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March 2nd, 2012, 03:14 PM   #1
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orbital angular momentum (OAM) of EM wave, is it possible.

I came across this news today. This is not a physics forum but the equations used in this paper makes no sense at all. The EM wave equations. I am sorry, I am yet to learn to post equations with symbols in this forum.

Could not any of our members enligten me on this issue.

Quote:
One way is to exploit fundamental physical properties of the EM field that hitherto have not been utilized in radio communications. To this end, we recall that the EM field can carry both energy and momentum. Whereas the Poynting vector S and the concomitant linear momentum (rational units) are associated with force action and therefore with translational dynamics, the angular momentum is a conserved physical observable (constant of motion) that is associated with torque action and thus with rotational dynamics. In a beam geometry as used in radio communications, the total angular momentum can be conveniently expressed as the sum of two components: J = ? + L. The component ? represents the spin angular momentum (SAM), related to the polarization of the individual EM waves of the beam and thus with photon helicity. The component L represents the lesser-known orbital angular momentum (OAM) associated with the helicoidal phase profile of the EM beam in the direction orthogonal to the propagation axis. In a quantum picture L can be described as a superposition of discrete photon quantum eigenstates, each with a well-defined OAM value ?,? = 0,1,2,... [47]. Hence, not only in mechanics but also in electromagnetism, OAM is a fundamental physical quantity that spans an infinite state space
Source : http://iopscience.iop.org/1367-2630/14/3/033001/article
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