STELLA-II: demonstration of monoenergetic laser acceleration

Monoenergetic laser acceleration of trapped microbunches has been demonstrated for the first time. An inverse free electron laser (IFEL) is used to create microbunches, which are then accelerated by a second IFEL using a tapered undulator. An adjustable magnetic field chicane is located between the two IFELs and is used to control the phase of the microbunches with respect to the laser field in the second IFEL. The IFELs are driven by a single laser beam from a high peak power CO/sub 2/ laser. During the experiment, the trapped portion of the microbunch electrons had an energy gain of < 16% with an energy width of /spl sim/ 0.86% (full width at half- maximum).