TUOAI02
ANL, Argonne, USA
SLAC, Menlo Park, California, USA
TISNCM, Troitsk, Russia
LBNL, Berkeley, California, USA
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
The Linac Coherent Light Source (LCLS) has produced extremely bright hard x-ray pulses using self-amplified spontaneous emission (SASE) since 2009. In SASE, the electron beam shot noise initiates the FEL gain, resulting in output radiation characterized by poor temporal coherence and a fluctuating spectrum whose normalized width is given by the FEL bandwidth. Recently, colleagues at DESY suggested a self-seeding scheme for the LCLS to reduce the bandwidth*. Here, the SASE produced in the first half of the undulator line is put through a simple diamond-based monochromator; the resulting monochromatic light trailing the main SASE pulse is used to seed the FEL interaction in the downstream undulators. We report on the experimental results implementing such a scheme at the LCLS, in which we have measured a reduction in bandwidth by a factor of 40-50 from that of SASE at 8-9 keV. The self-seeded FEL operates close to saturation, with the maximum output energy approximately equal to that with no seeding for low charge. The observed level of power fluctuations in the seeded output is presently rather large, and future plans focus on discovering their origins and reducing their magnitude.
* Geloni, V. Kocharyan ,and E.L. Saldin, DESY 10-133, arXiv:1008.3036 (2010)
THOAI01
LBNL, Berkeley, California, USA
SLAC, Menlo Park, California, USA
Current and planned X-ray FELs produce pulses with sub-10fs duration, requiring comparable timing stability to enable pump/probe experiments. We describe methods of achieving stability on this time scale, for FEL facilities hundreds of meters long. Our approach is based on CW and amplitude modulated optical signals delivered over fiber to pulsed lasers. A comprehensive design approach includes control of modelocked laser oscillators, amplifiers, propagation paths, arrival time diagnostics and finally cross-correlation between pump and probe signals at the experiment. Design options depend on global FEL parameters such as repetition rate. We show that current laser technology is capable of supporting performance at the few-femtosecond level using these techniques. High precision is achieved by leveraging recently developed, frequency stable spectroscopic lasers and optical clocks, as well as the mature field of fiber interferometry. Current experimental results using pulsed and CW lasers are described.
DESY, Hamburg, Germany
SLAC, Menlo Park, California, USA