Compact free-electron lasers using laser driven cascaded dielectric nano-pillar arrays

We proposed a concept of very compact free-electron lasers (FELs) using infrared lasers to drive cascaded dielectric nano-pillar arrays (DNPAs). It employs a preset section of DNPA, driven by the longitudinal polarized laser, to prebunch the electron beam via the longitudinal velocity bunching mechanism. After drifting a certain distance, these electron bunches then enter the downstream cascaded sections of DNPA, which are alternately driven by transverse polarized lasers with phase shift of \pmbπ. The electron bunches will wiggle synchronously (due to the deflecting forces exerted by the transverse polarized electric fields) in these DNPAs, which act as effective undulator in conventional FELs. By changing the length of these sections, the undulator periodicity, together with the undulator strength K-value, can be adjusted effectively. It sets a prototype to develop the ultraviolet and soft X-ray FELs with tabletop sizes.