Fig. 4. Spectrally filtered plasmon cathodoluminescence maps.

a–l Band-pass filtered (BP) CL images of spiral channels with arm separations equal to λ_SPP, 2 λ_SPP, and 3 λ_SPP. The BP filters are centered at 445 nm a–c, 513 nm d–f, 586 g–i, and 685 nm j–l, and exhibit the vortex response of the OAM mode, generated by the phase of the plasmon modes. m–o Unfiltered CL images of the same spiral channels, showing that the phase-induced effects are only detected with spectral selectivity, and cannot be seen in the spectrally integrated luminescence of the system. Scale bars = 1 μm