Erlangen 2018 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 64: Quantum Optics and Photonics IV

Q 64.5: Talk

Friday, March 9, 2018, 11:30–11:45, K 0.016

Coherent Raman gain suppression in gas-filled broadband-guiding photonic crystal fibres — •Manoj K. Mridha, Pooria Hosseini, David Novoa, and Philip St.J. Russell — Max Planck Institute for the Science of Light, Erlangen, Germany

The gain for stimulated Raman scattering (SRS) gets strongly suppressed when the rate of phonon creation (via pump-to-Stokes conversion) is equally compensated by the rate of phonon annihilation (via pump-to-anti-Stokes conversion). This occurs when the Raman coherence waves--synchronous oscillations of a large population of molecules--have identical propagation constants for both processes; i.e., they are phase-velocity matched. This phenomenon, first predicted more than half a century ago, has recently been demonstrated in the collinear geometry provided by a hydrogen-filled photonic crystal fibre pumped in the vicinity of its zero-dispersion wavelength. Here we report that Raman gain suppression is a universal feature of SRS in gas-filled hollow-core fibres and that it can strongly weaken SRS even under conditions of large phase mismatch, especially at high pump powers when it is normally assumed that nonlinear processes become more (not less) efficient. This counterintuitive behavior at high pump power implies the domination of Stokes growth in a different core mode compared to the pump (for example LP01/pump to LP11/ Stokes). These results have important implications for fibre-based Raman amplifiers, shifters, or frequency combs, especially for operation in the ultraviolet, where the Raman gain is very high.