[1] Heriot Watt Univ, SUPA, Inst Photon & Quantum Sci, Edinburgh EH14 4AS, Midlothian, Scotland
[2] Univ Glasgow, Sch Engn, Glasgow G12 8LT, Lanark, Scotland
[3] Purdue Univ, Sch Elect & Comp Engn, 1205 West State St, W Lafayette, IN 47907 USA
[4] Purdue Univ, Birck Nanotechnol Ctr, 1205 West State St, W Lafayette, IN 47907 USA
[5] Univ St Andrews, Sch Phys & Astron, SUPA, St Andrews KY16 9SS, Fife, Scotland