Abstract
Many high-gain free electron lasers worldwide are planning to incorporate seeding setups into their day-to-day operation. These techniques provide both longitudinal and transverse coherence and extended control of the output free electron laser radiation spectral properties. However, the output wavelength and repetition rate strongly depend on the properties of the seed laser system. With the laser peak power required for successful seeded operation, it is currently not possible to increase their repetition rate to an extent that it matches the electron bunch repetition rate of superconducting accelerators. Here, we investigate the advantages of a modification of standard seeding setups, by combining the seeding with the so-called optical klystron. With this new seeding setup, it is possible to decrease the seed laser power requirements and therefore, seed laser systems can increase their repetition rate at the same wavelength. We show simulation results in a high-gain harmonic generation (HGHG) setup for a range of harmonics (8th to 15th) and we verify the reduction of seed laser power required with an Optical Klystron HGHG scheme. Finally, we comment on the stability of the proposed setup to jitter sources and to shot-to-shot fluctuations and compare to the standard HGHG scheme.
Highlights
High-gain free electron lasers (FELs) have been delivering light characterized by high brightness and wavelength tunability to user experiments for more than a decade [1,2]
We show simulation results in a high-gain harmonic generation (HGHG) setup for a range of harmonics (8th to 15th) and we verify the reduction of seed laser power required with an Optical Klystron HGHG scheme
We show that even with a lowseed laser power it is possible to preserve the coherence of the output FEL on a shot-to-shot basis, significantly extending the previously reported results [42]
Summary
High-gain free electron lasers (FELs) have been delivering light characterized by high brightness and wavelength tunability to user experiments for more than a decade [1,2]. The oscillator can be used either as part of a multistage scheme that is combined with harmonic conversion [7,8,9,10] or as a direct source of radiation The latter oscillator FELs are based on x-ray cavities which provide short wavelengths with full coherence and high repetition rate [11,12,13,14,15,16]. Self-amplified spontaneous emission (SASE) [17] is one of the standard methods in high-gain FELs to deliver light to experiments It offers a wide range of wavelength tunability down to hard x rays [18,19,20,21] and with high repetition rate [2,4], but it suffers from intrinsic limitations. We discuss the impact of the lower signal to noise ratio on the shot-to-shot stability
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