Generation of Coherent Monochromatic Betatron Radiation by Laser-triggered Ionization Injection in Plasma Accelerators

Betatron radiation, emitted from the relativistic electrons in plasma accelerators, is generally incoherent and broadband. However, if the electron beam has a coherent structure, it has the potential to emit coherent betatron radiation. In this paper, we show that coherent monochromatic betatron radiation can be emitted from the nano-bunched electron beams generated by laser-triggered ionization injection in plasma wakefield accelerators. Donut-like coherent monochromatic betatron radiation (~5 eV) without orbital angular momentum is generated by use of a linearly polarized laser, while coherent monochromatic betatron radiation (~ 10 e V) with orbital angular momentum can be potentially produced by use of a circularly polarized laser.