It has been shown that the direct seeding can enhance the performance of a free-electron laser (FEL) in terms of its spectral, temporal, and coherence properties and reduces fluctuations in FEL output energy and arrival-time jitter. The properties of the used seed photon pulse are of high importance. In this paper, we describe the influence of the M² onto the achievable power contrast between the direct seeded and the unseeded FEL radiation. The results of these studies are compared with the data from the high harmonic generation direct seeding experiment ``sFLASH'' in Hamburg, Germany. A method to measure M² from a single transverse intensity distribution of the high harmonics beam at waist is discussed.
No takes yet. Share an insight, caveat, or question.
Ackermann et al. (2013) studied this question.
Synapse has enriched 4 closely related papers on similar clinical questions. Consider them for comparative context: