Using focus ion beam (FIB), we milled in an opaque gold film a clockwise (right R ) or anticlockwise (left L ) Archimedian spiral grooves around a central subwavelength hole. The polar equation ( ρ, θ ) of the left handed Archimedian spiral is ρ = P · θ/ (2 π ), and the right handed enantiomeric spiral is obtained by reflection across the y axis (see Fig. 1). The geometrical parameter P is the radial grating period and we take its value equal to the FIG. 1: Chiral plasmonic metamolecules. On the top panel: scanning electron micrographs of the left (L) and right (R) handed enantiomer (mirror image) planar chiral structures investigated. The scale bare is 3 µ m long. The parameters characterizing the structure are the following: hole diameter d = 350 nm, film thickness h = 310 nm, grating period P = 760 nm, groove width w = 370 nm, and groove depth s = 80 nm. The structures are milled, with a focus ion beam, in a gold film deposited on a glass substrate. On the bottom panel: transmission spectra at normal incidence of individual left (blue curve) and right handed (red curve) Archimede spirals illuminated from the air side. 4