One of the critical aspects of a successful laser experiment is the design and manufacture of the target. This is the role of the Target Fabrication section, which has provided all of the miniature targets for the HELEN laser programme over the last 27 years and many more for collaborative experiments using US facilities.
A HELEN target is generally comparable in size to a single grain of sugar. Each target usually contains several sub-components which are, of course, much smaller still. These sub-components often require coatings of material that can be as thin as a few nanometres thickness – only 10’s of atoms deep!
The target designs proposed by experimentalists often require long development programmes to be able to manufacture the targets. These can range from making foams with specific dopants, to being able to sputter coat solid density metal layers or to being able to machine very low density foams. This last requirement has led to the development of a laser-based micro-machining laboratory.
Target manufacture is only half of the issue - experimentalists need to know how closely the final target met the design specification. To achieve this, considerable effort is spent on target metrology. Several different techniques, such as radiography, scanning-electron microscopy (SEM), white-light interferometry and atomic-force microscopy (AFM), are used to obtain the information.