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.

2016-12-25, Rupp, Philipp, Seiffert, Lennart, Liu, Qingcao, Süßmann, Frederik, Ahn, Byungnam, Förg, Benjamin, Schäfer, Christian G., Gallei, Markus, Mondes, Valerie, Kessel, Alexander, Trushin, Sergei, Graf, Christina, Rühl, Eckart, Lee, Jinwoo, Kim, Min Su, Kim, Dong Eon, Fennel, Thomas, Kling, Matthias F., Zherebtsov, Sergey

The excitation of nanoscale near-fields with ultrashort and intense laser pulses of well-defined waveform enables strongly spatially and temporally localized electron emission, opening up the possibility for the generation of attosecond electron pulses. Here, we investigate the electron photoemission from isolated nanoparticles of different materials in few-cycle laser fields at intensities where the Coulomb field of the ionized electrons and residual ions significantly contribute to the electron acceleration process. The dependences of the electron cut-off energy on the material’s dielectric properties and electron binding energy are investigated systematically in both experiments and semi-classical simulations. We find that for sufficiently high near-field intensities the material dependence of the acceleration in the enhanced near-fields is quenched by many-particle charge-interaction.