The plane grating monochromator beamline U49-2 PGM-1 at BESSY II

U49/2 PGM1 is one of HZB open-port VUV beamlines. Therefore and due to the fact that it delivers highest flux with very acceptable energy resolution it is the most heavily booked BESSY II beamline. Earlier work has largely focused on surface science and catalysis. After shut down of the former U41 PGM an increasing number of experiments on liquids and solutions are carried out

The PM3 beamline at BESSY II

PM3 merges the developments of the former BESSY I SX700 III monochromator for elliptically polarized VUV radiation and of BESSY II collimated plane grating monochromators. This way it is possible to achieve circular polarization from a BESSY II dipole in the range 20 – 2000 eV with high photon flux, high energy resolution and high stability

UE112_PGM-1: An open-port low-energy beamline at the BESSY II undulator UE112

The X-ray optical and mechanical designs of a low-energy high-flux VUV- to soft-X-ray beamline for photon energies between 17 and 200 eV (with lower flux up to 690 eV) are presented

The FemtoSpeX facility at BESSY II

The FemtoSpeX facility of the BESSY II storage ring is dedicated to ultrafast optical-pump & soft  x-ray probe experiments. Experimental end-stations for experiments in transmission, reflection, and diffraction geometry are available

Hot electron driven enhancement of spin-lattice coupling in 4f ferromagnets observed by femtosecond x-ray magnetic circular dichroism

Femtosecond x-ray magnetic circular dichroism was used to study the time-dependent magnetic moment of 4 fs electrons in the ferromagnets Gd and Tb, which are known for their different spin-lattice coupling. We observe a two-step demagnetization with an ultrafast demagnetization time of 750 fs identical for both systems and slower times which differ sizeably with 40 ps for Gd and 8 ps for Tb. We conclude that spin-lattice coupling in the electronically excited state is enhanced up to orders of magnitude compared to equilibrium.Comment: added reference 24, clarified the meaning of photo-induced, emphasized that XMCD probes the magnetic moment localized at 4f electron

a versatile optical pump–soft X-ray probe facility with 100 fs X-ray pulses of variable polarization

Here the major upgrades of the femtoslicing facility at BESSY II (Khan et al., 2006) are reviewed, giving a tutorial on how elliptical-polarized ultrashort soft X-ray pulses from electron storage rings are generated at high repetition rates. Employing a 6 kHz femtosecond-laser system consisting of two amplifiers that are seeded by one Ti:Sa oscillator, the total average flux of photons of 100 fs duration (FWHM) has been increased by a factor of 120 to up to 106 photons s-1 (0.1% bandwidth)-1 on the sample in the range from 250 to 1400 eV. Thanks to a new beamline design, a factor of 20 enhanced flux and improvements of the stability together with the top-up mode of the accelerator have been achieved. The previously unavoidable problem of increased picosecond- background at higher repetition rates, caused by `halo' photons, has also been solved by hopping between different `camshaft' bunches in a dedicated fill pattern (`3+1 camshaft fill') of the storage ring. In addition to an increased X-ray performance at variable (linear and elliptical) polarization, the sample excitation in pump-probe experiments has been considerably extended using an optical parametric amplifier that supports the range from the near-UV to the far-IR regime. Dedicated endstations covering ultrafast magnetism experiments based on time-resolved X-ray circular dichroism have been either upgraded or, in the case of time-resolved resonant soft X-ray diffraction and reflection, newly constructed and adapted to femtoslicing requirements. Experiments at low temperatures down to 6 K and magnetic fields up to 0.5 T are supported. The FemtoSpeX facility is now operated as a 24 h user facility enabling a new class of experiments in ultrafast magnetism and in the field of transient phenomena and phase transitions in solids

Analysis of the halo background in femtosecond slicing experiments

The slicing facility FemtoSpeX at BESSY II offers unique opportunities to study photo-induced dynamics on femtosecond time scales by means of X-ray magnetic circular dichroism, resonant and non-resonant X-ray diffraction, and X-ray absorption spectroscopy experiments in the soft X-ray regime. Besides femtosecond X-ray pulses, slicing sources inherently also produce a so-called `halo' background with a different time structure, polarization and pointing. Here a detailed experimental characterization of the halo radiation is presented, and a method is demonstrated for its correct and unambiguous removal from femtosecond time-resolved data using a special laser triggering scheme as well as analytical models. Examples are given for time-resolved measurements with corresponding halo correction, and errors of the relevant physical quantities caused by either neglecting or by applying a simplified model to describe this background are estimated