Simulation of the short-pulse effects in high-gain FELs starting from noise

With one-dimensional time-dependent FEL equations, we have numerically investigated the spatio-temporal evolution of high-gain free-electron lasers starting from noise. Considering the effects of slippage, electron density profile, and the electron-beam energy spread, we describe the general features of the short-pulse SASE-FEL. Throughout the extensive simulation calculation, the scaling laws for the short-pulse SASE are presented for the prediction of the SASE performance in all wavelength regions.