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Surfaces, Microstructure and Fracture Group

We have an experimental laser-launched flyer system.  This consists of a Q-switched Nd:YAG laser with a half-joule pulse energy, and an array of optics to condition, analyse and focus the beam.  The focussed pulse falls on a film, a few microns thick and supported by a transparent substrate.  The area irradiated is of order a square millimetre.  The high energy density in this region converts a thin layer of the film to plasma, driving the remaining thickness forward at speeds of a few kilometres per second. 

There are two main strands of research using the laser-launched flyer system.  The first is improvement of the system itself, studying beam conditioning and flyer design to optimize flyer speed and shape.  The main recent innovations in this field have been a spatial filter system, and the development of layered flyers.  The latter are based on the observation that the mechanical properties required for a good flyer, and the optical and thermal properties required for efficient plasma generation, may not occur in the same material.  By forming an "ablation layer" between the incident light and the flyer itself, both requirements can be met. 

The second strand consists of characterizing the response of energetic materials to shocks of nanosecond duration and tens of gigapascal magnitude.  Using a hundred-micron standoff the flyer is given space to form before striking the material's surface, but the impact takes place early enough that oxidization does not destroy the flyer.  Given efficient coupling between the flyer and the explosive, this system holds out the promise of providing excellent timing control for detonation, and eliminating potentially hazardous primary explosives from explosive systems.