Observation of coherent transients in ultrashort chirped excitation of an undamped two-level system.

The effects of coherent excitation of a two-level system with a linearly chirped pulse are studied theoretically and experimentally [in Rb (5s-5p)] in the low field regime. The coherent transients are measured directly on the excited state population on an ultrashort time scale. A sharp step corresponds to the passage through resonance. It is followed by oscillations resulting from interferences between off-resonant and resonant contributions. We finally show the equivalence between this experiment and Fresnel diffraction by a sharp edge.

Single-shot real-time characterization of chirped-pulse amplification systems by spectral phase interferometry for direct electric-field reconstruction.

We characterize chirped-pulse amplification systems by using spectral phase interferometry for direct electric-field reconstruction. For the first time to the authors' knowledge, single-shot real-time operation has been obtained for this technique, leading to a fast and accurate optimization of these systems.