is coupled to vacuum by means of a triple-axis translator with x and z motions computer controlled to better than +/- 13 micrometers step accuracy. Absolute source flux is continuously monitored with a proportional counter. We characterize the source spot in detail by aiming the anode towards a pin-hole imaging x-ray detector system. To date we have used Co, Fe, Mg, and Ge vapor-deposited on copper anodes. When filtered with Ni or Mg foils, these emitting materials provide sets of four moderately pure x-ray lines below 1.5 keV. High deposition purity as well as 1E-7 torr source chamber pressures help reduce source degradation. Source translation and data acquisition are computer controlled using a Macintosh/LabVIEW software system. We discuss the application of our source configuration to spatial calibrations of extended pinhole and slit imaging detector systems. In addition, our multi-anode capability is useful for calibrating x-ray spectrograph response versus wavelength.
We have designed and built an x-ray streak camera with subpicosecond time resolution. This camera attains its fast temporal resolution through a very strong extraction field, 100,000 V/cm, at the photocathode. It incorporates a narrow electron emission band photocathode that will also help the time resolution. The total time resolution has been calculated to be near 600 fs.