OAM of Light: Origins and Applications

OAM of Light: Origins and Applications: Comparison

Please note this is a comparison between Version 1 by Olivier Emile and Version 2 by Jessie Wu.

Orbital Angular Momentum (OAM) of light is generating growing interest within the scientific community. This entry reviews the origins and applications of OAM. It is the counterpart of linear momentum for systems in rotation. The general expression of OAM is discussed, followed by its implications in terms of phase distribution and donut-shaped intensity profiles. Applications described include the generation of optical torque, telecommunications enhancement, and the rotational Doppler effect, emphasizing the role and consequences of angular momentum. In particular, its use to manipulate systems or to detect rotations is described. Finally, further developments and technological barriers are considered.

orbital angular momentum
rotational doppler effect
torque
rotation

The concept of linear momentum has been known since 1619, when Johannes Kepler attempted to explain why the tail of a comet always points away from the Sun [1]. The prediction that light carries linear momentum and can exert pressure on any surface it encounters was made by James Clerk Maxwell in 1862 [2], and was experimentally verified by Piotr Lebedev in 1900 [3], as well as independently by Edward Leamington Nichols and Gordon Ferrie Hull in 1901 ^[4][5][4,5]. Linear momentum has also been proposed for use in solar sails ^[6][7][6,7], following the ideas of Jules Verne in his 1865 book From the Earth to the Moon [8]. More recently, laser cooling ^[9][10][11][9,10,11] and optical trapping [12] have been based on the exchange of linear momentum.

Curiously, light can also carry angular momentum, either Spin Angular Momentum (SAM) or Orbital Angular Momentum (OAM), and can generate torques. Initial experiments involving SAM have been performed on macroscopic ^[13][14][15][13,14,15] and microscopic [16] systems. More recently, exchanges involving OAM have also been reported ^[17][18][19][17,18,19]. While OAM and SAM may be linked in tightly focused beams, they can be clearly separated within the paraxial approximation ^[20][21][22][20,21,22]. OAM may have further applications, for example, by offering new diversity in telecommunications ^[23][24][23,24]. The aim of this entry is to provide a comprehensive explanation of OAM and to explore several potential applications.