Teǧin, U.Ortaç, B.2018-04-122018-04-1220171041-1135http://hdl.handle.net/11693/37117We study the spatiotemporal instability generated by a universal unstable attractor in normal dispersion graded-index multimode fiber for femtosecond pulses for the first time. Experimentally observed spatiotemporal instability sidebands are 91-THz detuned from the pump wavelength of 800 nm. Detailed analysis carried out numerically by employing coupled-mode pulse propagation model. Numerically obtained results are well-aligned with experimental observations. Spatial evolution of the total field and spatiotemporal instability sidebands is calculated numerically, and for the input pulses of 200-fs duration, formation and evolution of spatiotemporal instability are shown in both spatial and temporal domains. Our results present the unique features of spatiotemporal instability, such as remarkable frequency shift with inherited beam shape of instability sidebands.EnglishGraded-index multimode fibersNonlinear fiber opticsSpatiotemporal pulse propagationUltra-short pulsesElectromagnetic pulseFibersStabilityUltrafast lasersUltrashort pulsesFormation and evolutionsGraded-Index Multimode fibersNonlinear Fiber-OpticsNormal dispersionPulse propagation modelSpatial evolutionSpatio-temporal instabilitySpatiotemporal pulseMultimode fibersArticle10.1109/LPT.2017.2769343