Steady-state microbunching in a storage ring at EUV wavelengths
In plain words
If electrons in a storage ring stayed bunched into slices a few nanometers long on every turn, they would emit strong coherent ultraviolet light continuously; only the first step of this scheme has been shown.
Precise statement
Steady-state microbunching (SSMB) uses laser modulators for longitudinal focusing in a low-momentum-compaction ring so that electrons stay in optical-scale microbunches turn after turn; retention of laser-induced microbunching at a $1.064e-4\,\mathrm{cm}$ wavelength over successive turns was reported at the Metrology Light Source, Berlin, in 2021 (Deng et al., https://doi.org/10.1038/s41586-021-03203-0). Determine whether a ring can hold microbunches of rms length below $\sim 2e-7\,\mathrm{cm}$ in steady state, with quantum excitation, intrabeam scattering and laser phase noise included, giving coherent radiation at $1.35e-6\,\mathrm{cm}$ ($13.5\,\mathrm{nm}$) with average power near $1e10\,\mathrm{erg}/\mathrm{s}$.
What would settle it
Measured steady-state coherent emission at the target wavelength whose power scales as the square of the number of electrons per microbunch.
Status in the literature
Unverified note
INSPIRE records through 2026 show proof-of-principle work at the Metrology Light Source and ring design studies, with no steady-state operation reported.