Fig. 7: The x and y components of the transmitted electric field form a Lissajous figure, which originates from the beating between the frequency of the input wave ω = 1 and that of the screw Ω.

The commensurability ratio between the two determines the number of lobes in the figure. For RHP input (a-b) the screw is able to amplify the waves as they propagate through a thickness d. By contrast, a LHP input wave (c-d) is not amplified, but additional beating results from the additional, distinct real eigenvalue.