Theoretical proposal for a unidirectional optical amplifier

The possibility of achieving a unidirectional optical amplifier is theoretically predicted with a model in the vacuum environment. The operation of this amplifier is based on the transfer of the kinetic energy of an electron beam to an optical one where both are propagating in the same direction. The optical beam propagates in a dielectric waveguide where it partly penetrates into the vacuum in the form of an evanescent wave. The electron beam is emitted from an electron gun and propagates along the surface of the dielectric waveguide, exciting the optical beam. The propagation speed of the optical beam is slowed down with the aid of the dielectric waveguide and is made to coincide with that of the electron beam. Quantum mechanical analysis of the interaction between the optical beam and the electron beam is given, based on the density matrix formalism. At the wavelength of 0.5 /spl mu/m, the gain coefficient is calculated to be about 12 cm/sup -1/ under the excitation voltage of 64 kV and the electron beam current of several microamperes.