X-ray free-electron lasing in a flying-focus undulator

doi:10.1038/s42005-025-02028-x

X-ray free-electron lasing in a flying-focus undulator

2025-03-23

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DOI：10.1038/s42005-025-02028-x

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Laser-driven free-electron lasers (LDFELs) replace magnetostatic undulators with the electromagnetic fields of a laser pulse. Because the undulator period is half the wavelength of the laser pulse, LDFELs can amplify X rays using lower electron energies and over shorter interaction lengths than a traditional free-electron laser. In LDFELs driven by conventional laser pulses, the undulator uniformity required for high gain necessitates large laser-pulse energies. Here, we show that a flying-focus pulse provides the undulator uniformity required to reach high gain with a substantially lower energy than a conventional pulse. The flying-focus pulse features an intensity peak that travels in the opposite direction of its phase fronts. This enables an LDFEL configuration where an electron beam collides head-on with the phase fronts and experiences a near-constant undulator strength as it co-propagates with the intensity peak. Three-dimensional simulations of this configuration demonstrate the generation of megawatts of coherent X-ray radiation with 20 x less energy than a conventional laser pulse.

Keywords:

THOMSON SCATTERING

LASER

INTENSITY

VACUUM

VELOCITY

PLASMA

FEL

X-ray free-electron lasing in a flying-focus undulator

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