John A. Hanlon

Aurora multikilojoule KrF laser system prototype for inertial confinement fusion

Aurora is the Los Alamos National Laboratory short-pulse, high-power, KrF laser system. It serves as an end-to-end technology demonstration for large-scale ultraviolet laser systems of interest for short wavelength, inertial confinement fusion (ICF) investigations. The systems is a prototype for using optical angular multiplexing and serial amplification by large electron-beam-driven KrF laser amplifiers to deliver stacked, 248-nm, 5-ns duration multikilojoule laser pulses to ICF targets using an --1-km-long optical beam path. The entire Aurora KrF laser system is described and the design features of the following major system components are summarized: front-end lasers, amplifier train, multiplexer, optical relay train, demultiplexer, target irradiation apparatus, and alignment and controls systems.

The Aurora Laser Optical System

The Los Alamos National Laboratory KrF Aurora laser optical system is described. Conceptual, first-order, and detailed designs are presented for the major 248-nm ultraviolet optical, subsystems. In Aurora, a 5-ns front-end pulse is replicated and time encoded into a 96-beam, 480-ns pulse train, angle encoded, amplified, and then time and angle decoded so that all the 5-ns pulses arrive at the target plane simultaneously. The encoder and the centered optical system that directs the pulse train through the amplifiers have been installed, on major alignment system has been built and tested, and most decoder optical components have been designed and ordered. The plan is to have the entire optical system installed and initial integration completed by October 1987.

Beam Propagation Considerations in the Aurora Laser System

Aurora is a high-power KrF laser system now being constructed for inertial confinement fusion (ICF) studies. It will use optical angular multiplexing and serial amplification by electron-beam-driven KrF amplifiers to deliver a stacked, multikilojoule 5-ns-duration laser pulse to ICF targets. The requirements of angular multiplexing KrF lasers at the multikilojoule level dictate path lengths on the order of 1 km. The inherent complicated path crossings produced by angular multiplexing and pulse stacking do not allow isolation of individual beam lines, so the optical quality of the long beam paths must be controlled. Propagation of the 248-nm light beams over long paths in air is affected by scattering, absorption thermal gradients and turbulence, beam alignment, and control and optical component figure errors.

Helios Target Positioning System

The Los Alamos Scientific Laboratory Helios laser fusion system focuses eight powerful CO2 laser beams onto a tiny (typical 300-μm-diam) DT-filled target. The focusing is accomplished inside a vacuum chamber that is 3.5 m in diameter by 3.5 m high. The target positioning system places the target to within 5.0 μm of a predetermined point in space. This is accomplished by using two orthogonal autocollimating telescopes to determine the center of a precisely located surrogate sphere. The target is then placed at the common focal point of the two telescopes. The Helios target positioning system has been meeting or exceeding its design requirements for about one year with minimal maintenance. It has proven to be a very effective system.

Aurora: multi‐Kilojoule KrF laser system for ICF studies

Aurora is a high power KγF laser system used to deliver multi‐kilojoule 5ns 248‐nm laser pulses to fusion targets. System specification are described.