Chirped pulse amplification in a seeded free-electron laser for generating high-power ultra-short radiation

In this paper, a proposal to generate intense ultra-short free-electron laser (FEL) pulses at Shanghai deep ultraviolet FEL (SDUV-FEL) by combining the chirped pulse amplification (CPA) technique with the high-gain harmonic generation (HGHG) technique is presented. In this proposal, a frequency chirped seed pulse obtained by stretching an ultra-short laser pulse is first used to create frequency-chirped bunching at the laser harmonics in an electron beam; then the frequency chirped harmonic radiation is amplified by an energy chirped electron beam; finally the output radiation pulse which inherits the properties of the seed pulse is compressed to provide an ultra-intense ultra-short radiation pulse. The feasibility and performance of this CPA-HGHG scheme are studied with start-to-end simulations using the parameters of SDUV-FEL. The effects of frequency chirped seed pulse on different stages of FEL gain in the radiator has been studied. It is found that the beam energy chirp is not necessary to generate frequency chirped pulse in the coherent harmonic generation (CHG) regime where a short radiator with bandwidth larger than or comparable to the seed pulse is used. This makes the CPA-CHG scheme well-suited for generating intense ultra-short radiation pulse in synchrotron light sources. On the other hand, a proper energy chirp to match the frequency chirp of the seed laser is critical in CPA-HGHG scheme where a long radiator is used. Using the beam parameters at SDUV-FEL as a representative example, we show that a frequency chirped UV pulse obtained via CPA-HGHG scheme can be compressed by over one order of magnitude by an optical pulse compressor. This technique has the potential of generating ultra-intense ultra-short XUV radiation pulses directly from a commercial infrared seed laser and may open new research opportunities for strong-field physics and ultrafast sciences. (c) 2013 Elsevier B.V. All rights reserved.