Sub-thermodynamic equilibrium surface roughness in hollowcore fibers for the ultraviolet range

International audience; We report on the development of new state-of-the-art ultralow-loss hollow-core fibers guiding in the short-wavelength range. The new record low attenuation values are as low as 50.0 dB/km at 290 nm, 9.7 dB/km at 369 nm, 5.0 dB/km at 480 nm, 0.9 dB/km at 558 nm, and 1.8 dB/km at 719 nm. Notably, the core roughness levels of the new state-of-the-art fibers are under the thermodynamic equilibrium limit set by the surface capillary waves scenario in amorphous silica.