Landau condensation of the M=+or-3, odd-parity, quasi-hydrogenic caesium spectra is investigated for fields up to 8 T and for energies ranging +or-120 cm -1 around the threshold. Continuous single-mode dye laser excitation is used. A dominant series of sharp discrete lines is shown to follow the semiclassical predictions from the Landau to the diamagnetic Coulomb regimes where the lines branch to well defined states of the hydrogenic manifolds. For this highly hydrogenic spectrum, the spacing of the resonances near the threshold is shown to be 1.5 h(cross) omega c .
An excitonic approach to the ultrafast optical response of confined semiconductors at elevated densities below the Mott transition is presented. The theory is valid from the coherent regime, where coherent excitonic transitions and biexcitons dominate, to the incoherent regime, where excitonic occupations dominate. Numerical simulations of the
1s exciton dynamics during intense circularly polarized pump pulses in two different Coulomb-interaction regimes are performed for two-dimensional semiconductors: Moderate Coulomb interaction is compared with dominating Coulomb interaction with respect to the light-matter interaction strength. The different many-body contributions are disentangled and it is found, that excitonic Rabi oscillations in the Coulomb-dominated regime are considerably less strong. By also comparing circular and linear excitation in a MoSe
2 monolayer, it is found, that linear excitation creates a regime, where excitonic Rabi oscillations are almost completely suppressed.