Abstract
In this paper we present a high-gain free-electron-laser (FEL) oscillator scheme composed of two oscillators that are ideally coupled unidirectionally, with the coupled signal power flowing from the master to the amplifier oscillator. Electron bunches driving the oscillators are in perfect synchronization with the optical pulses building up within the respective cavities. The scheme is applied to a 100 MeV range superconducting energy recovery linac FEL. The computed mJ level, ultrashort pulse ($l10\text{ }\text{ }\mathrm{cycles}$) output in the midinfrared region indicates the potential of the proposed FEL oscillator scheme in driving up-frequency conversion processes in the x-ray region, enabling tunable, high average brightness, attosecond scale coherent soft/hard x-ray sources.
Highlights
In the quest for producing tunable, coherent x-ray pulses with femtosecond to attosecond scale durations, high-gain free-electron lasers based on self-amplified spontaneous emission (SASE) and harmonic generation schemes emerged in recent years as the prime candidates to realize powerful x-ray sources covering a spectral range from hundreds of eV to multiple keV photon energies
The design concepts of these x-ray free-electron-lasers (FELs) benefit significantly from the recent progresses made in the generation and transport of ultrashort, high brightness electron bunches in conjunction with the advances made in the conventional laser technology in the production of intense, a few-cycle long, low jitter, carrier-envelope phase stabilized optical pulses [1]
In this paper we present a step further towards achieving a significant enhancement [21] [several orders of magnitude compared to the current status (Refs. [8,9])] in the average brightness of the coherent, attosecond x-ray pulses generated by the mentioned up-frequency conversion processes
Summary
In the quest for producing tunable, coherent x-ray pulses with femtosecond to attosecond scale durations, high-gain free-electron lasers based on self-amplified spontaneous emission (SASE) and harmonic generation schemes emerged in recent years as the prime candidates to realize powerful x-ray sources covering a spectral range from hundreds of eV to multiple keV photon energies. Currently used OPA crystals set limitations to extend the above-mentioned performance beyond $4 m It will be a paramount challenge for the coming years to scale the available average power up to 2 orders of magnitude higher values (or more) with the aim to generate few-cycle long mid-IR pulses at megahertz (or higher) repetition rates while sustaining multi-mJ pulse energies; a key route in enhancing the average brightness of phasematched HHG emitted (soft/hard) x-ray photons orders of magnitude for a class of applications that require high average flux while high peak power is not desired. (Note that, once the former is demonstrated, the latter can be applied to produce even more energetic pulses with moderate enhancement factors of $50 to 100 opening up additional range of strong field applications.) The high repetition rate of the intense mid-IR pulses translates through the up-frequency conversion processes (HHG, XPA) into a high average brightness, attosecond soft/hard x-ray source, tunable (including all generated harmonics) within a spectral range that spans over hundreds of eV to multiple keV photon energies. In the case of the phasematched HHG in the keV region, the expected photon flux at cutoff energies scales to 1013–1014 ph= sec (within 1.0% BW) for 10 MHz operational frequency of the driver FEL
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