Atomic spectroscopy with twisted photons: Separation of M1−E2 mixed multipoles

Abstract

We analyze atomic photoexcitation into the discrete states by twisted photons, or photons carrying extra orbital angular momentum along their direction of propagation. From the angular momentum and parity considerations, we are able to relate twisted-photon photoexcitation amplitudes to their plane-wave analogues, independently of the details of the atomic wave functions. We analyzed the photo-absorption cross sections of mixed-multipolarity E2 − M1 transitions in ionized atoms and found fundamental differences coming from the photon topology. Our theoretical analysis demonstrates that it is possible to extract the relative transition rates of different multipolar contributions by measuring the photo-excitation rate as a function of the atom's position (or the impact parameter) with respect to the optical vortex center. The proposed technique for separation of multipoles can be implemented if the target's atom position is resolved with sub-wavelength accuracy, for example, with Paul traps. Numerical examples are presented for Boron-like highly-charged ions (HCI).

Excitation of E1-forbidden atomic transitions with electric, magnetic, or mixed multipolarity in light fields carrying orbital and spin angular momentum [Invited]

“…For the system with M1 transitions, or partial wave amplitude with j = 1, choose θ z = π/2; for E2 or j = 2, choose θ z = π/4; and for E3 or j = 3, choose again θ z = π/2. For the Boron-like 20 Ne 5+ HCI, the M1 and E2 partial waves are unusually similar, leading to effects shown in this paper; see also [32]. This makes this HCI a promising candidate for future experimental research of topological effects in light-matter interactions.…”

“…In this paper we focus our attention on OAM-photons interacting with single trapped ions. The possibility to enhance and control weak atomic transitions was discussed in [32], where the authors foreseen OAM-modes being used is high precision atomic spectroscopy. Particular interest in the field has been payed to light-matter interactions in the case of beams carrying a well-defined OAM [33][34][35][36].…”

Spin polarization of photoelectrons in GaAs excited by twisted photons

“…where R identifies the position of a particular bound electron with respect to the photon beam quantization axis. This is the result identical to the one for photoexcitations of single trapped ions, developed in [25,36]. It is important to note the convenient separation of the terms responsible for OAM-transfer in the underbracket eqn.…”

Polarization transfer from the twisted light to an atom

“…In special circumstances, interesting results occur when there are two different amplitudes of comparable magnitude. Such results have been discussed in [10,11], albeit without the emphasis on separating the longitudinal and traverse contributions that we are providing here.…”