Status of sFLASH, the Seeding Experiment at FLASH

Recently, the Free electron LASer in Hamburg FLASH at DESY has been upgraded considerably [1]. Besides increasing the maximum energy to about 1.2 GeV and installation of a third harmonic rf cavity linearizing the longitudinal phase space distribution of the electron bunch, an FEL seeding experiment at wavelengths of about 35 nm has been installed. The goal is to establish direct FEL seeding employing coherent VUV pulses produced from a powerful drive laser by high harmonic generation HHG in a gas cell. The project, called sFLASH, includes generation of the required HHG pulses, transporting them to the undulator entrance of a newly installed FEL amplifier, controlling spatial, temporal and energy overlap with the electron bunches and setting up a pump probe pilot experiment. Sophisticated diagnostics is installed to characterize both HHG and seeded FEL pulses, both in time and frequency domain. Compared to SASE FEL pulses, almost perfect longitudinal coherence and improved synchronization possibilities for the user experiments are expected. In this paper the status of the experiment is presente

sFLASH - Present Status and Commissioning Results.

The sFLASH-experiment has been built at the Free-Electron Laser in Hamburg (FLASH) to study the high-gain-FEL amplification of a laser seed from a high harmonic generation (HHG) source. Ideally, the HHG-seed can be amplified up to a GW-power level, improving both the shot-to-shot stability and the longitudinal coherence of the FEL-pulse. In 2010/2011 the sFLASH-components and sub-systems have been fully installed and commissioned within about 300 hours FLASH beam time dedicated to the seeding project. Procedures to achieve a full six-dimensional overlap between the seed and the electron bunch have been developed and tested. An important milestone reached in the commissioning period is the sFLASH-SASE lasing mode, which was being achieved on a regular basis. A step forward towards the next milestone - the direct seeding in the XUV-wavelength range - is the sFLASH-upgrade during the planed FLASH-shutdown in autumn 2011. In this contribution the main commissioning results and highlights of the operational experience will be discussed in detail

First Direct Seeding at 38 nm

The sFLASH project at DESY is an experiment to study direct seeding using a source based on the high-harmonic generation (HHG) process. In contrast to SASE, a seeded FEL exhibits greatly improved longitudinal coherence and higher shot-to-shot stability (both spectral and energetic). In addition, the output of the seeded FEL is intrinsically synchronized to the HHG drive laser, thus enabling pump-probe experiments with a resolution of the order of 10 fs. The installation and successful commissioning of the sFLASH components in 2010/2011 has been followed by a planned upgrade in autumn 2011. As a result of these improvements, in spring 2012 direct HHG seeding at 38 nm has been successfully demonstrated. In this contribution, we describe the experimental layout and announce the first seeding at 38 nm