High-efficiency ultraviolet generation in a resonance-free anti-resonant hollow-core fiber

We report the first demonstration of high-efficiency ultraviolet (UV) pulse generation in a resonance-free anti-resonant hollow-core fiber (AR-HCF). Using the wet-etching technique, we successfully reduced the cladding-tube wall thickness of the AR-HCF to 115 nm, thereby eliminating all cladding-induced structural resonances between the near-infrared pump and the deep UV wavelengths. This structural modification fundamentally suppresses competing conversion to other phase-matching points induced by structural resonances and mitigates the pump spectral broadening limitation, achieving a UV conversion efficiency as high as 12%—twice that of previous demonstrations in gas-filled AR-HCFs. This UV conversion efficiency is comparable to that of meter-scale gas-filled capillaries that require pump pulse energy of hundreds of microjoules while also maintaining the AR-HCF’s inherent advantages of centimeter-scale compactness and low pump energy at the few microjoule level.