LAUSR

We study photoelectron angular distributions (PADs) near the ionization threshold with a newly developed Coulomb quantum-orbit strong-field approximation (CQSFA) theory. The CQSFA simulations exhibit an excellent agreement with the result from the time-dependent Schr\"odinger equation. We show that the low-energy fan-shaped pattern in the PADs corresponds to a subcycle time-resolved holographic structure and stems from the significant influence of the Coulomb potential on the phase of the forward-scattered electron trajectories, which affects different momenta and scattering angles unequally. Our work provides a direct explanation of how the fan-shaped structure is formed, based on the quantum interference of direct and forward-scattered orbits. Moreover, our work shows that the fan-shaped pattern can be used to extract information on the target structure, as the number of fringes in the PADs depends strongly on the symmetry of the electronic bound state.