Short wavelength seeding through compression for free electron lasers

In this paper, we propose a seeding scheme that compresses an initial laser modulation in the longitudinal phase space of an electron beam by using two opposite sign bunch compressors and two opposite sign energy chirpers. This scheme could potentially reduce the initial modulation wavelength by a factor of C and increase the energy modulation amplitude by a factor of C, where C is the compression factor of the first bunch compressor. Using two lasers as energy chirpers, such a modulation compression scheme can generate kilo-Amper short wavelength current modulation with significant bunching factor from an initial a few tens Amper current. This compression scheme can also be used to generate a prebunched single atto-second short wavelength current modulation and prebunched two color, two atto-second modulations.