Abstract
Aiming for the future upgrade of a hard x-ray beamline at the Pohang accelerator laboratory x-ray free-electron laser (PAL-XFEL), we first analyze the scheme recently proposed for the attosecond-terawatt (TW) x-ray pulse [Phys. Rev. Lett. 110, 084801 (2013) [CrossRef] ]. An x-ray pulse with 32 attosecond full-width half maximum (FWHM) pulse duration and in power is shown in simulations using the PAL-XFEL parameters. Furthermore, to remove neighboring radiation pulses and to generate an isolated attosecond-TW x-ray pulse, the role of optical laser frequency chirp is examined on the electron beam current modulation as well as on the x-ray pulse generation in the undulator. Our simulations show an isolated x-ray pulse with 42 attosecond FWHM pulse duration and in power for the optimal frequency chirp of a 400 nm optical laser. Recently, in a simpler method [J. Synchrotron Radiat. 23, 1273 (2016) [CrossRef] ] and [Phys. Rev. ST Accel. Beams 8, 040701 (2005) [CrossRef] ], using a frequency-chirped optical laser and the electron beam delays in between undulator sections, it has been reported that an isolated attosecond-TW x-ray pulse can be obtained at the undulator end. For optimal chirp in this simple setup, we show 50 attosecond FWHM pulse duration and in power with photons per pulse at 0.1 nm radiation wavelength. Generation of such inherently synchronized, powerful single attosecond x-ray pulses at PAL-XFEL will be advantageous to the pump-probe experiments in the study of ultrafast dynamics.
© 2018 Optical Society of America
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