Tunable coherent radiation in the soft X-ray and extremeultraviolet spectral regions
Attwood, D.T.; Naulleau, P.; Goldberg, K.A.; Tejnil, E.; Chang Chang; Beguiristain, R.; Batson, P.; Bokor, J.; Gullikson, E.M.; Koike, M.; Medecki, H.; Underwood, J.H.
Quantum Electronics, IEEE Journal of
Volume 35, Issue 5, May 1999 Page(s):709 - 720
Digital Object Identifier 10.1109/3.760317
Summary:Undulator radiation, generated by relativistic electrons
traversing a periodic magnet structure, can provide a continuously
tunable source of very bright and partially coherent radiation in the
extreme ultraviolet (EUV), soft X-ray (SXR), and X-ray regions of the
electromagnetic spectrum. Typically, 1-10 W are radiated within a 1/N
relative spectral bandwidth, where N is of order 100. Monochromators are
frequently used to narrow the spectral bandwidth and increase the
longitudinal coherence length, albeit with a more than proportionate
loss of power. Pinhole spatial filtering is employed to provide
spatially coherent radiation at a power level determined by the
wavelength, electron beam, and undulator parameters. In this paper,
experiments are described in which broadly tunable, spatially coherent
power is generated at EUV and soft X-ray wavelengths extending from
about 3 to 16 nm (80-430-eV photon energies). Spatially coherent power
of order 10 μW is achieved in a relative spectral bandwidth of
9×10-4, with 1.90-GeV electrons traversing an 8-cm
period undulator of 55 periods. This radiation has been used in 13.4-nm
interferometric tests that achieve an rms wavefront error (departure
from sphericity) of λeuv/330. These techniques scale
in a straightforward manner to shorter soft X-ray wavelengths using
4-5-cm period undulators at 1.90 GeV and to X-ray wavelengths of order
0.1 nm using higher energy (6-8 GeV) electron beams at other facilities
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