SXR End Stations

There will be an experimental station before the monochromator, experimental position 1, where samples can be introduced into the unfocused , ~1 mm in diameter, beam. Several detection methods are potentially possible. The proposal is to concentrate on transmission through thin samples, using the monochromator in spectrograph mode, with a detector at the exit slit to measure absorption spectra.

The absorption experimental set up is simple. An x-y manipulator is required to position the samples in the beam. The sample positioning system does not need to be high precession due to the large beam size. There will be a camera to monitor sample position and to align the FEL, the pump laser and an alignment laser into overlapping phase space at the sample position. The sample positioner will carry a number of samples which will include a Ce doped YAG crystal for alignment of the FEL pulse.

The sample chamber will be isolated from the SOMS and the monochromator optics by an all metal gate valve. The chamber will have an ion pump for UHV operation and a cold cathode gauge to monitor the pressure. The pressure in this system will have to be <5 x 10^-9 torr to be opened to either the monochromator or the SOMS system. Samples will have to be UHV compatible.

The shielding requirements for this sample system have not been determined, but it should be anticipated that samples cannot be run in this system unless personnel are excluded from the first hutch. Access to the first hutch with samples in the beam can only be permitted when proper shielding has been defined, implemented and qualified.

The RSXS end station can perform time-resolved pump-probe resonant soft X-ray scattering (diffraction) to study the temporal dynamics of the charge/spin/orbital orders in solid state materials. This end station has a base pressure better than 10^-8 torr, and a high vacuum compatible sample loading/transfer system is installed for the rapid change of samples. A motorized sample stage allows the sample to be rotated azimuthally about its surface normal (Φ) and be pivoted in the vertical plane (χ). This sample stage (also shown in the following figure) is thermally contacted to a temperature control system, which consists of a liquid Helium cryostat and a heater, allowing the sample temperature to be changed from 15 K to 400 K. There are total six degrees of freedom for the sample: three translational (x, y, z from manipulator) and three rotational degrees of freedom (Θ,χ,Φ) with a differentially pumped rotary seal.

This end station has the following detectors: two avalanche photodiodes, one thermopile detector (for detecting IR radiation) and will have a fast area detector in the near future (note: the FCCD in the image is currently not installed). These detectors are mounted on a fully motorized detector stage inside the vacuum chamber, which allows those detectors to move in both horizontal (360 degrees) & vertical (90 degrees) scattering planes. Such capability can be used to efficiently search for superlattice reflections over the full range of reciprocal space. X-ray absorption (XAS) can also be performed by measuring the fluorescent yield and total electron yield (sample-to-ground current).

Based on a differentially pumped liquid jet system design, the LCLS liquid jet endstation (LJE) is equipped with a newly commissioned X-ray emission spectrometer. The varied line-space plane grating spectrometer is optimized to operate for detection from 250 eV to 2000 eV with a resolving power of 1500 to as high as 3000 at lower energies.  The LJE can support various time-resolved pump-probe X-ray emission and/or X-ray absorption experiments examining the ultrafast dynamics for an array of liquid chemistry studies and investigating valence electronic structure and the chemical state for chemically and biologically relevant molecular dynamics. Additionally, X-ray induced radiation chemistry can be investigated through femtosecond time resolved X-ray-pump/optical-probe spectroscopy.

The endstation is in use at LCLS and BESSY-II (Berlin, Germany). Complementary experiments at BESSY are encouraged. Please contact us for more information. For further reading a description of the setup is published:

Kunnus, K. et al.: "A setup for resonant inelastic soft X-ray scattering on liquids at free electron laser light sources" Rev. Sci. Instrum. 83 123109 (2012); doi: 10.1063/1.4772685

The Surface Chemistry endstation, outlined in the figure above, is designed for soft X-ray photoelectron spectroscopy (PES), X-ray emission spectroscopy (XES) and X-ray adsorption spectroscopy (XAS) of surface and solid state samples of up to 10mm in diameter having ultra-high vacuum compatibility. The end station is equipped with an electron spectrometer (R3000, VG-Scienta) for PES and a soft X-ray emission spectrometer housing 2 gratings for photon energies from about 220 eV to 630 eV with a maximum resolving power of about 2000. A manipulator (VG Omniax) allows transfer of the sample(s) between the preparation chamber and the analysis chamber. Sputtering facilities, evaporation sources, mass spectrometer and LEED optics are available in the preparation chamber.

The sample setup, illustrated in the figure above, is optimized for studies of adsorbate systems prepared on single crystal surfaces. Temperatures between 30 and 1500 K can be achieved through cooling with liquid N₂ (He) and heating performed by electron bombardment (with or without a bias). Temperature is measured by thermocouples connected to the sample.

