OMEGA, a 60-beam, 351 nm, Nd:glass laser with an on-target energy capability of more than 40 kJ, is a flexible facility that can be used for both direct- and indirect-drive targets and is designed to ultimately achieve irradiation uniformity of 1% on direct-drive capsules with shaped laser pulses (dynamic range ≳400:1). The OMEGA program for the next five years includes plasma physics experiments to investigate laser–matter interaction physics at temperatures, densities, and scale lengths approaching those of direct-drive capsules designed for the 1.8 MJ National Ignition Facility (NIF); experiments to characterize and mitigate the deleterious effects of hydrodynamic instabilities; and implosion experiments with capsules that are hydrodynamically equivalent to high-gain, direct-drive capsules. Details are presented of the OMEGA direct-drive experimental program and initial data from direct-drive implosion experiments that have achieved the highest thermonuclear yield (1014 DT neutrons) and yield efficiency (1% of scientific breakeven) ever attained in laser-fusion experiments.

A model SiO2 thin-film system containing gold nanoparticles serving as nanoscale absorbing defects is investigated with the goal of unraveling the connection between the 351 nm pulsed-laser energy absorption process inside a single defect and the resulting film damage morphology. For this purpose, gold nanoparticles are lodged at a well-defined depth inside a SiO2 monolayer film. Particle sites, as well as nanoscale craters generated at these locations after 351 nm irradiation, are mapped by means of atomic force microscopy. The results of this mapping confirm a damage mechanism that involves initiation in the nanoscale defect followed by absorption spreading out to the surrounding matrix. At low laser fluences (below optically detected damage onset), the probability of crater formation and the amount of the material vaporized is, to within ±25% of the average value, almost independent of the particle size. Inhomogeneities in the particle environment are held responsible for variances in the laser-energy absorption process and, consequently, for the observed particle/crater correlation behavior. Investigation of the damage threshold as a function of particle size (2–19 nm range) showed that even few-nanometer-diameter particles can lead to a significant threshold reduction. The “nanoscale” damage threshold is introduced as a laser fluence causing localized melting without significant vaporization.

Hafnium oxide thin films with varying oxygen content were investigated with the goal of finding the optical signature of oxygen vacancies in the film structure. It was found that a reduction of oxygen content in the film leads to changes in both, structural and optical characteristics. Optical absorption spectroscopy, using nanoKelvin calorimetry, revealed an enhanced absorption in the near-ultraviolet (near-UV) and visible wavelength ranges for films with reduced oxygen content, which was attributed to mid-gap electronic states of oxygen vacancies. Absorption in the near-infrared was found to originate from structural defects other than oxygen vacancy. Luminescence generated by continuous-wave 355-nm laser excitation in e-beam films showed significant changes in the spectral profile with oxygen reduction and new band formation linked to oxygen vacancies. The luminescence from oxygen-vacancy states was found to have microsecond-scale lifetimes when compared with nanosecond-scale lifetimes of luminescence attributed to other structural film defects. Laser-damage testing using ultraviolet nanosecond and infrared femtosecond pulses showed a reduction of the damage threshold with increasing number of oxygen vacancies in hafnium oxide films.