Measuring an offset angle of the peak photoelectron momentum distribution in the polarization plane of a close-to-circularly polarized laser field applied to an atomic target has been used to determine the tunnelling time which the photoelectron spends under the subsequently formed barrier.

Once the photoelectron leaves the tunnel at the peak value of the electric field, the most probable detection direction will be aligned with the vector potential at the instant of tunnelling. This direction is tilted by 90 degrees relative to the electric field at this instant. A measurable angular offset from this axis has been typically associated with the time the photoelectron spends under the barrier. Such a measurement is termed colloquially the attoclock.

In this talk we will present the details of our work aiming to instead explain these measurements through a combination of classical scattering and Keldysh tunnelling theory.