ISSUES IN HIGH HARMONIC SEEDING OF THE 4GLS XUV-FEL

Using High Harmonics (HH) as a seed for free electron lasers is currently under consideration in a number of proposed facilities. An HH seed source is independent of machine dynamics, and allows for extensive manipulation of the seed pulse using well-established techniques of ultrafast laser physics. These allow for rapid tuning, and may enable the extension of chirped pulse amplification and even pulse shaping for coherent control to short wavelengths. In addition, there are advantages in terms of noise and synchronization. There are a number of issues involved in the implementation of HH seeding: energy, tunability, coherence, temporal structure, etc. We discuss these issues and their application in the 4GLS XUV-FEL