Generation of ultra-short low-charge electron bunches for single-spike SASE radiation at the Free-Electron Laser in Hamburg

Dissertation, Universität Hamburg, 2017; 144 pp. (2018). = Dissertation, Universität Hamburg, 2017
High-gain Free-Electron Lasers (FEL) constitute a powerful source of intense, short radiation pulses in the XUV and X-ray range that are used in a wide variety of research fields. They typically work in the Self-Amplified Spontaneous Emission (SASE) Mode. As a consequence of the statistical nature of this process, the radiation pulses exhibit a low degree of longitudinal coherence. There are basically two approaches for improving the longitudinal coherence. First, the so-called seeding of the FEL process, where the FEL radiation properties are controlled by a coherent seed-pulse coupled into the beam line. Second, the generation of very short FEL pulses that contain only a single longitudinal mode of the radiation. This thesis deals with the latter method and with the attempt to establish it at the Free-Electron Laser in Hamburg (FLASH), in order to offer photon pulses to the users that transversely as well as longitudinally exhibit a high degree of coherence.For this purpose, analytical and numerical studies were performed to determine the required parameters of the accelerator (essentially bunch length, a modification of the photo-injector laser). These parameters have been successfully realized at FLASH and first measurements of the generated FEL pulses have been conducted. It could be verified that the photon pulses indeed contain little more than a single coherent mode in average.