WAVEFRONT CONTROL
FOCUS
developed to measure flying focus propagation directly within the plasma medium. Ultimately, combining the flying focus with laser post-compression to deliver the shortest possible pulses will be key to maximizing performance, as electron energy gain scales with the inverse square of the pulse duration.
Figure 3. Simulation of a flying focus beam( red) propagating in a plasma( greyscale).
of an ultra-high-intensity flying focus and its application to wakefield acceleration [ 6,7 ]. Unlocking the full potential of this technique will require three key developments. First, a deeper understanding of laser-plasma dynamics is essential, as PIC simulations indicate that the plasma can strongly distort the flying focus under certain conditions. Second, new optical techniques are needed to finely control RGD at high laser powers. Third, because characterizations to date have been conducted almost entirely in vacuum, innovative diagnostics must be
CONCLUSION Structuring a laser pulse in space and time enables to turn the velocity of its intensity peak into a free parameter, tunable from subluminal to superluminal and set independently of how the light itself propagates. Applied to laser-wakefield acceleration, a flying focus travelling at exactly c in plasma keeps the accelerated electrons locked in the accelerating phase of the wake for as long as fresh light continues to feed it, removing the limits of dephasing, depletion, and diffraction altogether. Simulations already show a marked gain in electron energy for a given laser energy, and the scaling with laser power suggests that multi-petawatt facilities could push this scheme to several tens, or even a hundred, GeV in a single stage.
More broadly, flying focus and structured light decouple the local properties of a laser ' s focus( position, timing, intensity etc.) from its overall propagation. This opens new degrees of freedom for ultra-intense laser-plasma experiments. Beyond dephasingless LWFA, this promises applications in laser-driven light sources, ion acceleration, and quantum electrodynamics studies.
REFERENCES
[ 1 ] T. Tajima et J. M. Dawson, Phys. Rev. Lett. 43, 267( 1979)
[ 2 ] A. Sainte-Marie, O. Gobert et F. Quéré, Optica 4, 1298( 2017); D. H. Froula et al., Nat. Photonics 12, 262( 2018)
[ 3 ] S. Smartsev et al., Opt. Lett. 44, 3414( 2019)
[ 4 ] Caizergues et al., Nat. Photonics 14, 475( 2020); J. P. Palastro et al., Phys. Rev. Lett. 124, 134802( 2020)
[ 5 ] A. Picksley et al., Phys. Rev. Lett. 133, 255001( 2024) [ 6 ] A. Lieberman et al., Phys. Rev. Research 8, L022001( 2026) [ 7 ] C. Arrowsmith et al., Nat. Phys. 22, 1513( 2026)
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