Statistical properties of the radiation from VUV FEL at DESY operating at 30 nm wavelength in the femtosecond regime

Since spring, 2005 vacuum ultraviolet free electron laser (VUV FEL) at DESY operates as user facility in the wavelength range around 30 nm. Electron beam formation system at the VUV FEL is essentially nonlinear and naturally results in a formation of a short high-current leading peak in the density distribution that produces FEL radiation. The main feature of the femtosecond mode of operation of the VUV FEL is the production of short, down to 20 fs radiation pulses with GW-level peak power. This paper is devoted to detailed studies of the short-pulse effects in the VUV FEL at DESY operating in the femtosecond regime, and to analysis of first experimental results