A RABBITT attoclock for the direct measurement of photoionization time delays

We propose the ``RABBITT attoclock'', an XUV-pump IR-probe photoionization scheme that employs isolated pairs of counter-rotating consecutive harmonics, such as those produced with bi-circular fields [1-2], in conjunction with angularly resolved detectors. This method differs from Rainbow RABBITT [3] in two major respects: i) it gives direct access to rapidly varying photoemission delays, thus eliminating the interference from the continuum-continuum probe stage, and ii) it does not require any time-delay scan. The scheme is based on the interference between one-photon and two-photon ionization pathways whose phase difference is imprinted in the photoelectron anisotropy. We illustrate the method with \emph{ab initio} simulations [4,5] of the resonant ionization of the helium atom, showing that the angular photoelectron distribution exactly reproduces the rapid excursion of the scattering phase shift near the $(2s2p)^1$P$^{\rm o}$ resonance. [1] O. Kfir~{\it et al.}, Nat. Photonics {\bf 9}, 99 (2015). [2] P.-C. Huang~{\it et al.}, Nat. Photonics {\bf 12}, 349 (2018). [3] V. Gruson~{\it et al.}, Science {\bf 354}, 734 (2016). [4] L. Argenti~{\it et al.} Phys. Rev. A {\bf 87}, 053405 (2013). [5] S. Donsa~{\it et al.} arXiv:1811.09110 [physics.atom-ph].