5 research outputs found
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THz Pump and X-Ray Probe Development at LCLS
We report on measurements of broadband, intense, coherent transition radiation at terahertz frequencies, generated as the highly compressed electron bunches in Linear Coherent Light Source (LCLS) pass through a thin metal foil. The foil is inserted at 45{sup o} to the electron beam, 31 m downstream of the undulator. The THz emission passes downward through a diamond window to an optical table below the beamline. A fully compressed 350-pC bunch produces up to 0.5 mJ in a nearly half-cycle pulse of 50 fs FWHM with a spectrum peaking at 10 THz. We estimate a peak field at the focus of over 2.5 GV/m. A 20-fs Ti:sapphire laser oscillator has recently been installed for electro-optic measurements. We are developing plans to add an x-ray probe to this THz pump, by diffracting FEL x rays onto the table with a thin silicon crystal. The x rays would arrive with an adjustable time delay after the THz. This will provide a rapid start to user studies of materials excited by intense single-cycle pulses and will serve as a step toward a THz transport line for LCLS-II
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Toward a Single Mode Free Electron Laser for Coherent Hard X-Ray Experiments
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Radiation Safety Aspects of the Linac Coherent Light Source Project At SLAC
The Linac Coherent Light Source (LCLS) is a Self-Amplified Spontaneous Emission based Free Electron Laser (FEL) that is being designed and built at the Stanford Linear Accelerator Center (SLAC) by a multilaboratory collaboration. This facility will provide ultra-short pulses of coherent x-ray radiation with the fundamental harmonic energy tunable over the energy range of 0.82 to 8.2 keV. One-third of the existing SLAC LINAC will compress and accelerate the electron beam to energies ranging from 4.5 GeV to 14.35 GeV. The beam will then be transported through a 130-meter long undulator, emit FEL and spontaneous radiation. After passing through the undulator, the electron beam is bent to the main electron dump. The LCLS will have two experiment halls as well as x-ray optics and infrastructure necessary to make use of the FEL for research and development in a variety of scientific fields. The facility design will incorporate features that would make it possible to expand in future such that up to 6 independent undulators can be used. While some of the radiation protection issues for the LCLS are similar to those encountered at both high-energy electron linacs and synchrotron radiation facilities, LCLS poses new challenges as well. Some of these new issues include: the length of the facility and of the undulator, the experimental floor in line with the electron beam and the occupancy near zero degrees, and the very high instantaneous intensity of the FEL. The shielding design criteria, methodology, and results from Monte Carlo and analytical calculations are presented
Real-Time Manifestation of Strongly Coupled Spin and Charge Order Parameters in Stripe-Ordered Nickelate Crystals Using Time-Resolved Resonant X-Ray Diffraction
We investigate the order parameter dynamics of the stripe-ordered nickelate, La1.75Sr0.25NiO4, using time-resolved resonant x-ray diffraction. In spite of distinct spin and charge energy scales, the two order parameters’ amplitude dynamics are found to be linked together due to strong coupling. Additionally, the vector nature of the spin sector introduces a longer reorientation time scale which is absent in the charge sector. These findings demonstrate that the correlation linking the symmetry-broken states does not unbind during the nonequilibrium process, and the time scales are not necessarily associated with the characteristic energy scales of individual degrees of freedom