Description
25 years after the first lasing of FLASH and 20 years of operation as a user facility, delivering free electron laser radiation in EUV and soft X-ray spectral range, the source underwent a massive refurbishment and upgrade project under the umbrella of the FLASH2020+ project. This included the modification of the FLASH1 beamline to deliver seeded free electron laser (FEL) pulses for users.
Externally seeded FELs are powerful sources of laser-like radiation with high transverse and longitudinal coherence. In contrast with self-amplified spontaneous sources (SASE), where the radiation fluctuates on shot-to-shot basis due to their start-up from noise, seeded FELs provide stable and reproducible pulses at the Fourier limit for Users' experiments in non-linear science.
The FLASH upgrade is achieved by combining high gain harmonic generation and echo-enabled harmonic generation with a wide-range wavelength-tunable seed laser, to efficiently cover the 60-4 nm wavelength range. The undulator chain has been refurbished entirely using new radiators based on the APPLE- III design, allowing for polarization control. By leveraging the FLASH superconducting linac to deliver electron beams at MHz repetition rates in burst mode, and pairing it with newly developed, synchronized laser systems, the facility is now uniquely positioned to provide the User community with high-repetition-rate, seeded FEL radiation to push the boundaries of modern photon science.
