National Ignition Facility wavefront requirements and optical architecture

Abstract

With the first four of its eventual 192 beams now executing shots and generating more than 100 kJ of laser energy at its primary wavelength of 1.06 µm, the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory is already the world's largest and most energetic laser. The optical system performance requirements that are in place for NIF are derived from the goals of the missions it is designed to serve. These missions include inertial confinement fusion (ICF) research and the study of matter at extreme energy densities and pressures. These mission requirements have led to a design strategy for achieving high-quality focusable energy and power from the laser and to specifications on optics that are important for an ICF laser. The design of NIF utilizes a multipass architecture with a single large amplifier type that provides high gain, high extraction efficiency, and high packing density. We have taken a systems engineering approach to the practical implementation of this design that specifies the wavefront parameters of individual optics to achieve the desired cumulative performance of the laser beamline. This paper provides a detailed look at the causes and effects of performance degradation in large laser systems and how NIF has been designed to overcome these effects. We also present results of spot size performance measurements that have validated many of the early design decisions that have been incorporated in the NIF laser architecture.