Experiments on semiconductor systems using a pulsed-®eld-magnet free-electron-laser combination C.J.G.M. Langerak a , J. Singleton b, * , L. Li c , L. Van Bockstal c , A. Ardavan b , M.J. van der Pol a , A.F.G. van der Meer a , F. Herlach c , N. Mason b , R.J. Nicholas b , P.J. Walker b a FOM-Institut Rijnhuizen, P.O. Box 1207, NL-3430 Nieuwegein, The Netherlands b Physics Department, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK c VSM, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Heverlee, Belgium Abstract The FELIX free-electron laser is continuously tuneable over the wavelength range 5±100 lm and can provide great power and the possibility of time-resolved experiments in the ns to ls range. We describe a pulsed magnet speci®cally designed for semiconductor experiments using FELIX, which provides ®elds of up to 45 T, with a pulse-shape tailored to the macropulses of the FELIX source. The magnet consists of a conventional outer coil providing ®elds of up to 30 T with a pulse length of several ms, plus a single-layer inner coil with a rise-time of 10 ls, matched to duration of the FELIX macropulses. The magnet is to be extended to ®elds of up to 60 T. Ó 1998 Elsevier Science B.V. All rights reserved. Keywords: Pulsed-®eld magnet; Free-electron laser; Cyclotron resonance; Semiconductor heterostructures The free electron laser FELIX at Rijnhuizen is continuously tuneable over the range 5±100 lm, thus providing a range of (far) infrared wave- lengths normally inaccessible to condensed matter physicists. Alternative sources, such as optically pumped far-infrared lasers and CO 2 lasers, provide only a few discrete wavelengths in this region. At these energies there are many interesting resonant phenomena to be probed in solids, and the best way of studying these is often to tune a character- istic electronic energy such as the cyclotron energy through the resonant region (see e.g. Refs. [1,2]). The eective masses in semiconductor systems im- ply that magnetic ®elds of 10±100 T are required to enable the cyclotron splitting to be probed in the wavelength range of 5±100 lm. The recent combination of FELIX with a 45 T pulsed magnet means that a wide variety of semi- conductor systems can now be studied in the re- gion of interest. The large ®elds available imply that even heterostructure combinations yielding very high carrier densities and/or large spin split- tings such as zero-gap III±V or semimagnetic II± VI systems can be probed deep into the ultraquan- tum limit. The high intensity of the free electron la- ser radiation not only facilitates the detection of the resonances in pulsed ®elds, but also enables non-linear saturation spectroscopy to be used to determine, e.g., electronic lifetimes. The continu- ous tuneability of FELIX oers the possibility of Physica B 256±258 (1998) 339±342 * Corresponding author. Tel.: +44 1865 272236; fax: +44 1865 272400; e-mail: j.singletonl@physics.ox.ac.uk 0921-4526/98/$ ± see front matter Ó 1998 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 8 ) 0 0 5 3 0 - 4