Control and application of beam microbunching in high brightness linac-driven free electron lasers

We review physical mechanisms and driving forces behind the microbunching instability in modern free-electron lasers. Laser heater and alternative methods to fight the instability are presented and evaluated. Advanced uses of the laser heater setup for temporal and spectral controls of the FEL and for intense THz production are discussed. A recent idea of using the microbunching instability for coherent generation of UV radiation is described. Noise suppression in relativistic beams is briefly reviewed.