Laser ablated surface engineering: from discovery to machine application

In the past few years we have established that Laser Ablation Surface Engineering (LASE) is a very effective way of producing surfaces which have Secondary Electron yields (SEY) < 1. These can be achieved with a variety of laser pulse durations from nano- to pico seconds. Unfortunately the features (i.e. moderately deep grooves and nano-particulates) that help to reduce the SEY also produce undesirable effects such as an increase in surface impedance and loose particulates. In this paper we have examined several techniques to minimise these unwanted effects. For reducing the depth of the surface altered layer femtosecond laser pulses are used which generate wave- length-scale surface structures with directionality and periodicity, known as laser-induced periodic surface structure (LIPSS). The reduction in SEY in most cases has been less effective, but a few laser processing parameters have produced reasonable SEY values (less than 1 for primary electron energy below 400 eV). The role of processing atmosphere has also been examined where the processing in inert gas (Ar) resulted in a non-stoichiometric oxide surface as compared with air laser treated surfaces that resulted in fully oxidised state. The latter inhibited the growth of carbon on the surface but still aged with time and yielded a higher SEY after sever- al months of exposure to air.