1. School of Computer Science and Electronic Engineering, Bangor University, Dean Street, Bangor, Gwynedd LL57 1UT, United Kingdom
2. James Watt School of Engineering, University of Glasgow, Glasgow G12 8QQ, United Kingdom
3. Ultra Precision Structured Surfaces Ltd, OpTIC Centre, Ffordd William Morgan, St Asaph Business Park, St Asaph, Denbighshire LL17 0JD, United Kingdom