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Hollow-core negative-curvature fiber for UV guidance.

UV guiding fibers are highly sought after in laser and spectroscopy applications. Recent advances in hollow-core fiber orient a practical approach for proper UV light delivery sustainable to high-power and long-term irradiation. In this Letter, we report two types of hollow-core negative-curvature fibers (NCFs) in a UV spectral range. Their structures consist of one ring of six small (7.9 μm in diameter) and four big (20.8 μm in diameter) tubes, enclosing a hollow core of similar size (∼15  μm in diameter). The six-tube NCF shows an attenuation level of 0.13±0.01  dB/m at 300 nm. It is capable of delivering 20 ps, 160 μJ pulses at 355 nm with no damage to the fiber facet. The novel four-tube NCF exhibits an attenuation level of ∼0.3±0.15  dB/m at 355 nm. Its fundamental core mode is guided in an intentionally designed "cladding mode mismatching" region. This four-tube design possesses a high degree of down-scalability for deep-UV guidance and has the potential in attaining polarization-maintaining performance.