Free-Electron Lasers (FELs) are light sources offering highly brilliant, low-bandwidth radiation pulses with a widely tunable wavelength in the IR, visible or XUV to X-ray range. The FEL FLASH operates between 4.1 and 45nm. Typically photon pulses between 50 and 200fs (FWHM) are generated.
Many users at FLASH work on pump-probe experiments, where time resolution is limited by the pulse duration. Therefore they have expressed a keen interest in being provided with shorter XUV pulses.
The shortest possible pulse is a single longitudinal optical mode of the FEL radiation. This “single spike radiation” can be produced using very short electron bunches of only a few femtoseconds bunch duration.
Due to limitations of the bunch compression low bunch charges and shorter electron bunches exiting the photo-injector are required. Therefore, a new short-pulse injector laser with adjustable pulse duration in the range of 1.7ps to 4ps FWHM and bunch charges up to 200pC was installed at FLASH to optimize the bunch parameters before compression in magnetic chicanes.
Beam dynamic studies show that single mode radiation can indeed be achieved at FLASH by this approach.
This talk covers start-to-end simulation, improvements of diagnostics to adapt for charges and bunch lengths that are very small compared to standard FLASH operation, and first experimental results.