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Attosecond pulses are generated in the interaction between a macroscopic number of ionizing atoms and an intense, focused laser beam. This talk will give an overview of how collective effects such as phase matching and ionization-induced reshaping are crucial for the generation and preservation of attosecond structures in the non-linear medium.
It is these collective effects that often allow us to distill single atom characteristics from the generation process. A well-known example is the phase matching-induced spatial separation of the long and short quantum trajectories that contribute to high harmonic generation. The spatial separation simplifies the phase locking of consecutive harmonics and facilitates the generation of well behaved attosecond pulse trains. In an example of collective effects in the generation of single attosecond pulses, we have recently shown that ionizaton induced spatiotemporal reshaping of the driving laser pulse makes it possible to isolate individual attosecond pulses from driving pulses as long as 10 femtoseconds. Finally, we emphasize that any attosecond control scheme based on single atom characteristics of the harmonic generation process will only be effective if the control parameter can be kept constant throughout the interaction volume. |
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