FLASH (Free Electron Laser in Hamburg), is the world’s first FEL designed and constructed for the extended ultraviolet and soft X-ray spectral range (XUV) by the Deutsches Elektronen-Synchrotron (DESY) in Hamburg, Germany. This facility has provided extremely bright, coherent and ultra short XUV pulses for a broad science programme conducted by scientists from all over the world since 2005. FLASH has also served as a pilot facility for the European XFEL which has been under construction in Hamburg since 2009 and is based on the same accelerator technology.
More information on the FLASH machine and the FLASH photon beamlines and user operation can be found on our websites.

FLASH is a high-gain FEL which achieves laser amplification and saturation in a single pass of a relativistic electron packet through a magnetic structure called undulator. The electron bunches are produced in a short-pulse laser-driven photo injector and accelerated by a superconducting linear accelerator. The superconducting technique allows to accelerate thousands of bunches per second which is not possible with other technologies. The lasing process is initiated by spontaneous radiation in the undulator, and brought to saturation by the self-amplified spontaneous emission (SASE) process. Femtosecond coherent light pulses emerge from the 30 m long undulator in the accelerator tunnel and can be delivered alternatively to five experimental stations in the FLASH experimental hall by a photon beam transport system operating under ultra-high vacuum conditions.

FLASH covers a wavelength range of approximately 4 - 45 nm with pulse energies up to ~500 µJ and pulse durations between <50 fs and 200 fs. In addition, a planar electromagnetic undulator with ten periods just behind the SASE undulator can be used to create strong, coherent THz radiation pulses with pulse energies of ~100 μJ which are strictly synchronous with the FEL pulses and can be combined with them on a sample with variable time delay. Ultrafast optical laser systems synchronised with the FEL are also available for the experiments.

Since 2012, a major upgrade is being undertaken at FLASH, with the construction of a second undulator tunnel and a new experimental hall with the aim of doubling the throughput of experiments. A fast electron beam switch is installed immediately behind the last superconducting accelerator module, enabling distribution of the accelerated and compressed electron beam to both FEL undulator lines, i.e. FLASH1 (first beamline) and FLASH2 (new). FLASH2 covers essentially the same spectral range as FLASH1, however, its variable-gap undulator enables two experiments taking data at two distinct wavelengths quasi- simultaneously. In addition to the SASE mode used in FLASH1, seeding options are considered for the extension to improve beam quality. It is planned to start user experiments on FLASH2 in 2016, with initially two beamlines.

Beam parameters


Photon energy [eV]

25 - 300

Average FEL pulse energy [µJ]

10 - 500

Pulse duration [fs] (FWHM)

<50 - 200

Peak power [GW]

1 - 3

Spectral width [%] (FWHM)

0.7 – 2

Number of pulses per second

10 - 6000 (in bunch trains at 10 Hz)

FEL mode



Linear (horizontal)