For recollision in simple systems, trajectory dynamics are well understood and the emitted attosecond pulse phase is predominantly shaped by electron continuum dynamics. In more complex systems, however, the phase of the emitted pulse can be significantly affected by recombination effects [1, 2, 3]. Measuring trajectory dynamics is done either by measuring the emitted attosecond pulse directly (i.e. ex situ) , or by perturbing the recollision process with a weak field (i.e. in situ) . Previous works, through the study of two-centre interference, have shown that in situ measurements are insensitive to the recombination phase and are sensitive only to the continuum propagation of the recolliding electron .
I will show that in situ techniques can be sensitive to the recombination phase by discussing two kinds of systems. First, I will discuss an experimental non-collinear in situ measurement of the group delay around the Cooper minimum in argon and compare these results with ab initio simulations of a collinear w-2w in situ measurement in argon. I will then discuss the study of multielectron dynamics and excitations during recollision using in situ methods by discussing experimental measurements of recollision-induced plasmon excitation in xenon and accompanying simulations .
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