U. Hahn

Study of the statistical properties of the radiation from a VUV SASE FEL operating in the femtosecond regime

The Free-Electron Laser (FEL) at the TESLA Test Facility at DESY operates in the self-amplified spontaneous emission mode and generates sub-100-fs radiation pulses in the vacuum ultraviolet spectral region. During operation in the saturation regime, radiation pulses with GW peak power are produced. The statistical properties of the FEL radiation have been studied for different amplification regimes as well as behind a narrow-band monochromator and found to be in good agreement with the results of numerical simulations. Information about the spectral and temporal structure of the FEL radiation has been deduced from the statistical properties. The pulse duration of the FEL radiation can be varied by tailoring the electron bunch that drives the FEL.

Gas‐Monitor Detector for Intense and Pulsed VUV/EUV Free‐Electron Laser Radiation

In the framework of current developments of new powerful VUV and EUV radiation sources, like VUV free‐electron‐lasers or EUV plasma sources for 13‐nm lithography, we developed a gas‐monitor detector in order to measure the photon flux of highly intense and extremely pulsed VUV and EUV radiation in absolute terms. The device is based on atomic photoionization of a rare gas at low particle density. Therefore, it is free of degradation and almost transparent, which allows the detector to be used as a continuously working beam‐intensity monitor. The extended dynamic range of the detector allowed its calibration with relative standard uncertainties of 4% in the Radiometry Laboratory of the Physikalisch‐Technische Bundesanstalt at the electron‐storage ring BESSY II in Berlin using spectrally dispersed synchrotron radiation at low photon intensities and its utilization for absolute photon flux measurements of high power sources. In the present contribution, we describe the design of the detector and its applicat...

Alignment of the optical feedback system of VUV regenerative FEL amplifier at the TESLA test facility at DESY

In this paper, we describe optical feedback system of VUV Regenerative FEL Amplifier (RAFEL) at the TESLA test facility at DESY. The aim of the RAFEL experiment is to construct fully coherent, tunable VUV radiation source by means of applyingnarrow-band optical feedback in the VUV SASE FEL operatingcurrently at DESY. One of the problem of the realization of the RAFEL is severe requirements for the angular stability of the optical elements (about few microradians). This problem has been solved by means of installation of active alignment system with reference laser. Another problem is alignment of optical elements separated by 65 m within complicated experimental conditions connected with aperture limitations (down to 6 mmÞ: This problem has been solved in two steps. Preliminary alignment with an accuracy of about 80 mrad has been performed with laser alignment system and OTR screens used at the TTF accelerator for electron beam diagnostics. Final alignment has been performed with VUV SASE FEL radiation. Measured feedback coefficient is about 1 percent and is in agreement with the designed value. r 2002 Elsevier Science B.V. All rights reserved. PACS: 41.60.Cr; 52.75.M; 42.62.Cf

The SASE FEL at DESY: Photon Beam Diagnostics for the User Facility

We present an overview of the vacuum‐ultraviolet free electron laser (VUV FEL) user facility at DESY comprising the layout of the experimental hall, radiation transport to the experimental area, as well as photon beam diagnostics. In general, diagnostics of the FEL radiation is particularly challenging due to the laser’s unique properties such as extremely high peak powers and short pulse lengths. Yet, pulse‐resolved characterization of the photon beam is essential for most user experiments. In order to monitor important parameters like radiation pulse intensity, spectral distribution, etc. new concepts have been developed allowing efficient use of the new source.