| 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 (CW) molecular laser has been demonstrated. A linear relationship between FEL output power and seeding power is obtained for short FEL pulses, demonstrating considerable power gain together with a 30% reduction in laser start-up time. The pulse to pulse frequency bandwidth was reduced by one order of magnitude, from 1.6GHz to 0.16GHz and an order of magnitude reduction of the side-band mode beating was observed in a single pulse. Numerical simulations of the multimode FEL problem shows that in normal operation of the UCSB FEL side-band mode suppression is rather slow, underlining the importance of seeding to obtain single mode operation for the available pulse length. |
