Fig. 3: Geometry.
From: Conversion of twisted light to twisted excitons using carbon nanotubes

Spiral of arm 1 (red color) with angle θ between sites 1 and 2. The phase of the twisted light is zero along the z-direction (black line).
From: Conversion of twisted light to twisted excitons using carbon nanotubes
Spiral of arm 1 (red color) with angle θ between sites 1 and 2. The phase of the twisted light is zero along the z-direction (black line).