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Type: Article × Subject: Coherence properties ×

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    Space-time focusing and coherence properties of supercontinua in multipass cells
    (College Park, MD : APS, 2021) Mei, Chao; Steinmeyer, Günter
    The situation of self-compression and concomitant supercontinuum generation in a multipass cell is analyzed in numerical simulations. This study focuses on multipass cells that contain a dielectric slab as nonlinear medium and overcompensate the dispersion of the slab with intracavity dispersive coatings. A 2D+1 unidirectional pulse propagation equation is utilized to simulate the pulse evolution through successive passes. We observe a previously unreported effect of space-time focusing, leading to a pronounced blue shift, similar to what had been observed in filament compression experiments before. This effect competes with detrimental pulse breakup, which can nevertheless be mitigated under suitable choice of cavity parameters. We further analyze resulting coherence properties, in both the time and frequency domains. Our analysis shows highly favorable properties of multipass cell compression schemes when nonlinearity and dispersion are distributed over as many cavity passes as possible. This quasicontinuous approach is particularly promising for spectral broadening schemes that allow for stabilization of the carrier-envelope phase.
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    Vectorial nonlinear coherent response of a strongly confined exciton-biexciton system
    (Bristol : IOP, 2013) Kasprzak, J.; Portolan, S.; Rastelli, A.; Wang, L.; Plumhof, J.D.; Schmidt, O.G.; Langbein, W.
    The vectorial four-wave mixing response of an individual strongly confined exciton-biexciton system with fine-structure splitting in a GaAs/AlGaAs quantum dot is measured by dual-polarization heterodyne spectral interferometry. The results are compared with theoretical predictions based on the optical Bloch equations. The system is described by a four-level scheme, which is a model system of the nonlinear excitonic response in low-dimensional semiconductors. We measure its coherence properties and determine the underlying dephasing mechanisms. An impact of the inhomogeneous broadening by spectral wandering on the coherent response is investigated. We further discuss the different four-wave mixing pathways, polarization selection rules, the time-resolved polarization state, the vectorial response in two-dimensional four-wave mixing and ensemble properties.