Abstract: The invention involves a free electron laser having reduced sensitivity to variations in the energy of the input electrons. This effect is achieved by first laterally dispersing the electrons in accordance with their energies and thereafter injecting the dispersed electrons with angular and/or lateral variations to alternate polarity deflecting means.

Abstract: A method and apparatus for constructing a continuous wave (CW) free elect laser (FEL) system capable of providing tunable high power laser radiation at short wavelengths using low-energy recirculating DC electron beams. This method replaces the static periodic magnetic field used in conventional FEL systems with an equivalently intense and continuous electromagnetic pump field having spatial periodicity less than 1 cm. The pump field is generated by a low-energy recirculated DC electron beam interacting with a transverse static periodic magnetic field.

Abstract: An apparatus and method is described for greatly enhancing the power output f a free electron laser. To enhance the electron kinetic energy that is converted to laser radiation, the wave amplification resonance condition is continuously changed along the length of the laser interaction region. The changing resonance condition is achieved by use of a static magnetic field transverse to the injected electron beam, the magnetic field having a longitudinal magnetic field gradient.

Abstract: Improved gain and the elimination of beam insertion and extraction compensation in free electron lasers is realized by means of a helical periodic magnet. The magnet comprises one or more layers of coaxial bifilar helical conductors each being 180.degree. displaced and conducting current in opposite directions. The end portions of the magnet are tapered by extending successive layers one or more turns to provide a field gradient that uniformly decreases to zero.