The Free Electron Laser

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Professor CR Pidgeon

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 CRP directs an active programme on nonlinear and time-resolved semiconductor spectroscopy at FELIX. The emphasis is on electron and spin lifetime design and device optimisation by band structure engineering.

Our present programme emphasises 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. In the first case the ultimate object is to produce a spin FET device from narrow gap semiconductor components where electron spin is modulated by a gate electrode by contrast with electron charge in conventional FETs. In the second case we are doing the investigation required through optically pumped Si/SiGe quantum cascade (QC) structures to ultimately produce an electrically pumped Si/SiGe quantum cascade laser.

The Dutch Free Electron Laser (FELIX) at Utrecht