| Abstract: | Several of our groups deal for long time with photons “carrying” angular momentum. But the mechanical characteristics of photons (momentum, angular momentum…) are highly controversial. We show that there are different photonic linear momenta and infinite number of photonic angular momentum types, starting from helicity, followed by spin, then infra-zilches etc. A photon may carry also an unquantized spin (transverse). These are all the direct result of the massless spin 1 character of the photon. In addition, as any quantum wave, a photon can potentially carry also orbital angular momentum which complements its total angular momentum. We present some controversies, e.g. while photonic spin is related to circular polarization – a circularly polarized plane wave does not carry angular momentum; can photon spin and orbital angular momentum can be separated and is this separation unique? In matter things are becoming even more complicated and even the linear momentum of photons is still controversial (Abrahams vs Minkovsky). Finally, light matter interactions, manifested as delivering of the angular momentum from the photon to matter will be discussed and it will be shown that the interacting matter is mainly “measuring itself” and not “receiving” the angular momentum from the interacting photon – which is exemplified by electronic transitions with change of angular momentum while the absorbed photon does not carry angular momentum at all. Related chirality of light (and local chirality) will be mentioned. |