The Surface Chemistry endstation has been tested and operated at BL 13-2 at SSRL and provided results at LCLS (1-3). The endstation owners intend to further develop this endstation for more dedicated use at LCLS.

The endstation is designed for soft X-ray resonant single-shot imaging (Fourier Transform Holography and Coherent Diffractive Imaging), small angle resonant scattering and optical pump - X-ray probe of fixed targets in transmission geometry with focus on magnetization dynamics and phase transitions. The system will run under HV conditions (~10^-8 to 10^-7 torr). Compatible to the design of the existing soft X-ray coherent imaging endstation at SSRL beamline 13-3, see figure, the main chamber has a XYZ-theta manipulator (Omniax) with a cryostat providing a temperature range of 25-400 K. The endstation is further equipped with a breadboard allowing for modular experimental setups including an aperture and a sample stage as well as beam diagnostics and timing tools for optical and X-ray beam synchronization.

A commercial in-vacuum CCD detector from Princeton Instruments, PI-MTE, is integrated in the system together with beam stops suitable for operation at higher X-ray flux. The CCD contains 2048 x 2048 pixels of 13 microns in size. A removable 500 nm Al thin filter supported on a 200 nm thick polymer is used to block the optical photons for pump-probe experiments. Optional, the endstation is capable of accommodating the flange-mounted large-area, pnCCD detector of the LAMP endstation enabling higher frame read-out rate up to 200 Hz (back pnCCD only). Removable pole pieces of an ex-situ electro-magnet will provide magnetic fields (~.1 Tesla) applied along the X-ray beam propagation. An in-vacuum electromagnet can used to obtain constant fields up to 0.4 Tesla.

Currently under development the qRIXS station is optimized for time-resolved and momentum-resolved resonant inelastic X-ray scattering (qRIXS). The goal of this endstation is to study the dynamics of charge/spin excitations of solids in both time and energy domains, especially focus on the L-edge of the transition metal oxide and M-edge of the rare earth elements. The endstation will be equipped with three emission spectrographs. The spectrographs will have a maximum resolving power around 5000 at 540 eV incident photon energy. They will be self-supported by kinetic mounts on the support platform on top of a hexapod structure. Five mounting ports with an angular interval of 25 degrees in the horizontal scattering plane and +/-15 degrees of endstation rotation relative to the incident photon beam (achieved by moving the hexapod) allows the scattered X-rays in the angular range of 25 ~ 155 degrees to be recorded. This design allows the users to probe a wide range of momentum transfer. The spectrograph is necessary for the time-resolved pump-probe inelastic scattering experiment, as it can record a spectrum across a range of energy loss simultaneously. This endstation will also be equipped with avalanche photodiodes for measuring the total fluorescence yield as diagnostic XAS curves for the RIXS experiment. The sample stage is electrically isolated from ground such that the total electron yield can also be recorded. This endstation is expected to be commissioned in 2015. An additional spectrograph with polarization analyzer will become available in 2016.

The Electron Beam Ion Trap (EBIT) endstation, outlined in the figures, is a system dedicated to the investigation of the interaction of light with dilute clouds of trapped highly charged ions (HCI). It is especially designed to explore the interaction of photons with highly charged ions in any desired charge state. Such ions are ubiquitous in astrophysics and high temperature plasmas, and have also important applications for studies of fundamental interactions.

Scientific goals include: The determination of photoionization and photoabsorption cross sections, both of utmost importance for astrophysics; the production, trapping and investigation of photoionized samples of strongly correlated warm, dense plasmas, this point representing one of the forefront topics of present plasma physics research; the direct photo-excitation of low-lying nuclear levels, which would imply a significant advance in nuclear physics. Precision measurements on the electronic level structure of HCIs shall be performed to test fundamental theories (QED) and parity non-conservation in the neutral currents sector. Future work will also aim at the preparation and control of highly excited coherent quantum states with combined XFEL and optical lasers.

The endstation consists of a fully operational EBIT. It is equipped with various spectrometers for visible, VUV, X-ray or fluorescence photon detection, including an X-ray microcalorimeter. Eight ports transverse to the LCLS beam give access for intense lasers into the trap region as well as for injecting gaseous targets. One axial port permits ion/photoion extraction and charge analysis of the extracted ions on a position-sensitive detector. The complete endstation requires ~4 x 2 m² floor space and weights about 2 tons. It is further equipped with diagnostic tools to guarantee the overlap between the LCLS beam with the ion cloud and to measure the photon beam energy in a pulse-by-pulse mode. The present transportable EBIT endstation operation has been tested at the soft X-ray free electron laser FLASH, as well as at the BESSY II and PETRA III synchrotrons. The collaboration intends to develop and commission a new, dedicated user EBIT endstation for LCLS after the initial experimental phase.