Paper TF-ThP14
Fabrication of High-period-number Resonant Transition Radiation Emitters for Generation of Femto-second Hard X-rays

Thursday, November 2, 2017, 6:30 pm, Room Central Hall

Femtosecond resonant transition radiation (RTR) in x-ray region can be generated from alternatingly stacked multilayer structures when they are driven by relativistic ultrashort electron beams. In contrast to large-scale facility like x-ray free electron lasers (XFELs), compact x-ray sources of moderate peak brightness can be developed by using this method for some ultrafast scientific research. These structures can be fabricated by coating layer pairs of high and low density materials. Narrow-bandwidth x-rays can be generated by increasing the number of periods (i.e. the number of layer pairs). Thanks to the high transmittance of hard x-ray in most materials, the radiation bandwidth is not limited by x-ray absorption up to dozens or even hundreds of layers. In this report, we present our efforts on the development of a femtosecond narrow-band 12 keV x-ray source by driving high-period-number RTR emitters with the NSRRC photoinjector linac system which is operating in short bunch mode. Since the optimum thickness for one emitter period is of several hundred nanometers, total thickness of an emitter can be as thick as few tens of μm. Sputtering is considered as an appropriate process to fabricate these structures with reliable quality in reasonable time. The fabrication process of making such emitters that are composed of Mo/Si multilayers is under test. Structures of 60 periods (120 layers) have been fabricated. The estimated photon yield is about 3x10⁴ for a 100 pC drive beam. A portion of x-ray generated from multi-layer structure would be absorbed by the Si substrate of the emitter, so removing the substrate would be helpful to enhance photon flux. The process to remove the substrate is also discussed.

Acknowledgement

Work supported by the Ministry of Science and Technology, ROC (Taiwan).