Broadband spectrally incoherent pulses are a possible strategy to mitigate the laser–plasma instabilities and beam imprint that detrimentally impact the coupling of high-energy laser pulses into targets. The Laboratory for Laser Energetics is building a laser facility, the Fourth-generation Laser for Ultrabroadband eXperiments (FLUX), that will deliver UV pulses with sufficient bandwidth and energy to perform relevant experiments with the 60 narrowband OMEGA beams. The supporting laser technologies, laser design, and status will be presented.

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory contains a 192-beam 4.2 MJ neodymium glass laser (around 1053 nm or 1w) that is frequency converted to 351nm light or 3w. It was built to access the extreme high energy density conditions needed to support the nation’s nuclear stockpile in the absence of further underground nuclear tests, including studying Inertial Confinement Fusion (ICF) and ignition in the laboratory. Over the last year, important results have been obtained demonstrated a fusion yield of 1.35MJ with 1.9MJ of laser energy (and 440 TW power) injected in the target, bringing the NIF to the threshold of ignition [2-3]. As the yield curve near ignition is steep, the laser performance team has focused on providing improved power accuracy and precision (better shot-to-shot reproducibility) with a high-fidelity pulse shaping system (HiFiPS), and also on extending the NIF operating power and energy space by 15% to 2.2MJ and 500TW.

The National Ignition Facility (NIF) is a 192-beam laser operated as an experimental facility to support its science-based stockpile stewardship program. The facility delivers up to 1.9 MJ UV energy to targets creating temperatures and pressures only found at the center of stars. The facility routinely conducts experiments supporting inertial confinement fusion, high energy density stockpile science, national security applications, and fundamental science. In this talk we will review how complex high energy density experiments are planned and performed in the world’s largest laser facility including configuring and aligning the lasers, the target experimental systems and the diagnostics. We will show the measures we take to safely conduct experiments that create extreme neutron fluxes. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344-ABS-LLNL-ABS-815547

Polarization smoothing of the 3w beam is highly desirable for direct-drive inertial confinement fusion experiments. However, fabrication methods of large-aperture optics that provide “randomized” beam polarization on the target are limited in-part to the challenging nature of the optical materials with suitable birefringence values. We report on the development of two new polarization-smoothing optics by separate and distinctly different approaches. In the first approach, a nematic liquid crystal with a high laser-induced–damage threshold is aligned between two fused silica substrates, with one substrate possessing a freeform, contoured imprint. In the second approach, freeform surface imprinting of potassium dihydrogen phosphate crystals is accomplished by fluid jet polishing.

Direct-drive fusion implosion experiments using the 60-beam OMEGA Laser System require ~1% rms uniformity on target. To fully characterize on-target uniformity, a full-beam in-tank diagnostic that measures the on-shot, full-energy focal spot of 28 of the 60 beams inside the target chamber was deployed in 2018. While this diagnostic demonstrated the absence of gross nonuniformities, questions about lower-level variations and their effects on overall uniformity remained. We will present improvements in dynamic range, a new wavefront measurement capability, a summary of the 28 beams characterized to date, and a discussion of observed differences between beams under varying shot conditions.

In this work, we demonstrate an improved approach to power balancing the OMEGA Laser System that can target a 200-ps temporal feature in a given pulse shape. This optimization is achieved while maintaining the average power balance over the entire pulse shape. To accomplish this, a 60-beam power balance model of the OMEGA Laser System has been developed that uses measured losses and gains at each amplification stage on the system as inputs. The model is used to adjust the gain on the appropriate saturated amplifier to compensate for known losses on the system.

Current state-of-the art radiation-hydrodynamic codes do not include the physics involved in the laser-induced solid-to-plasma transition. However, this transition process is understood to significantly impact the resulting ablation and shock front geometry, due to “laser imprint” and “shinethrough.” An experimental system involving synchronized femtosecond and picosecond lasers is developed to initiate and characterize dynamics of planar target materials irradiated by conditions similar to a “picket” prepulse from a direct-drive pulse shape. Ultrafast imaging of the resulting plasma formation, plume expansion, and shock-wave propagation is performed with femtosecond-scale resolution for a polystyrene target. These results may be used to improve future direct-drive experimental and modeling efforts.

The University of Rochester’s Laboratory for Laser Energetics (LLE) and Institute of Optics provide comprehensive educational opportunities in lasers and optics that support research in inertial confinement fusion (ICF). Undergraduate and graduate students take courses in optical system design, coatings, and ultrafast and petawatt laser systems and pursue ICF-relevant research topics such as bandwidth enhancement of high-average power lasers, cryogenic cooling of diode-pumped materials, and UV photodiode-based characterization of OMEGA 60 pulses. Supporting future workforce needs, LLE has pioneered high-school programs that 1) invite students to participate in ICF-related research and 2) introduce ICF science to students from underrepresented minorities.