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 is in operation in Hamburg since 2016 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 acceleratation of 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.

At FLASH1, femtosecond coherent light pulses emerge from the 30 m long fix-gap undulator in the accelerator tunnel and can be delivered alternatively to five experimental stations in the FLASH1 experimental hall ‘Albert Einstein’ by a photon beam transport system operating under ultra-high vacuum conditions. 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 up to ~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 2016, an additional FEL undulator line in a separate tunnel - FLASH2- and the new FLASH experimental hall 'Kai Siegbahn' are operated as a user facility adjacent to the original FLASH facility now called FLASH1. 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. FLASH2 covers essentially the same spectral range as FLASH1, however, its variable-gap undulators enable additional operation options. First lasing of FLASH2 was achieved in August 2014 in parallel to FLASH1. Therefore, the FLASH facility at DESY now comprises two separate and almost independent FEL sources. This upgrade significantly enhances the capacities for XUV and soft X-ray FEL users at DESY with the aim of doubling the throughput of experiments.

Currently, FLASH2 offers two beamlines, FL 24 and FL 26, for users. FL 24 provides a variable micro-focus and an open port for user supplied endstations, while at FL 26 the permanent end station REMI, a reaction microscope from the MPIK Heidelberg, is set up. A pulse-length compensating monochromator beamline (FL23) is currently under development. FLASH1 and FLASH2 operation parameters are detailed in the table below.

FLASH - machine parameters



Electron Energy range

0.35 - 1.25 GeV

0.4 - 1.25 Gev

Normalised emittance at 1 nC (rms)

1.4 mm mrad

1.4 mm mrad

Energy spread

200 keV

500 keV

Electron bunch charge

0.02 - 1.2 nC

0.02 - 1 nC

Peak current

1 - 2.5 kA

1- 2.5 kA

Electron bunches per second (to be shared between FL1 and FL2)



FLASH - lasing parameters



Photon energy fundamental

24 - 295 eV

14 - 310 eV

Wavelength fundamental

51 - 4.2 nm

90 - 4 nm

Photon pulse duration (FWHM)

30 - 200 fs

10 - 200 fs (estimated)

Peak power

1 - 5 GW

1 - 5 GW

Single photon pulse energy (average)

1 - 500µJ

1 - 1000µJ

Spectral width (FWHM)

0.7 - 2%

0.5 - 2%

Photons per bunch

1011 - 1014

1011 - 1014

Peak brilliance photons/sec/mm²/mrad² /0.1%

1028 - 1031

1028 - 1031