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How to twist light into a Möbius strip

The team used a green laser beam that was a superposition of two waves with opposing spin. The result was a beam with a polarization that varied across its width. It was circularly polarized at its centre, but linearly polarized – and with varying orientations of the polarization vector – further out. To extend this 2D pattern of polarizations into the third dimension, the researchers sent the beam through a tight-focusing microscope lens. This gave the beam a longitudinal component – the size of which depended on the degree of focusing. The result was a Möbius strip of polarization that measured just 200–250 nm across. (link)