Nondipole Time Delay in the Photoionization of Atomic Systems

It has recently been shown that, owing to their opposite parities, dipole and quadrupole contributions to attosecond photoionization time delays behave differently as a function of detection angle; specifically, one is symmetric under a transformation from θ to 180- θ while the other in antisymmetric, so that by adding or subtracting the time delay at the complementary angles, the dipole contribution cancels out and the quadrupole contribution can be observed [1]. In the light of this understanding, it is useful to study the quadrupole time delays. A theoretical investigation has been initiated using the relativistic-random-phase approximation (RRPA) [2] to investigate quadrupole time delays in a variety of atomic systems. As a first step, the situation for Ne has been explored for all subshells over a broad range of energies from threshold to several keV. The quadrupole time delays in Ne show tendencies similar to dipole results [3]. The calculations will be extended to other atomic systems including the other noble gas atoms, various atomic ions, and confined atoms. [1] M. Amusia and L. Chernysheva, JETP Lett. 112, 673 (2020). [2] W. R. Johnson and C. D. Lin, Phys. Rev. A 20, 964 (1979). [3] A. S. Kheifets, et al Phys. Rev. A 92, 063422 (2015).