We discuss several experiments that can be carried out at BNL's DUVFEL to address several issues associated with cascaded HGHG FELs. These include: Chirped Pulse Amplification (CPA); HGHG with seed shorter than electron bunch length; 8^th harmonic HGHG (from 800nm to 100nm); Regenerative synchronization of seed pulse and electron bunch; Tuning of HGHG without changing seed, proposed by Timur Shaftan; Cascading using NISUS and VISA: from 400nm to 100nm to 50nm. These experiments may have important impact on the development of multi-stage cascaded HGHG FELs.

First lasing of the mid infrared FEL at ELBE was achieved on May 7, 2004. The Radiation Source ELBE at the Forschungszentrum Rossendorf in Dresden is currently under transition from commissioning to regular user operation. Presently the electron linac produces an up to 18 MeV, 1 mA (cw) electron beam which is alotted to generate various kinds of secondary radiation. After the successful commissioning of the bremsstrahlung and channeling-X-ray facilities during 2003 stable lasing has now been observed in the IR range (15 to 22 μm). The oscillator FEL is equipped with two planar undulator units, both consisting of 34 hybrid permanent magnet periods of 27.3 mm (K_rms = 0.3 - 0.8). The distance between the two parts is variable and the gaps can be adjusted and tapered independently. At 19.6 µm an optical power of 3W was out-coupled in a macro pulse of 0.6 ms duration using an electron beam energy of 16.1 MeV and an energy spread of less than 100 keV; the micropulse charge was 50 pC and its width slightly above 1ps. With the installation of a second acceleration module for additional 20 MeV smaller wavelengths will become available in the near future.