We demonstrate that resonant 32.3 THz pumping of f-f transitions in the samarium ions in SmFeO 3 leads to a nonlinear regime of radiation-matter interaction. The nonlinearity arises from the photoinduced population of the excited state, the dynamics of which was studied in a pump-probe experiment. The measurements have been performed in the spectral range near the
Experimental study of spatial and temporal evolution of a dielectric barrier discharge (DBD) during a single current pulse is reported. The discharge light emission has been imaged using a high-speed intensified charge-coupled device camera. The time-resolved light emission data have been combined with the discharge current and applied voltage waveforms measurements. The discharge behavior has been found to be dependent on the external circuit impedance and bandwidth. Being nonstationary in principle, the DBD can exhibit both time evolution and development over the electrode area. For a typical DBD setup with flat parallel electrodes, the discharge breakdown occurs in the electrode’s central part; then, the plasma column expands to the electrode’s peripheries and gradually fills up the entire electrode area. The powering system should be able to provide enough current value during the discharge glow to achieve a simultaneous breakdown over the whole electrode area. In this case, the discharge appears over the entire electrode’s area and the plasma column exhibits temporal evolution only. The measured discharge characteristics for different power supply architectures had shown the evidence of a “normal current density” effect in DBD glow.
Complete population inversion is demonstrated analytically in the strong field limit in a three level system using the rubidium 5s-5p-5d transition. We exploit the pre-transients of an amplitude shaped laser pulse to direct the dynamics of the Rabi oscillations such that the population transfer to the excited state can be controlled in a wide range from a strongly enhanced to vanishing one. The excitation is performed under off-resonant conditions. During the intense ultrafast pulse levels shift to such an extent that two-photon resonant excitation becomes possible, even though a frequency spectrum does not contain photons with energies necessary for excitation of an unperturbed system. Within the reach of experimental parameters we demonstrate 70% population transfer.
In this work we present experimental results concerning electrode sheath and ion flux formation near a concave electrode with the dimension of a cavity comparable to the electrode sheath length. It is shown that the secondary electron emission can play a crucial role in plasma molding over the electrode surface. It is also observed that plasma has a tendency to "self-leakage" in electrode cavities.
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