Investigation of a Virtual Torsive Space from Twisted Optical Slits

Two twisted slits do not show the path of light expected from simple ray optics, so we performed a calculation based on Huygens' elementary waves to obtain the "true path" (Frins et al. DGaO-Proc. 2018). The region of the stationary phase, which we call the Huygens-surface HF, has the form of a 180°-twisted band which goes through the slits and is "virtual" in its part between and in front of the lenses in the sense of the virtual focus of a concave lens. In this work we analyse the complex theoretical structure of the Huygens-surface and assign its characteristic features to optical phenomena like foci, caustics, and light stops with conjugate points of the Van Vleck formula and aperture points. A wider second slit favours collective particle effects like the Gouy phase, while a narrow slit suppresses them and accentuates the torsion of space. We also discuss the possibility of further measurements to find optical access to the virtual region of this space.