Possible enhancement of SASE FEL output field intensity induced by local phase jump

A possible influence on the FEL dynamics of a locally induced phase jump between the FEL radiation and electron beam is considered. A numerical study has been made for the SASE mode FEL supposing that the phase jumps are introduced at different depths inside the undulator. The FEL evolution starting from a small input signal was studied in 1D high gain approach. It was shown that the FEL radiation output is sensitive to the phase jump value if it is introduced at the depth where saturation of output power takes places. In the steady state regime, the phase displacement of order ∼π provides enhancement of the peak output power up to 50%. Some kind of optical tapering is also possible giving further FEL efficiency enhancement.