Abstract
In this paper, several schemes of soft X-ray and hard X-ray free electron lasers (XFEL) and their progress are reviewed. Self-amplified spontaneous emission (SASE) schemes, the high gain harmonic generation (HGHG) scheme and various enhancement schemes through seeding and beam manipulations are discussed, especially in view of the generation of attosecond X-ray pulses. Our recent work on the generation of attosecond hard X-ray pulses is also discussed. In our study, the enhanced SASE scheme is utilized, using electron beam parameters of an XFEL under construction at Pohang Accelerator Laboratory (PAL). Laser, chicane and electron beam parameters are optimized to generate an isolated attosecond hard X-ray pulse at 0.1 nm (12.4 keV). The simulations show that the manipulation of electron energy beam profile may lead to the generation of an isolated attosecond hard X-ray of 150 attosecond pulse at 0.1 nm.
Highlights
Synchrotron light sources have shown remarkable scientific capabilities and quite successfully reveal various scientific and technological phenomena in a wide range of materials, including semiconductors, polymers, ceramics and biological molecules
The energy modulation of an electron beam at a low energy is more convenient than at a high energy, because a longer wiggler is required at a higher energy. Another advantage of the energy modulation at a lower energy is the small energy spread induced in an electron beam by a wiggler magnet itself. This energy modulation at low energy was studied in combination with another successive accelerator, prior to entering into a long spontaneous emission (SASE) FEL undulator [35].The simulation resulted in the generation of X-ray pulses with a pulse width of ~200 attoseconds with a perfect synchronization to a modulating laser pulse
We demonstrate that an isolated attosecond X-ray pulse can be produced by manipulating electron beam energy distributions together with density modulation in an enhanced SASE scheme for a given laser wavelength
Summary
Synchrotron light sources have shown remarkable scientific capabilities and quite successfully reveal various scientific and technological phenomena in a wide range of materials, including semiconductors, polymers, ceramics and biological molecules. The current third-generation synchrotron light sources (3G SLSs) generate X-ray pulses in the picosecond time domain, which does not allow the study and the manipulation of ultrafast dynamics in atoms, molecules and nanoscopic systems. With the advent of XFEL, a new era of X-ray science has arrived; yet, the current XFEL is to be further developed to deliver attosecond pulse, with which real-time studies of electron-electron correlations, unexplored up to now, can be fully investigated. In this vein, this paper concerns the generation of attosecond hard X-ray pulses, including a review of current XFEL technologies.
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