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M. I. Stockman
dark (“off”) arena, fully separates plasmonic effects from photonic effects and in
addition is the necessary starting point for later focusing and scanning experiments.
Any intensity detected inside the arena is purely plasmonic.
Adapting from Ref. [212], we present the achieved SPP focusing in Fig. 1.24.
A phase optimization loop is used to focus SPPs at a pre-chosen target. This loop
yields the optimal phase for each launching pad (“superpixel”) as well as the relative
intensity to focus. The amplitude profile is the same in all cases including the bare
gold case, with four launching areas and a central dark arena where only SPPs can
propagate. The incident polarization is diagonal in relation to the grating lines so as
to have all available angles (2π range) contributing to the focus, thereby maximizing
the numerical aperture and resolution.
Successful focusing at the center of the SPP arena is shown in Fig. 1.24a. The
structured SPP wavefront produces an intensity in the designated target that is at least
20 times higher than the average SPP background of an unstructured wavefront. The
measured size of the plasmonic focus is 420 nm, consistent with the diffraction limit
of the SPPs. The flexibility of the method (scanning the focus) is demonstrated in
Figs. 1.24b, c, which shows the SPP focus relocated without mechanical motion to
controlled positions in the plasmonic arena.
Fig. 1.24 Experiment on coherent control (dynamic focusing) of SPPs. Adapted from Ref. [212].
a Relative phases of the superpixels are optimized to focus SPPs at the center of the SPP arena. The
intensity in the target spot is purely plasmonic and 20 times higher than the average background of
an unstructured plasmonic wavefront. The focus size is diffraction limited by the detecting optics.
b, c, Demonstration of SPP focusing on freely chosen targets in the SPP arena. d Background
reference of an unstructured SPP wavefront (uniform phase profile)
M. I. Stockman
dark (“off”) arena, fully separates plasmonic effects from photonic effects and in
addition is the necessary starting point for later focusing and scanning experiments.
Any intensity detected inside the arena is purely plasmonic.
Adapting from Ref. [212], we present the achieved SPP focusing in Fig. 1.24.
A phase optimization loop is used to focus SPPs at a pre-chosen target. This loop
yields the optimal phase for each launching pad (“superpixel”) as well as the relative
intensity to focus. The amplitude profile is the same in all cases including the bare
gold case, with four launching areas and a central dark arena where only SPPs can
propagate. The incident polarization is diagonal in relation to the grating lines so as
to have all available angles (2π range) contributing to the focus, thereby maximizing
the numerical aperture and resolution.
Successful focusing at the center of the SPP arena is shown in Fig. 1.24a. The
structured SPP wavefront produces an intensity in the designated target that is at least
20 times higher than the average SPP background of an unstructured wavefront. The
measured size of the plasmonic focus is 420 nm, consistent with the diffraction limit
of the SPPs. The flexibility of the method (scanning the focus) is demonstrated in
Figs. 1.24b, c, which shows the SPP focus relocated without mechanical motion to
controlled positions in the plasmonic arena.
Fig. 1.24 Experiment on coherent control (dynamic focusing) of SPPs. Adapted from Ref. [212].
a Relative phases of the superpixels are optimized to focus SPPs at the center of the SPP arena. The
intensity in the target spot is purely plasmonic and 20 times higher than the average background of
an unstructured plasmonic wavefront. The focus size is diffraction limited by the detecting optics.
b, c, Demonstration of SPP focusing on freely chosen targets in the SPP arena. d Background
reference of an unstructured SPP wavefront (uniform phase profile)