Properties of the ultrashort gain length, self-amplified spontaneous emission free-electron laser in the linear regime and saturation

The Next Generation of X-ray Sources

We discuss recent results on soft and hard X-ray free electron lasers (FELs) and how they can be used to design and optimize the next generation of these sources of high brightness, coherent photons, with femtosecond pulse duration, or very narrow linewidth. In particular, we consider the experimental and theoretical progress in the electron beam generation and manipulation. These results, when combined with the successful development of powerful simulation codes, can be used to design optimized, high intensity sources of coherent photons, and to reduce their size and cost.

Observation of anomalously large spectral bandwidth in a high-gain self-amplified spontaneous emission free-electron laser

Observation of ultrawide bandwidth, up to 15% full-width, high-gain operation of a self-amplified spontaneous emission free-election laser (SASE FEL) is reported. This type of lasing is obtained with a strongly chirped beam (deltaE/E approximately 1.7%) emitted from the accelerator. Because of nonlinear pulse compression during transport, a short, high current bunch with strong mismatch errors is injected into the undulator, giving high FEL gain. Start-to-end simulations reproduce key features of the measurements and provide insight into mechanisms, such as angular spread in emitted photon and electron trajectory distributions, which yield novel features in the radiation spectrum.