Optical wakefield from a photonic bandgap fiber accelerator

Photonic Bandgap (PBG) structures have recently been proposed as optical accelerators for their high coupling impedance and high damage threshold. As a first step in preparing a PBG accelerator, we propose to observe the optical wakefield induced by an electron beam traversing the structure in the absence of a coupled laser pulse. The electrons are focused into the fiber via a permanent magnet quadrupole triplet. The electrons excite fiber modes with speed-of-light (SOL) phase velocities. By observing the wakefield using a spectrometer, the SOL mode frequencies are determined.