The Aurora Project: Optical Design For A Kilojoule Class KrF Laser

Abstract

IntroductionAurora is a 248-nm,10-kilojoule laser system being built at Los Alamos National Laboratory to demonstrate the feasibility of large KrF laser systems for laser fusion.It was designed as a test bed to demonstrate: 1) efficient energy extraction at 248 nm; 2) an angularly multiplexed optical system that is scaleable to large system designs; 3) the control of parasitics and ASE (amplified spontaneous emission); 4) long path pulse propagation at uv wavelengths; 5) alignment systems for multibeam systems; and 6) new or novel approaches to optical hardware that can lead to cost reduction on large systems.In this paper only issues pertinent to the optical system are addressed.First, a description of the entire system is given. The design constraints on the optical system are explained, concurrent with a discussion of the final design. This is followed by a very brief discussiòn of coatings; in particular, the use of sol -gels for antireflection coatings is presented. System descriptionThe Aurora optical system is designed to match the long, 480 ns amplifier electrical pulse time required for efficient KrF energy extraction to the much shorter, 5 ns optical pulse time required for efficient fusion target interaction.Aurora is designed to demonstrate the critical technologies and to serve as an engineering test bed for megajouleclass laser fusion systems.For the very large megajoule -class lasers, electrical pump times will be in the 300 -500 ns range, and the optical pulse times will be in the 5 -10 ns range.The heart of the Aurora System is the large aperture module (LAM), which has a gain region of 1 m x 1 m x 2 m size. It provides nearly all of the energy and sets many of the system design constraints.The optical system uses angle and time multiplexing to meet the system requirements. The basic building blocks of the system are the following: 1) an oscillator that produces a 5 ns pulse; 2) an optical encoder that replicates the 5 ns pulse 96 times to give 96 separate beams stacked head -to -tail in time producing a 96x5 ns or 480 ns long pulse; 3) an angle encoder and centered optical system that directs each of the beams through the amplifiers, and 4) an optical decoder, which is now being designed, that appropriately delays each of the amplified 5 ns pulses to arrive at the target simultaneously. Figure 1 illustrates the conceptual system design, leaving out the decoder. Figure 2 shows the system layout in the building. Tem2oral encodingThe 5 ns square beam from the oscillator is first divided spatially into right and left halves.One half is delayed by 30 ns with respect to the other.Each half is expanded to about a 15by 23 cm beam. This expanded beam is divided spatially into six parts and each part given a 5 ns delay.The twelve beams resulting from this sequence of aperture division have a total duration of 60 ns and are directed through a two -pass amplifier of 10 by 12 cm aperture.This can be done simply with flat mirrors because the beam size of 7 cm is a good match for the amplifier aperture.After a...

Los Alamos Krypton Fluoride Laser Program

“…The system cost is also influenced by cost of the optical components. Figure 11 shows actual cost experience from the Aurora project in obtaining large uv optics (Hanlon et al 1985). It includes an output window of 62" diagonal dimension.…”

“…It includes an output window of 62" diagonal dimension. A photograph of that piece, for the Aurora system (Rosocha et al 1985) is shown in figure 12.…”