|ALS Femtosecond X-ray Beamlines|
tunable x-ray pulses: 170 eV – 10 KeV, 250 fs
This research program is based on two novel femtosecond X‑ray beamlines at the Advanced Light Source. One is optimized for the soft X‑ray range (0.2–1.8 keV) and the other for the hard X‑ray range (2–10 keV). These beamlines provide ~250 fs X‑ray pulses with unprecedented average flux and brightness for time-resolved x-ray science. They offer a unique combination of wide tunability and high repetition rate and are ideal for time resolved X‑ray spectroscopy and scattering studies of structural dynamics in condensed phases.
Both femtosecond beamlines presently share a single in-vacuum undulator/wiggler (U3) which provides undulator harmonics up to ~1.8 keV for the soft x-ray beamline, and wiggler emission up to 10 keV for the hard x-ray beamline. Separate, moveable primary focusing mirrors are used to provide x-rays to either the soft or hard x‑ray branch. The present installation (beamlines, undulator, and storage-ring sector) is already configured to accommodate in the future a separate elliptically-polarized undulator (EPU), which will be dedicated to the soft x-ray beamline and will provide complete polarization control for x-ray dichroism spectroscopy.
Both hard and soft x-ray beamlines include high-speed choppers to match the x-ray duty cycle to that of the femtosecond excitation laser, as well as a pair of slits in the image plane for selecting either the femtosecond x-ray pulses or the 70 ps x-ray pulses (at full flux, ~×104 increase per pulse). The soft x‑ray beamline consists of a varied-line-spacing grating spectrograph providing a spectral resolving power of ~1/2000. The beamline is designed to incorporate two sample chambers: one at the entrance of the spectrograph for pink-beam experiments with detection of the dispersed transmission spectrum; and a second at the exit of the spectrograph for monochromatic measurements. A special soft x-ray endstation chamber has been developed for transient x-ray absorption measurements in thin liquid films (~1 μm thickness) contained within a silicon-nitride cell. The hard x-ray beamline consists of a cryogenically cooled double-crystal monochromator providing a resolution of ~1/3000, and an endstation chamber with a goiniometer, manupilator, and wire-guided jet for liquid samples, all located in a hutch. A 10 kHz femtosecond laser system (~60 W total output power) combined with an optical parametric amplifier, provides pulses over a range of wavelengths (via nonlinear mixing) for sample excitation at both beamlines, with absolute synchronization to the femtosecond x-ray pulses
a) Soft X-ray Endstation for Nanofluidic Cells b) Hard X-ray Endstation for Liquid Jets