CC BY 4.0 UnportedBenoît, AurélienHusakou, AntonBeaudou, BenoîtDebord, BenoîtGérôme, FrédéricBenabid, Fetah2022-04-062022-04-062020https://oa.tib.eu/renate/handle/123456789/8598https://doi.org/10.34657/7636We report on experimental and theoretical demonstrations of an optical comb spectrum based on a combination of cascaded stimulated Raman scattering and four-wave mixing mediated by Raman-induced nonresonant Kerr-type nonlinearity. This combination enabled us to transform a conventional quasiperiodic Raman comb into a comb with a single and smaller frequency spacing. This phenomenon is achieved using a hollow-core photonic crystal fiber filled with 40 bars of deuterium and pumped with a high-power picosecond laser. The resultant comb shows more than 100 spectral lines spanning over 220 THz from 800 nm to 1710 nm, with a total output power of 7.1 W. In contrast to a pure Raman comb, a 120 THz wide portion of the spectrum exhibits denser and equally spaced spectral lines with a frequency spacing of around 1.75 THz, which is much smaller than the lowest frequency of the three excited deuterium Raman resonances. A numerical solution of the generalized nonlinear Schrödinger equation in the slowly varying envelope approximation provides very good agreement with the experimental data. The additional sidebands are explained by cascaded four-wave mixing between preexisting spectral lines, mediated by the large Raman-induced optical nonlinearity. The use of such a technique for coherent comb generation is discussed. The results show a route to the generation of optical frequency combs that combine large bandwidth and high power controllable frequency spacing.enghttps://creativecommons.org/licenses/by/4.0/530DeuteriumNonlinear equationsOptical signal processingPhotonic crystal fibersPicosecond lasersPumping (laser)SpectroscopyWater vaporCascaded four-wave mixingHollow core photonic crystal fiberKerr type nonlinearityNumerical solutionOptical frequency combsOptical nonlinearityParametric wave mixingSlowly varying envelope approximationFour wave mixingArticle