Characterization of ultraviolet femtosecond pulse propagation in aluminum-coated capillary fibers

We demonstrate that hollow core fibers with aluminum-coated bores of φ=0.7 mm and φ=1.0 mm are well suited for guiding high-power ultraviolet femtosecond pulses. We consider 1-m -long fibers in two geometries: straight and bent with a 30-cm radius of curvature. The straight fibers transmit approximately 60% of the power at 200 nm and 85% at 266 nm, while the corresponding numbers for the bent fibers are 25% and 35%. The duration of the femtosecond pulses increases by 10% and 50% per meter at 200 and 266 nm, respectively. The broadening increases to a factor of two when the fiber is bent. The maximum transmitted pulse energy at 266 nm is 100 μJ corresponding to 0.5 GW or an intensity of 1011 W cm2. However, this value is limited only by the 266 nm pulse generation and is expected to go even higher. The applicability of the powerful femtosecond pulses from the fiber is demonstrated by an experiment in which water is ionized by two-photon absorption. This experiment indicates the potential of using aluminized hollow core fibers in medical therapy with ultraviolet femtosecond pulses.