The ELBE center for high power radiation sources is the largest user facility in the Helmholtz-Zentrum Dresden- Rossendorf. The facility is based on a 36 MeV superconducting RF Linac which can be operated up to 1.6 mA in cw mode. The electron beam is used to generate secondary radiation, such as infrared light (Free Electron Lasers), coherent THz radiation, MeV-Bremsstrahlung, fast neutrons and positrons for a wide range of basic research like semiconductor physics, nuclear astrophysics and radio biological investigations. Two high power laser systems (500 TW Ti:Sa laser, 2 PW diode pumped laser) are under construction for laser acceleration experiments and X-ray generation by Thomson scattering. The FELs are in operation since 2004 (mid-IR FEL, 4-22μm) and 2006 (far-IF FEL, 20-250μm). The fundamental features of the ELBE IR FELs, the FEL instrumentation and advanced beam diagnostics for the photon beam are described. During ten years of user operation experiences and statistical data were collected.
The free-electron laser FELBE at the Helmholtz-Zentrum Dresden Rossendorf enables experiments with spectral,
temporal, and, by means of near-field microscopy, also high spatial resolution. FELBE delivers picosecond IR and THz
pulses in a wavelength range from 4 μm to 280 μm. Here we review the potential of the laser and focus on two highlight
pump-probe experiments. In the first experiment, the relaxation dynamics in self assembled InGaAs quantum dots at
energies below the Reststrahlen band is studied. Long intradot relaxation times (1.5 ns) are found for level separations of
14 meV (3.4 THz), decreasing very strongly to ~ 2 ps at 30 meV (7 THz). The results are in very good agreement with
our microscopic theory of the carrier relaxation process, taking into account polaron decay via acoustic phonons. In the
second experiment, the relaxation dynamics in graphene is investigated at photon energies E = 20 - 250 meV. For
excitations below the energy of the optical phonon (G mode), the relaxation times are more than one order of magnitude
longer as compared to the relaxation times observed for near infrared excitation.