Generation of a VUV-to-visible Raman frequency comb in hydrogen-filled   kagom\'e photonic crystal fiber
  We report the generation of a purely vibrational Raman comb, extending from the vacuum ultraviolet (184 nm) to the visible (478 nm), in hydrogen-filled kagom\'e-style photonic crystal fiber pumped at 266 nm. Stimulated Raman scattering and molecular modulation processes are enhanced by higher Raman gain in the ultraviolet. Owing to the pressure-tunable normal dispersion landscape of the fiber-gas system in the ultraviolet, higher-order anti-Stokes bands are generated preferentially in higher-order fiber modes. The results pave the way towards tunable fiber-based sources of deep- and vacuum ultraviolet light for applications in, e.g., spectroscopy and biomedicine. 
M. K. Mridha, D. Novoa, S. T. Bauerschmidt, A. Abdolvand and P. St.J.   Russell
physics.optics