Free electron lasers (FELs) represent a radical alternative to conventional lasers, being potentially the most flexible, high power and efficient generators of tunable coherent radiation from the ultra-violet to the infrared. A FEL does not have the restrictions of conventional lasers on operating wavelengths, and is constrained only by the phase-matching condition for strong interactions between the electrons and laser field - i.e. for a given periodic magnet (wiggler) structure, the wavelength is determined only by the energy of the electron beam. The FEL has come of age and there are now ‘user facilities' in Europe and America. CRP (together with Professor B N Murdin, University of Surrey) is in charge of the EPSRC funded UK ‘user station' at the Dutch FEL (FELIX) and directs an active programme on nonlinear and time-resolved (electron orbital and spin) semiconductor spectroscopy. The emphasis has been on electron and spin lifetime design and device optimisation by band structure engineering. Our programme has emphasised two research themes in semiconductor device physics: electron spin relaxation and spin injection studies of narrow gap semiconductor structures; and optically pumped Si/SiGe quantum fountain and impurity lasers. Most recently we have embarked on a joint research programme between the universities of Surrey (Murdin), UCL (Aeppli) and Heriot-Watt (Pidgeon) on coherent control of Rydberg states in silicon, pumped near 30µm with FELIX in multi-beam pump-probe configurations.

Carl Pidgeon is professor of semiconductor physics at Heriot Watt University. He is a Fellow of the Royal Society of Edinburgh and the Institute of Physics. In 1995 he became Coordinator of the EPSRC/FOM laser science programme at the Dutch Free Electron Laser (FEL - acronym FELIX), as well as continuing to be leader of the consortium and principal investigator of the UK semiconductor physics programme at FELIX.  On his retirement in 2003 he passed on this role to B N Murdin, with whom he actively collaborates.