# Circular holographic ionization-phase meter

## TL;DR

The paper introduces a novel attosecond measurement technique called CHIP that directly measures ionization phases and photoemission amplitudes using circularly polarized harmonics and angular photoelectron detection.

## Contribution

It presents the CHIP method, enabling direct phase measurement of ionization processes and photoemission amplitudes from a single measurement, demonstrated through ab initio helium simulations.

## Key findings

- Successfully captures rapid phase changes in autoionizing resonances.
- Provides access to phase information of even-parity continuum states.
- Demonstrates the method's effectiveness with helium autoionization simulations.

## Abstract

We propose an attosecond XUV-pump IR-probe photoionization protocol that employs pairs of counter-rotating consecutive harmonics and angularly resolved photoelectron detection, thereby providing direct measurement of ionization phases. The present method, which we call circular holographic ionization-phase meter (CHIP), gives also access to the phase of photoemission amplitudes of even-parity continuum states from a single time-delay measurement, since the relative phase of one- and two-photon ionization pathways is imprinted in the photoemission anisotropy. The method is illustrated with \emph{ab initio} simulations of photoionization via autoionizing resonances in helium. The rapid phase excursion in the transition amplitude to both the dipole-allowed $(2s2p)^1$P$^{\rm o}$ and the dipole-forbidden $(2p^2)^1$D$^{\rm e}$ states are faithfully reproduced.