Orbital Angular Momentum (OAM) of light beams and ….pdfVIP

Orbital Angular Momentum (OAM) of light beams and photons C. Barbieri Dept. of Physics and Astronomy University of Padova - Italy 26/08/2012 ICRA Pescara 1 The Orbital Angular Momentum Among the properties of light still poorly exploited in Astronomy, is the Orbital Angular Momentum (OAM) and associated Optical Vorticity (OV), which is instead already used in Chemistry, Biology, and Quantum and classical Communications. M. Harwit (2003, The Astrophys . J.) was the first to point out the interest of OAM for Astronomy, but his paper was largely ignored. We took up and developed some of his ideas, and shall show in the following that OAM can actually be used in Astronomy, e.g. in the optical domain to overcome to Rayleigh criterium of angular resolution, for coronagraphic applications and hopefully to detect intrinsic OAM in celestial sources. In the radio domain, it can be used for interstellar and interplanetary plasma physics diagnostic, for radio interferometry from the Moon, for measuring the rotation of Black Holes. 26/08/2012 ICRA Pescara 2 Total EM field Angular Momentum Electromagnetic (EM) beams do not only carry energy, power (Poynting flux, linear momentum), and spin angular momentum (SAM, wave polarization), but also orbital angular momentum (OAM). The total angular momentum JEM can be separated into two parts [van Enk Nienhuis, 1992]: EM 0 3 * ˆ 3 J E *E d x  E x - x  E e d x   i  0   i i  2i     • the first part is the spin angular momentum (SAM) SEM , a.k.a. wave polar