Attosecond pulse shaping using a seeded free electron laser
Attosecond pulses are central to the investigation of valence and core electron dynamics on their natural timescales 1 3 The reproducible generation and characterization of attosecond waveforms has been demonstrated so far only through the process of high order harmonic generation 4 7 Several methods for shaping attosecond waveforms have been proposed, including the use of metallic filters 8 9 multilayer mirrors 10 and manipulation of the driving field 11 However, none of these approaches allows the flexible manipulation of the temporal characteristics of the attosecond waveforms, and they suffer from the low conversion efficiency of the high order harmonic generation process. Free electron lasers, by contrast, deliver femtosecond, extreme ultraviolet and X ray pulses with energies ranging from tens of microjoules to a few millijoules 12 13 Recent experiments have shown that they can generate subfemtosecond spikes, but with temporal characteristics that change shot to shot 14 16 Here we report reproducible generation of high energy (microjoule level) attosecond waveforms using a seeded free electron laser 17 We demonstrate amplitude and phase manipulation of the harmonic components of an attosecond pulse train in combination with an approach for its temporal reconstruction. The results presented here open the way to performing attosecond time resolved experiments with free electron lasers. Generation of intense attosecond waveforms with independently controllable amplitude and phase is performed by using a seeded free electron laser.
Nature