Abstract
The resolution in x-ray coherent diffractive imaging applications can be improved by increasing the number of photons in the optical pulse. An x-ray free-electron laser (XFEL) producing pulses with terawatt (TW) peak power and about 10 femtosecond duration can satisfy this requirement. In this paper, we consider the conditions necessary for achieving powers in excess of 1 TW in a 1.5 Å FEL. Using the MINERVA simulation code, an extensive steady-state analysis has been conducted using a variety of undulator and focusing configurations. In particular, strong focusing using FODO lattices is compared with the natural, weak focusing inherent in helical undulators. It is found that the most important requirement to reach TW powers is extreme transverse compression of the electron beam in a strong FODO lattice in conjunction with a tapered undulator. We find that when the current density reaches extremely high levels, that the characteristic growth length in the tapered undulator becomes shorter than the Rayleigh range giving rise to optical guiding. We also show that planar undulators can reach near-TW power levels. In addition, preliminary time-dependent simulations are also discussed and show that TW power levels can be achieved both for self-seeding and pure self-amplified spontaneous emission. This result shows that high-resolution, single molecule diffractive imaging may be realized using XFELs.
Highlights
The number of x-ray free-electron lasers (XFELs) is increasing around the world [1,2,3,4,5,6,7] to service a fast-growing user community
The physics underlying efficiency enhancement in tapered undulators has been understood for decades [19,20,21]; tapered undulator experiments have historically shown enhancements in the efficiency over the saturated power in a uniform undulator of less than five [22,23,24]
We have examined the effect of extreme focusing on the performance of tapered undulator XFELs using the MINERVA simulation code and found that enhancements over the saturated power in a uniform undulator by a factor of 50–100 are possible
Summary
It is found that the most important requirement to reach TW powers is extreme transverse compression of the electron beam in a strong. We find that when the current density reaches extremely high levels, that the characteristic growth length in the tapered undulator becomes shorter than the Rayleigh range giving rise to optical guiding. We show that planar undulators can reach near-TW power levels. Preliminary time-dependent simulations are discussed and show that TW power levels can be achieved both for self-seeding and pure self-amplified spontaneous emission. This result shows that high-resolution, single molecule diffractive imaging may be realized using XFELs
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