Abstract
As a new-generation light source, free-electron lasers (FELs) provide high-brightness X-ray pulses at the angstrom-femtosecond space and time scales. The fundamental physics behind the FEL is the interaction between an electromagnetic wave and a relativistic electron beam in an undulator, which consists of hundreds or thousands of dipole magnets with an alternating magnetic field. Here, we report the first observation of the laser-beam interaction in a pure dipole magnet, in which the electron beam energy modulation with 40-keV amplitude and 266-nm period is measured. We demonstrate that such an energy modulation can be used to launch a seeded FEL, that is, lasing at the sixth harmonic of the seed laser in a high-gain harmonic generation scheme. The results reveal the most basic process of the FEL lasing and open up a new direction for the study and exploitation of laser-beam interactions.
Highlights
A charged particle radiating energy in the form of an electromagnetic wave when it is accelerated is the basic principle behind modern accelerator-based light sources
We explored the feasibility of using the energy modulation obtained in the dipole magnet for free-electron lasers (FELs) lasing at the sixth harmonic of the seed laser
We have demonstrated and measured the interaction between a laser and relativistic electrons in a pure dipole magnetic field
Summary
A charged particle radiating energy in the form of an electromagnetic wave when it is accelerated is the basic principle behind modern accelerator-based light sources Among such sources, synchrotron radiation and free-electron lasers (FELs) have played key roles in numerous scientific fields by providing high-brightness electromagnetic waves over a wide spectral range. More advanced seeded FEL schemes are being developed to improve the frequency multiplication efficiency.[10,11,12] In addition, a laser heater[13,14] is normally placed before the bunch compressor in the linac section of an x-ray FEL facility, where an external laser is employed to interact with the electron beam, thereby increasing the uncorrelated beam energy spread and suppressing the microbunching instability induced by the effects of the longitudinal space charge and coherent synchrotron radiation. The feasibility of seeded FEL lasing using such energy modulation was demonstrated
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