s Re a

uate h le resonator mirrors. A simulation method is used that includes the dynamics of this rapidly focusing optical mode and the macroscopic and microscopic electron evolution. The amplitude and phase of the optical fields are represented by a short Rayleigh length resonator can be used to reduce the optical intensity on the mirrors. the rapid diffraction of the laser beam. Thousands of sample electrons interact with the laser field in 2. The optical mode resonator output coupling an 1=Qn: Higher-order modes have little impact on the far-field ARTICLE IN PRESSthe middle of the rapidly diffracting wave front. The simulation method can be used over a wide limit and the FEL interaction. The optical electric field in the fundamental mode [1] is Eðr; zÞ E0ðlZ0=AÞ 1=2 eiðkzotþfÞexpðpr2=A