Bandwidth narrowing of the UCSB FEL by injection seeding with a cw laser

Narrow bandwidth operation of a free electron laser (FEL) at the University of California at Santa Barbara (UCSB) by seed injection from an external continuous wave molecular laser has been demonstrated. The pulse-to-pulse frequency bandwidth was reduced by one order of magnitude, from 1.6 to 0.16 GHz and an order of magnitude reduction of the sideband mode beating was observed in a single pulse together with a 30% reduction in laser startup time. Numerical simulations of the multimode FEL show that in normal operation of the UCSB FEL sideband mode suppression is rather slow underlining the importance of seeding to obtain single-mode operation for the available pulse length.