Twisty light tells left-handed molecules from right

A super twisty beam of light has been created that can distinguish between left and right-handed molecules with unprecedented precision.

Molecules often come in mirror images that can have different properties, and researchers take advantage of this "chirality" to design new drugs. They sort left from right versions using circularly polarised light, whose electric field corkscrews through space in a left or right-handed direction. Unfortunately, the technique often fails when the light's coils are bigger than the molecules themselves.

Now Yiqiao Tang and Adam Cohen of Harvard University have created "superchiral" light that twists very tightly in places. To make it, they shone a right-handed green laser beam at a mirror and let it interact with the left-handed reflection.