Optical Surfaces has supplied two ultra-high precision mirrors to the Atomic Weapons Establishment to help upgrade the performance of the Helen terrawatt laser facility
In the post nuclear test ban treaty era, the Atomic Weapons Establishment (AWE)'s Helen laser has enabled simulation of the key physics processes occurring within a thermonuclear weapon.
AWE's scientists have carried out pioneering warhead physics work taking advantage of the laser's short pulse times and precise targeting.
As a result AWE has been able to study the individual phenomena occurring within a warhead in order to validate the computer generated predictions.
By converting one of the Helen beams to sub-picosecond pulse operation using the chirped pulse amplification technique, AWE recently achieved 100 terrawatt output.
To make best use of this enhanced power the highest quality achievable off-axis parabolic focusing mirror was required to maximise beam intensity while keeping the target outside the beam aperture.
Optical Surfaces was selected as the supplier for these mirrors due to its technical excellence, reasonable pricing and a proven record in manufacturing and testing large high precision optics for leading plasma physics groups around the world, it says.
To provide the precise beam focusing required by the Helen laser placed great demands on the quality of the optical components.
These were two 270mm diameter off-axis paraboloids of 600mm focal length having a steep off-axis angle to the edge of 27deg, resulting in an asphericity of 500 microns.
Based upon proprietary, flexible lapping technology and its uniquely stabilised environment, Optical Surfaces says it was able to produce superbly smooth optics of lambda/10 surface accuracy with slope errors of less than lambda/10 per centimetre.
A particular problem with generating this type of aspheric is not only the high slope departures from spherical, but also the extreme variation of those departures from one side of the mirror to the other.
