In two- and three-dimensional imaging, radiation damage is a major concern. The intensities required to achieve an imaging resolution of 200 Å would kill live cells. Furthermore, the local heating of the object could alter its physical structure. Ideally, one would want to take a timed sequence of images in order to follow the microscopic details of biological processes in living cells. A potential solution to this problem would be to take a single-pulse flash picture. The high coherence and single-pulse energies of the proposed x-ray FEL may allow the simultaneous recording of a number of holographic images, and a 200-fs exposure time should be fast enough that the atoms vaporized in the imaging process will not have had time to move enough to blur the object at the 200-Å resolution.
Third-generation synchrotron sources, while not as bright or as coherent as an x-ray free electron laser, will provide far more intense and coherent radiation than is currently available. While many scientific studies using x-rays produced by an FEL appear to be possible, the feasibility of these studies should first be explored using third-generation synchrotron sources that are just beginning to operate. This exploration, in conjunction with further research and development of x-ray FEL technology, will provide the basis for an informed decision regarding possible future construction of an x-ray FEL facility.
Even if cost were not a factor, construction of an x-ray free electron laser would require significant research and development, particularly at the shorter wavelengths.
The costs and risks of building a free electron laser facility would be much higher in the x-ray region than in any other region, and the uncertainties in both the cost and the technology are also much higher.
Scientific opportunities and the use of coherence in the x-ray spectral region should be explored initially by the use of existing and planned synchrotron sources.
The research and development necessary for the possible construction of an x-ray free electron laser should be supported. The goals of this research and development should be improving the technology and lowering the cost.
Research and development on other advanced coherent x-ray sources should continue to be supported. One of the goals of this research and development should be the production of devices of appropriate size and cost to be useful for scientific research on a departmental or individual-investigator scale.
Construction of an x-ray free electron laser user facility should not be undertaken at the present time.