FLASH free-electron laser single-shot temporal diagnostic: terahertz-field-driven streaking

We report on the commissioning of a terahertz (THz) field driven streak camera installed at the free-electron laser FLASH at DESY in Hamburg, being able to deliver the photon pulse duration as well as the arrival time information with around 10 fs resolution for each single XUV FEL pulse. Pulse durations between 300 fs and <15 fs have been measured for different FLASH FEL settings. A comparison between the XUV pulse arrival time and the FEL electron bunch arrival time measured at the FLASH linac section - exhibit a correlation width of 20 fs rms, thus demonstrating the excellent operation stability of FLASH. In addition, the THz streaking setup was operated simultaneously to an alternative method to determine the FEL pulse duration based on spectral analysis. FLASH pulse duration, derived from simple spectral analysis, are in good agreement with that from THz streaking measurement

FLASH free-electron laser single-shot temporal diagnostic: terahertz-field-driven streaking

We report on the commissioning of a terahertz (THz) field driven streak camera installed at the free-electron laser FLASH at DESY in Hamburg, being able to deliver the photon pulse duration as well as the arrival time information with around 10 fs resolution for each single XUV FEL pulse. Pulse durations between 300 fs and <15 fs have been measured for different FLASH FEL settings. A comparison between the XUV pulse arrival time and the FEL electron bunch arrival time measured at the FLASH linac section - exhibit a correlation width of 20 fs rms, thus demonstrating the excellent operation stability of FLASH. In addition, the THz streaking setup was operated simultaneously to an alternative method to determine the FEL pulse duration based on spectral analysis. FLASH pulse duration, derived from simple spectral analysis, are in good agreement with that from THz streaking measurement

Single-shot transverse coherence measurements with Young's double pinholes at FLASH2

We measured the transverse coherence at FLASH2, a variable gap undulator line at the FLASH free-electron laser user facility at DESY in Hamburg. We demonstrate, theoretically and experimentally, a revised version of Young's double pinhole approach to perform single-shot, repeatable and non-invasive transverse coherence measurements. At beamline FL24 of FLASH2, the transverse coherence of pulses was systematically characterized at wavelengths of 8, 13.5 and 18 nm for different FEL source settings. We determine degrees of coherence of 57% to 87% in the vertical and horizontal direction, respectively. These measurements can facilitate the planning of novel, coherence-based experiments at the FLASH facility

The soft X‐ray and XUV split‐and‐delay unit at beamlines FL23/24 at FLASH2

A split‐and‐delay unit for the extreme ultraviolet and soft X‐ray spectral regions has been built which enables time‐resolved experiments at beamlines FL23 and FL24 at the Free‐electron LASer in Hamburg (FLASH). Geometric wavefront splitting at a sharp edge of a beam splitting mirror is applied to split the incoming soft X‐ray pulse into two beams. Ni and Pt coatings at grazing incidence angles have been chosen in order to cover the whole spectral range of FLASH2 and beyond, up to hν = 1800 eV. In the variable beam path with a grazing incidence angle of ϑd = 1.8°, the total transmission (T) ranges are of the order of 0.48 0.50 for 100 eV 0.06 for hν 0.61 with the Ni coating and T > 0.23 with a Pt coating is achieved. Soft X‐ray pump/soft X‐ray probe experiments are possible within a delay range of −5 ps < Δt < +18 ps with a nominal time resolution of tr = 66 as and a measured timing jitter of tj = 121 ± 2 as. First experiments with the split‐and‐delay unit determined the averaged coherence time of FLASH2 to be τc = 1.75 fs at λ = 8 nm, measured at a purposely reduced coherence of the free‐electron laser.The properties of the recently installed split‐and‐delay unit at beamlines FL23 and FL24 at FLASH2 are presented. Its operational range, performance parameters and results of a first experiment are described. imag

An X-ray gas monitor for free-electron lasers

A novel X-ray gas monitor (XGM) has been developed which allows the measurement of absolute photon pulse energy and photon beam position at all existing and upcoming free-electron lasers (FELs) over a broad spectral range covering vacuum ultraviolet (VUV), extreme ultraviolet (EUV) and soft and hard X-rays. The XGM covers a wide dynamic range from spontaneous undulator radiation to FEL radiation and provides a temporal resolution of better than 200 ns. The XGM consists of two X-ray gas-monitor detectors (XGMDs) and two huge-aperture open electron multipliers (HAMPs). The HAMP enhances the detection efficiency of the XGM for low-intensity radiation down to 10$^5$ photons per pulse and for FEL radiation in the hard X-ray spectral range, while the XGMD operates in higher-intensity regimes. The relative standard uncertainty for measurements of the absolute photon pulse energy is well below 10%, and down to 1% for measurements of relative pulse-to-pulse intensity on pulses with more than 10$^{10}$ photons per pulse. The accuracy of beam-position monitoring in the vertical and horizontal directions is of the order of 10 µm

Free-electron laser temporal diagnostic beamline FL21 at FLASH

A beamline for temporal diagnostics of extreme ultraviolet (XUV) femtosecond pulses at the free-electron laser in Hamburg (FLASH) at DESY was designed, built and put into operation. The intense ultra-short XUV pulses of FLASH fluctuate from pulse to pulse due to the underlying FEL operating principle and demand single-shot diagnostics. To cope with this, the new beamline is equipped with a terahertz field-driven streaking setup that enables the determination of single pulse duration and arrival time. The parameters of the beamline and the diagnostic setup as well as some first experimental results will be presented. In addition, concepts for parasitic operation are investigated

A synchronized VUV beamline for time domain two-color dynamic studies at FLASH2

We present a HHG-based vacuum ultraviolet (VUV) source at the free electron laser FLASH2. The source provides ultrashort pulses from 10 to 40 eV, coupled to the REMI end-station (beamline FL26) for VUV-FEL pump-probe experiments

A synchronized VUV light source based on high-order harmonic generation at FLASH

Ultrafast measurements in the extreme ultraviolet (XUV) spectral region targeting femtosecond timescales rely until today on two complementary XUV laser sources: free electron lasers (FELs) and high-harmonic generation (HHG) based sources. The combination of these two source types was until recently not realized. The complementary properties of both sources including broad bandwidth, high pulse energy, narrowband tunability and femtosecond timing, open new opportunities for two-color pump-probe studies. Here we show first results from the commissioning of a high-harmonic beamline that is fully synchronized with the free-electron laser FLASH, installed at beamline FL26 with permanent end-station including a reaction microscope (REMI). An optical parametric amplifier synchronized with the FEL burst mode drives the HHG process. First commissioning tests including electron momentum measurements using REMI, demonstrate long-term stability of the HHG source over more than 14 hours. This realization of the combination of these light sources will open new opportunities for time-resolved studies targeting different science cases including core-level ionization dynamics or the electron dynamics during the transformation of a molecule within a chemical reaction probed on femtosecond timescales in the ultraviolet to soft X-ray spectral region

Synchronized HHG based source at FLASH

We present a VUV beamline installed as pump-probe source at the free-electron laser FLASH. The source is based on high-order harmonic generation driven by femtosecond near-infrared laser pulses synchronized with the FEL burst mode