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We report on the generation of a three-octave-wide supercontinuum extending from the vacuum ultraviolet (VUV) to the near infrared, spanning at least 113-1000 nm (i.e., 11-1.2eV), in He-filled hollow-core kagome-style photonic crystal fiber. Numerical simulations confirm that the main mechanism is an interaction between dispersive-wave emission and plasma-induced blue-shifted soliton recompression around the fiber zero dispersion frequency. The VUV part of the supercontinuum, the modeling of which proves to be coherent and possesses a simple phase structure, has sufficient bandwidth to support single-cycle pulses of 500 asec duration. We also demonstrate, in the same system, the generation of narrower-band VUV pulses through dispersive-wave emission, tunable from 120 to 200 nm with efficiencies exceeding 1% and VUV pulse energies in excess of 50 nJ

Transmission of UV light with high beam quality and pointing stability is desirable for many experiments in atomic, molecular and optical physics. In particular, laser cooling and coherent manipulation of trapped ions with transitions in the UV require stable, single-mode light delivery. Transmitting even ~2 mW CW light at 280 nm through silica solid-core fibers has previously been found to cause transmission degradation after just a few hours due to optical damage. We show that photonic crystal fiber of the kagomé type can be used for effectively single-mode transmission with acceptable loss and bending sensitivity. No transmission degradation was observed even after >100 hours of operation with 15 mW CW input power. In addition it is shown that implementation of the fiber in a trapped ion experiment significantly increases the coherence times of the internal state transfer due to an increase in beam pointing stability. IntroductionStandard solid-core silica optical fibers are ideal for low-loss delivery of singletransverse-mode beams from the visible to the infrared spectral range. There are, however, a number of applications in which single-mode delivery of ultraviolet (UV) light by fiber would be highly desirable. For example, experiments on coherent manipulation of trapped ions for precision spectroscopy and optical clocks [1-6], quantum information processing [7,8] and trapped ion simulators [9,10] all require good beam quality and pointing stability, which is normally precisely what single-mode optical fibers can provide. For these applications a loss of a few dB/m is acceptable so long as the transmission remains single-mode and stable over time. A number of problems arise, however, when using standard optical fibers in the UV. Although single-mode guidance can be maintained (for the same core-cladding index step) simply by reducing the core diameter by the ratio of the wavelengths, or by using an endlessly single-mode solid-core photonic crystal fiber (PCF), most glasses become highly absorbing in the UV, and furthermore the transmission degrades over time due to UV-induced color center formation and optical damage in the core. For example, Yamamoto et al. found that in a PCF with a solid silica core the transmission dropped by more than 90% after ~4 hours when using 3 mW CW light at 250 nm [11].Recent experiments on nonlinear spectral broadening in gas-filled hollow core kagomé-style PCF have shown that these fibers are able to guide ultrashort pulses of UV light with losses of order 3 dB/m [12] and single-mode beam quality at average powers of ~50 µW [13]. Finite element simulations indicate that the light-in-glass fraction in kagomé-PCF is typically <0.01%, which circumvents the problem of UV-induced longterm damage in the glass. Kagomé-PCF can also be made effectively single-mode by decreasing the core size until higher-order modes have significantly higher propagation losses than the fundamental mode. A kagomé-PCF with 2 dB/m loss at 355 nm was recently demonstrated, but due to the rel...

Ultrafast broadband ultraviolet radiation is of importance in spectroscopy and photochemistry, since high photon energies enable single-photon excitations and ultrashort pulses allow time-resolved studies. Here we report the use of gas-filled hollow-core photonic crystal fibers (HC-PCFs) for efficient ultrafast nonlinear optics in the ultraviolet. Soliton self-compression of 400 nm pulses of (unprecedentedly low) ~500 nJ energies down to sub-6-fs durations is achieved, as well as resonant emission of tunable dispersive waves from these solitons. In addition, we discuss the generation of a flat supercontinuum extending from the deep ultraviolet to the visible in a hydrogen-filled HC-PCF. Comparisons with argon-filled fibers show that the enhanced Raman gain at high frequencies makes the hydrogen system more efficient. As HC-PCF technology develops, we expect these fiber-based ultraviolet sources to lead to new applications.