Abstract
Attosecond angular streaking measurements have revealed deep insights into the timing of tunnel ionization processes of atoms in intense laser fields. So far experiments of this type have been performed only with a cold-target recoil-ion momentum spectrometer (COLTRIMS). Here, we present a way to apply attosecond angular streaking experiments to a velocity map imaging spectrometer (VMIS) with few-cycle pulses at a repetition rate of 10 kHz and a high ionization yield per pulse. Three-dimensional photoelectron momentum distributions from strong-field ionization of helium with an elliptically polarized, sub-10-fs pulse were retrieved by tomographic reconstruction from the momentum space electron images and used for the analysis in the polarization plane.
Highlights
In recent years, a number of experiments using the attoclock technique [1, 2] have addressed fundamental questions in ultrafast science, including tunneling delay time [2, 3], tunnel geometry [3] release times [4] and correlations [5] in sequential double ionization [4]
A velocity map imaging spectrometer (VMIS) images only two-dimensional projections of the charged particle distribution, typically in the set of planes that are perpendicular to the polarization plane
The demand to exploit the momentum distribution in three dimensions and in particular the polarization plane is fulfilled by the combination of VMI and tomographic reconstruction that has been used by various groups in several applications in atomic, molecular and optical science [10,11,12,13]
Summary
A number of experiments using the attoclock technique [1, 2] have addressed fundamental questions in ultrafast science, including tunneling delay time [2, 3], tunnel geometry [3] release times [4] and correlations [5] in sequential double ionization [4]. This maximum electric field is along the main axis of the polarization ellipse Both the clock and the start of the tunneling process (i.e. time zero) is experimentally fully accessible with a simple independent laser polarization measurement and a standard pulse characterization using for example the SPIDER technique [15]. The tunneling delay time is reconstructed from the angular coordinate of the final electron momentum vector, typically measured with the COLTRIMS apparatus This measurement is based on the “peak search in electron counts” as a function of the angle offset of time zero and does not need to resolve the tunneling probability distribution which is still present. The key elements of an attoclock measurement are elliptically polarized fewcycle pulses, accurate polarization control and a detector that is capable of imaging three dimensional momentum distributions of charged particles (electrons or ions)
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