Nondipole transitions in atom excitation by ultrashort laser pulses
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Interaction of a hydrogen atom with an ultrashort laser pulse is considered for the case where the pulse size in the propagation direction is of the same order or less than the characteristic size of the initially occupied state. This situation can be realized for Rydberg atoms interacting with attosecond laser pulses. The perturbation approach is used to estimate the transition amplitudes in the regime of weak excitation. For sufficiently short pulses, this regime can take place even for strong fields. It is shown that ultrashort laser pulses are able to excite nondipole transitions. The time behaviour of the transition amplitudes is studied numerically. It is found to be qualitatively different depending on whether we employ the exact vector potential or its often-used approximation based on the linear Taylor expansion over the coordinate of the propagation direction. However, to the first order of 1/c (c ≈ 137 is the speed of light in au) the amplitudes are very close for the two cases after the interaction is complete.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||Centre for Atomic, Molecular and Surface Physics|
|Publisher:||Institute of Physics|
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