Free-electron laser FLASH

First lasing at 4.45 nm

For the first time, FLASH produced laser light with a wavelength of 4.45 nanometers.
FLASH, DESY's free-electron laser for soft X-ray light considerably beats its previous record of 6.5 nanometers. At the same time, the peak intensity of single light pulses nearly doubled, with 0.3 millijoule. Prior to this, there was a five-month machine upgrade, above all with a significant improvement of the superconducting linear accelerator and the installation of a seeding experiment together with the University of Hamburg.
FLASH, the world’s first X-ray free-electron laser is available to the photon science user community for experiments since 2005. Last winter, the facility underwent a major upgrade. The accelerator was equipped with a seventh superconducting accelerator module to increase the maximum electron energy to 1.2 Giga electron volts (GeV). Moreover, a special 3.9-GHz module was installed to improve the quality of the accelerated electron bunches. The first tests during the current commissioning showed excellent results: the linear accelerator was operated at 1.207 GeV and the 3.9-GHz module shapes the electron bunches in a way that the intensity of the laser light is higher than ever before.
„It is absolutely impressing, how fast and promising FLASH is operating after such a substantial upgrade. My compliments to the FLASH accelerator team,” congratulates Reinhard Brinkmann, director of the DESY accelerator section. With the now obtainable laser wavelength, experiments with carbon in organic molecules come within reach, and magneto-dynamics experiments with the third-harmonic wavelength benefit from substantially increased intensities. This success is also an important milestone for the European XFEL on the way to the observation of movements that only take femtoseconds. The accelerator module recently built-in at FLASH is a prototype for the XFEL accelerator, and the properties of the 3.9-GHz module too are decisive for operating the XFEL injector. The third FLASH user period is to start this summer."

Many other improvements of FLASH have been completed. As an example, the RF-stations and waveguide distribution have been substantially upgraded. The injector has now a new RF gun, an upgraded laser system and a new booster module.
sFLASH, the seeding experiment is being commissioned now. An external laser overlaps with the electron beam to seed the SASE process in a series of new undulators installed between the accelerator and the FLASH undulators.

FLASH, DESY's free-electron laser is a world-wide unique facility delivering intense ultra-short femtosecond coherent radiation in the wavelength range between 47 and 6.8 nm.
With the successful upgrade, wavelengths below 5 nm are now within reach.

Since 2005, FLASH is a user facility serving a large variety of experiments.
Typical user operation parameters during the 2nd user period from Nov 26, 2007 to Aug 16, 2009:

Typical user operation parameters during the 2nd user period from Nov26, 2007 to Aug16, 2009:
Wavelength range (fundamental)	6.8 - 47 nm
Average Single Pulse Energy	10 - 100 µJ
Pulse Duration (FWHM)	10 - 70 fs
Peak Power (from av.)	1 - 5 GW
Average Power (example for 500 pulses/sec)	~ 15mW
Spectral Width (FWHM)	~ 1 %
Peak Brilliance	10^29 - 10^30 photons/s/mrad2/mm2/0.1%bw

Many scientific disciplines ranging from physics, chemistry and biology to material sciences, geophysics and medical diagnostics use
the powerful soft X-ray source FLASH. The ultra-short X-ray pulses in the femtosecond range allow experiments which are not possible otherwise. For example, time-resolved observation of chemical reactions with atomic resolution, single shot diffraction imaging, and many others.
More than 60 publications on photon science have been published already, many in high ranked journals.

FLASH is a high-gain free-electron laser (FEL) which achieves laser amplification and saturation within a single pass of the electron
bunch through an undulator and does not require a set of mirrors which is needed in conventional lasers. The lasing process is initiated by the spontaneous undulator radiation, and the FEL works then in the so-called Self-Amplified Spontaneous Emission (SASE) mode without needing an external input signal.The electron bunches are produced in a laser-driven photoinjector and accelerated by a superconducting linear accelerator. The RF-gun based photoinjector allows the generation of electron bunches with tiny emittances - mandatory for an efficient SASE process.The superconducting techniques allows to accelerate thousands of bunches per second, which is not possible with other technologies. At intermediate energies of 130 and 470 MeV the electron bunches are longitudinally compressed, thereby increasing the peak current from initially 50-80 A to 1-2 kA - as required for the lasing process in the undulator. The 30 m long undulator consists of permanent NdFeB magnets with a fixed gap of 12 mm, a period length of 27.3 mm and peak magnetic field of 0.47 T. The electrons interact with the undulator field in such a way, that so called micro bunches are developed. These micro bunches radiate coherently and produce intense X-ray pulses. Finally, a dipole magnet deflects the electron beam safely into a dump, while the FEL radiation propagates to the experimental hall.

Picture gallery of the FLASH linac
updated in May 2008