[en] For the proof-of-principle experiment of self-amplified spontaneous emission (SASE) at short wavelengths on the VUV FEL at DESY a multi-facetted photon beam diagnostics experiment has been developed employing new detection concepts to measure all SASE specific properties on a single pulse basis. The present setup includes instrumentation for the measurement of the energy and the angular and spectral distribution of individual photon pulses. Different types of photon detectors such as PtSi-photodiodes and fast thermoelectric detectors based on YBaCuO-films are used to cover some five orders of magnitude of intensity from the level of spontaneous emission to FEL radiation at saturation. A 1 m normal incidence monochromator in combination with a fast intensified CCD camera allows to select single photon pulses and to record the full spectrum at high resolution to resolve the fine structure due to the start-up from noise

[en] Full text: A stigmatic grazing-incidence spectrometer for the 2.5-40 nm EUV region has been realized. The optical design consists of a grazing-incidence spherical variable-line-spaced grating with flat-field properties coupled to a spherical focusing mirror that compensates for the astigmatism. The mirror is mounted with its tangential plane coincident with the equatorial plane of the grating in the Kirkpatrick-Baez configuration. The spectrum is acquired by an EUV-enhanced CCD detector, that can be moved along the spectral focal curve to select the spectral region to be acquired. This stigmatic design has also spectral and spatial resolution capability for extended sources. The spectral and spatial resolution of the system have been characterized by using the emission from an hollow-cathode lamp or a laser-produced plasma. The instrument is going to be installed at the DESY synchrotron for the spectral monitoring of the EUV FEL beam in the 20-40 nm region

[en] 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

[en] A nondestructive radiation detector unit is under construction at the TESLA Test Facility at DESY providing monitoring of the radiation (pulse energy, transverse intensity distribution, and statistical properties). The concept of the detector design is based on experience obtained during operation of TTF FEL, Phase 1. Key element of the detector is a wide dynamic range micro-channel plate (MCP) which detects scattered radiation from a thin gold wire crossing photon beam. Operating wavelength range of the detector is from 6 to 100 nm. An important feature of the MCP-based detector is that it is capable to cover all dynamic range of the radiation intensity, from the level of spontaneous emission up to the saturation level of SASE FEL

[en] FLASH, the Free-electron LASer in Hamburg, is a worldwide unique source for extremely bright ultra-short laser-like pulses tunable in a wide spectral range in the extreme ultraviolet and soft x-ray region (Ackermann et al 2007 Nat. Photonics 1 336-42). To fully exploit the features of this new generation of light sources, a user facility with efficient radiation transport to the experimental area and novel online photon diagnostics capable of characterizing the unique parameters of the FLASH radiation has been built. It serves a broad user community active in many scientific fields ranging from atomic and molecular physics to plasma and solid state physics as well as chemistry and biology. A special focus is placed on the exploitation of the ultra-short FLASH pulses using pump-probe techniques. Thus, the facility is equipped with optical and THz sources synchronized to FLASH. This paper gives a detailed overview of the FLASH user facility.

[en] 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 applying narrow-band optical feedback in the VUV SASE FEL operating currently 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 mm). This problem has been solved in two steps. Preliminary alignment with an accuracy of about 80 μrad 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

[en] A method has been developed and applied to measure the beam waist and spot size of a focused soft x-ray beam at the free-electron laser FLASH of the Deutsches Elektronen-Synchrotron in Hamburg. The method is based on a saturation effect upon atomic photoionization and represents an indestructible tool for the characterization of powerful beams of ionizing electromagnetic radiation. At the microfocus beamline BL2 at FLASH, a full width at half maximum focus diameter of (15±2) μm was determined

[en] We have developed different types of photodetectors that are based on the photoionization of a gas at a low target density. The almost transparent devices were optimized and tested for online photon diagnostics at current and future x-ray free-electron laser facilities on a shot-to-shot basis with a temporal resolution of better than 100 ns. Characterization and calibration measurements were performed in the laboratory of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II in Berlin. As a result, measurement uncertainties of better than 10% for the photon-pulse energy and below 20 μm for the photon-beam position were achieved at the Free-electron LASer in Hamburg (FLASH). An upgrade for the detection of hard x-rays was tested at the Sub-Picosecond Photon Source in Stanford

[en] 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

[en] At the new SPring-8 extreme ultraviolet free-electron laser in Japan, a radiometric comparison between a gas-monitor detector from Physikalisch-Technische Bundesanstalt/Deutsches Elektronen-Synchrotron/Ioffe Physico-Technical Institute (Ioffe) and a cryogenic radiometer from National Institute of Advanced Industrial Science and Technology was carried out. Radiant power in the range between 30 μW and 350 μW was measured at the wavelengths of 51.3 nm, 56.1 nm and 61.2 nm. The results obtained with the two different detectors agree within 2.6%, which is well below their combined relative standard uncertainty, which varies from 4.1% to 5.5%. (authors)