CERN Accelerating science

Article
Title	Theory of Coherent Radiation from a Grating-Waveguide Free-Electron Laser
Author(s)	Huang, Y C ; Lin, Y Y
Affiliation	(NTHU, Hsinchu)
Publication	2005
In:	27th International Conference on Free Electron Lasers, Palo Alto, CA, USA, 21 - 26 Aug 2005, pp.239
Subject category	Accelerators and Storage Rings
Abstract	A Smith-Purcell radiator produces transversely asymmetric radiation modes due to the arrangement of a grating on one side of the electron beam. This asymmetric output could limit the usefulness of such a device in the THz spectrum where diffraction of waves is severe. It is possible to produce symmetric radiation from a double-grating waveguide driven by an electron beam traversing the waveguide gap. We derive a theory that describes the modes and small signal gain of this novel grating-waveguide free-electron laser. Our theory shows that extremely high laser gain is obtained when the electron beam is phase matched to the middle or edge of the radiation bands where the radiation modes have zero group velocity. In our calculation we obtained 66dB/mm gain at 298 µm for a 5 mA, 30keV driving beam in a grating waveguide with a 50-micron, 40% duty-cycle grating period, a 60-micron groove depth, and a 150 micron waveguide gap. This extremely high gain indicates that this novel device establishes resonance without resonator mirrors in a one-dimensional photonic-crystal lattice or from distributed feedbacks in the grating pairs. Experimental progress will be reported in the conference.