Soft X-Ray Stimulated Bremsstrahlung In Traveling Longitudinal Electric Wake-Fields Of Two-Beam Pill-Box Cavities

The amplification of laser light in a free electron laser (FEL) due to stimulated bremsstrahlung in a traveling longitudinal undulating electric field is derived. It is shown that this FEL provides sufficient gain to be used as a coherent radiation source down to the soft x-ray regime. It is suggested that, among other possibilities, the wake-field produced in a two-beam elliptical or annular pill-box cavity is suitable for the required traveling longitudinal undulating electric field.