Wavelength Scaling and Multi-Color Operation of a Plasma Driven Attosecond X-ray Source Via Harmonic Generation

The generation of high power coherent soft X-ray pulses of sub-100 asduration and 10 nm wavelength using beams from a GeV energy plasma wakefieldaccelerator has been recently investigated in Ref. [arXiv:2011.07163]. As afuture upgrade to this concept, this contribution investigates scaling toshorter X-ray wavelengths by cascading undulators tuned to higher harmonics ofthe fundamental. We present two simulation studies for plasma-driven attosecondharmonic generation schemes with final photon wavelengths of 2 nm and 0.40 nm.We demonstrate in these schemes that using undulators with retuned fundamentalfrequencies can produce GW-scale pulses of sub-nm radiation with tens ofattosecond-scale pulse lengths, an order of magnitude shorter than currentstate-of-the-art attosecond XFELs. This multi-pulse multi-color operation willbe broadly applicable to attosecond pump-probe experiments.