  Huygens sources are elements that scatter light in the forward direction as
used in the Huygens-Fresnel principle. They have remained fictitious until
recently where experimental systems have been fabricated. In this letter, we
propose isotropic meta-atoms that act as Huygens sources. Using clusters of
plasmonic or dielectric colloidal particles, Huygens dipoles that resonate at
visible frequencies can be achieved with scattering cross-sections as high as 5
times the geometric cross-section of the particle surpassing anything
achievable with a hypothetical simple spherical particle. Examples are given
that predict extremely broadband scattering in the forward direction over a
1000 nm wavelength range at optical frequencies. These systems are important to
the fields of nanoantennas, metamaterials and wave physics in general as well
as any application that requires local control over the radiation properties of
a system as in solar cells or bio-sensing.
