Vacuum-ultraviolet to infrared supercontinuum in hydrogen-filled photonic crystal fiber

Although supercontinuum sources are readily available for the visible and near infrared (IR), and recently also for the mid-IR, many areas of biology, chemistry, and physics would benefit greatly from the availability of compact, stable, and spectrally bright deep-ultraviolet and vacuum-ultraviolet (VUV) supercontinuum sources. Such sources have, however, not yet been developed. Here we report the generation of a bright supercontinuum, spanning more than three octaves from 124 nm to beyond 1200 nm, in hydrogenfilled kagomé-style hollow-core photonic crystal fiber (kagomé-PCF). Few-microjoule, 30 fs pump pulses at wavelength of 805 nm are launched into the fiber, where they undergo self-compression via the Ramanenhanced Kerr effect. Modeling indicates that before reaching a minimum subcycle pulse duration of ∼1 fs, much less than one period of molecular vibration (8 fs), nonlinear reshaping of the pulse envelope, accentuated by self-steepening and shock formation, creates an ultrashort feature that causes impulsive excitation of long-lived coherent molecular vibrations. These phase modulate a strong VUV dispersive wave (at 182 nm or 6.8 eV) on the trailing edge of the pulse, further broadening the spectrum into the VUV. The results also show for the first time that kagomé-PCF guides well in the VUV.