Radiation Pulse Compression for a SASE-FEL

The total radiation pulse consists of NS spikes, and the total pulse length is LP=NSLc. In a normal configuration all the spikes have the same line-width and the same central frequency. Chirping the pulse, i.e. changing the frequency of each spike by a quantity proportional to the spike longitudinal position inside the pulse, allow us to compress the pulse using a pair of diffraction gratings. The pulse length can then be changed between NSLc and Lc. In the case of an X-ray SASE-FEL like LCLS [2] with about 250 spikes in a pulse, this would allow us to change the X-ray pulse length, in an ideal case, from about 230 fs to the length of one spike. The system peak power would thus be increased by a factor of more than 100 to the Terawatt level, while the intensity fluctuations and the line width remain unchanged. Since the radiation wavelength depends on the beam energy as