Spatio-temporal effects in resonant multiphoton ionisation of the caesium atom

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Abstract
The time evolution of a resonance peak is studied for three- and four-photon ionisation of the caesium atom with square and Gaussian laser pulses. In the domain 10-13-10-7s two different regimes are defined according to whether the time is smaller or larger than a characteristic time tc. For ttc. The corresponding resonance width varies as t-1 in the first case becomes intensity independent in the second. The effects of the spatial distribution of the intensity in the focal volume are discussed and an excellent agreement is found between the theoretical and experimental values of the order of non-linearity, the resonance width and the absolute magnitude of the ion signal.