The giant dipole vortex

Abstract

The field lines of energy flow of radiation emitted by an oscillating electric dipole in free space are either straight lines (linear dipole) or they form a vortex (rotating dipole). When the dipole is embedded in a material, the properties of the medium affect the direction of energy flow. Damping due to the imaginary part of the relative permittivity ${\mathit{\epsilon }}_{\text{r}}$ makes the field lines curve for the case of a linear dipole, and for a rotating dipole, the shape of the vortex is altered. In addition, a negative value of the real part of ${\mathit{\epsilon }}_{\text{r}}$ has the effect that the rotation direction of the vortex reverses for the case of a rotating dipole. The value of the relative permeability ${\mathit{\mu }}_{\text{r}}$ has in general not much effect on the redistribution of the direction of energy propagation. We show that a dramatic effect occurs when the embedding material is near-single-negative (both ${\mathit{\epsilon }}_{\text{r}}$ and ${\mathit{\mu }}_{\text{r}}$ approximately real, and the real parts of opposite sign). The curving of field lines is in general a sub-wavelength phenomenon. For near-single-negative materials, however, this curving extends over large distances from the dipole. In particular, the small free-space vortex of a rotating dipole becomes a vortex of enormous dimensions when the radiation is emitted into a near-single-negative material.

Keywords:

• Electric dipole
• Poynting vector
• optical vortex

Disclosure statement

No potential conflict of interest was reported by the authors.