UCLA, Los Angeles, USA
The Self Amplified Spontaneous Emission (SASE) operation of high-gain Free Electron Lasers (FELs) allows for amplification from "noise" when no suitable seed sources are available. While SASE FELs can achieve high powers and short radiation pulses within the X-ray region, they are hindered by large linewidths and fluctuations in amplitude and temporal profiles. Various approaches have been proposed to "clean up" the spontaneous emission and produce better effective seed signals. This paper presents the use of monocapillary X-ray optics as an alternative to current methods to improve SASE operation. A monocapillary tube placed at the beginning stages of the undulator can reduce the bandwidth and enhance a narrow band of the spontaneous emission amplified by the FEL. Monocapillary tubes guide radiation due to total external reflection, and the critical angle of the guiding is dependent on the frequency of the radiation (and indirectly on the surface profile and materials).
