Status and perspectives of single pass free electron lasers for short wavelengths

Abstract
First lasing of a single-pass free electron laser below 100 nm wavelength was recently observed at the TESLA Test Facility at DESY, after a singular experiment with very high gain at Los Alamos National Laboratory at 12 µm wavelength in 1997 and a very recent expriment at 530 nm at Argonne National Laboratory. These novel devices are based on the principle of self-amplified spontaneous emission (SASE), allowing very high gain up to saturation in a single pass through a long periodic magnetic structure. This concept does not require any optical components and promises to produce intense, sub-picosecond laser pulses for a very wide, continuous range of wavelengths down to approximately 0.1 nm. The experimental results at DESY and the other laboratories are in agreement with theory and indicate that SASE FELs will soon be available for experiments in the VUV and soft X-ray region. This paper gives an overview of the status of the present SASE projects and the anticipated research and development in the near future. It focuses particularly on the recent results at DESY and the current program towards a VUV user facility.