The ability to deliver high energy and high average power laser radiation through a flexible fiber is a key enabler for numerous processing applications. This provides better space management, direct delivery to the processing area and better serviceability. Silica fibers were successfully used to deliver signals in the near-infrared and visible spectra, but they suffer notably from high absorption in the UV region. Hollow-core fibers alleviates this issue as the mode of propagation minimally overlaps with the surrounding guiding microstructure. However, their power scaling was currently limited by two factors: beam quality/stability of available UV sources and power handling of the thin capillary microstructure, especially due to the limited control of the internal surface roughness.
In this work we will present recent results achieved by the combination of a high beam quality UV nanosecond lasers and low-internal roughness hollow-core fibers to achieve efficient UV fiber delivery. After giving experimental characterizations of the improved hollow-core fiber, we will detail the characterization of the 343nm UV source, including beam stability measurements at full power and evolution of beam quality on a large range of parameters. Fiber delivery with power above 20W (150 µJ energy) and transmission above 90% will be presented. We will also present preliminary results achieved at 266 nm with output power of 20.5mW (20.5 µJ) and transmission efficiency above 90%.