Focusing Hard X-rays at Current and Future Light Sources for Microscopy and High-Power Applications
The field of x-ray optics struggles to develop optical systems with the versatility and sophistication of their visible light counterparts. The advent of fourth-generation light sources will make the struggle even more difficult. Fourth-generation light sources include laser/plasma sources, x-ray Free Electron Lasers (FEL), inverse Compton scattering sources, and the National Ignition Facility. LCLS, (Linac Coherent Light Source), and its European cousin, will be the first of the x-ray FELs. The LCLS, to be built at the Stanford Linear Accelerator Center (SLAC), takes advantage of the existing SLAC linear accelerator to send intense, low emittance electron bunches through a 100 m long undulator structure. Through a process called SASE (Self Amplification of Spontaneous Emission) the electrons interact with the radiation fields they produce while in the undulator causing them to collect into micro bunches that emit coherent light. In the case of the LCLS the coherent radiation will have a wavelength in the x-ray regime, and will be tunable from 1.5 to 15 {angstrom}. The LCLS will deliver x-rays in individual coherent packages lasting < 300 fs, making the LCLS a very important source for studying short time phenomenon and for performing high-resolution x-ray structural analysis of molecular sized systems. Moreover, each coherent packet packs 10{sup 12} photons in a very small volume of space- time; the interaction of this packet with matter, and the subsequent aftermath offer new opportunities in physics. To make full use of the LCLS, experimenters must be able to manipulate and focus the LCLS beam, and therefore must contend with the fact that the unprecedented energy density per unit area in the FEL beam is enough to melt most materials in a single pulse. Take the example of the Warm Dense Matter experiment, in which LLNL researchers hope to use a focused LCLS beam to instantly (that is fast enough that the density doesn't change) bring solid pieces of matter to a plasma state. The experiment operates with an 8 keV photon beam, and although the focusing requirements are modest, present-day x-ray optics that can meet these requirements will melt when exposed to the beam from the LCLS according to figure 2. Figure 2 suggests that lower Z materials like beryllium, lithium, and carbon would fare better at the LCLS and that optics fabricated from low Z materials might offer a solution to the problem of survivable optics for the Warm Dense Matter experiment. Now both reflective and refractive x-ray optics are in use at these wavelengths, with reflective optics dominating because standard techniques have been developed for their manufacture. Common reflective optics make use of high Z materials which give higher performance. The less common refractive optics are also made of high Z materials but would work better if fabricated from low Z materials, which have less absorption. Based on these arguments it seems that low Z refractive optics would be the optics of choice for the Warm Dense Matter experiment. The main objective of this project was to demonstrate that refractive optics for the Warm Dense Matter experiment could be fabricated from low Z materials, which would survive in the LCLS beam. We also wanted to gain familiarity with the LCLS so that LLNL experimenters would be better prepared to take advantage is of its capabilities. And finally, we wanted to understand how these technologies could be applied to programs within LLNL.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15009817
- Report Number(s):
- UCRL-TR-202967; TRN: US0406631
- Resource Relation:
- Other Information: PBD: 16 Mar 2004
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
BERYLLIUM
COHERENT RADIATION
COMPTON EFFECT
ENERGY DENSITY
FOCUSING
FREE ELECTRON LASERS
LAWRENCE LIVERMORE NATIONAL LABORATORY
LIGHT SOURCES
LINEAR ACCELERATORS
LITHIUM
MICROSCOPY
OPTICAL SYSTEMS
PHOTON BEAMS
STANFORD LINEAR ACCELERATOR CENTER
US NATIONAL IGNITION FACILITY
WIGGLER MAGNETS