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Register a new userFormulation of the twisted-light--matter interaction at the phase singularity: beams with strong magnetic fields
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Added by
Guillermo Federico Quinteiro
Publication date
2016
fields
Physics
and research's language is
English
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The formulation of the interaction of matter with singular light fields needs special care. In a recent article [Phys.~Rev.~A {bf 91}, 033808 (2015)] we have shown that the Hamiltonian describing the interaction of a twisted light beam having parallel orbital and spin angular momenta with a small object located close to the phase singularity can be expressed only in terms of the electric field of the beam. Here, we complement our studies by providing an interaction Hamiltonian for beams having antiparallel orbital and spin angular momenta. Such beams may exhibit unusually strong magnetic effects. We further extend our formulation to radially and azimuthally polarized beams. The advantages of our formulation are that for all beams the Hamiltonian is written solely in terms of the electric and magnetic fields of the beam and as such it is manifestly gauge-invariant. Furthermore it is intuitive by resembling the well-known expressions in the dipole-electric and dipole-magnetic moment approximations.
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Twisted light is light carrying orbital angular momentum. The profile of such a beam is a ring-like structure with a node at the beam axis, where a phase singularity exits. Due to the strong spatial inhomogeneity the mathematical description of twisted-light--matter interaction is non-trivial, in particular close to the phase singularity, where the commonly used dipole-moment approximation cannot be applied. In this paper we show that, if the polarization and the orbital angular momentum of the twisted-light beam have the same sign, a Hamiltonian similar to the dipole-moment approximation can be derived. However, if the signs of polarization and orbital angular momentum differ, in general the magnetic parts of the light beam become of significant importance and an interaction Hamiltonian which only accounts for electric fields, as in the dipole-moment approximation, is inappropriate. We discuss the consequences of these findings for twisted-light excitation of a semiconductor nanostructures, e.g., a quantum dot, placed at the phase singularity.
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