Orbital angular momentum of twisted light: chirality and optical activity

Abstract Optical activity is conventionally understood as a natural difference in the optical responses of chiral materials with opposite handedness. It stems from quantised spin angular momentum ± ħ per photon, representing either left- or right-handed circular polarisations. Less well known, until recently, was possibility that matter might also respond similar, discriminatory way to handedness twisted light, ‘optical vortices’, whose orbital (OAM) ℓ ℏ where topological charge sign determines wavefront twist left right. Initial studies focusing on whether, spectroscopic applications, differently vortex $ + \ell + and - − beams, failed identify any viable mechanism. However, last few years, theory experiment have both supplied ample evidence that, under certain conditions, such forms interaction do exist—and result, field chirality OAM beginning flourish at pace. This topical review presents survey this new field, working up description those initial cutting-edge experiments now taking place. Analysing fundamental mechanisms provides for revision previous precepts, broadening their scope light recent advances understanding, highlighting vibrant synergy between fields light.