Photonic angular momentum: progress and perspectives
Andrew Forbes, Siddharth Ramachandran, Qiwen Zhan
Abstract
Although the existence of photonic angular momentum is imbedded in Maxwell's equations, the full picture of its intricate connections was slow to emerge. Early work on polarization and energy flow were connected by Poynting [1] and used to predict the mechanical potential of spin angular momentum (SAM) from circularly polarized light, later confirmed by Beth Although photonic orbital angular momentum was very well known since the early days of quantum mechanics, creating photons with orbital angular momentum (OAM) was restricted to unlikely quadrupole transitions in atoms, and remained the realm of textbook atomic physics until only 30 years ago This seminal work revealed the importance of the spatial structure of light, particularly its helical phase, and its connection to OAM. The explosion of activity that followed was fueled by the ease by which OAM light could be created, bringing photonic angular momentum tools into optical laboratories.