TY - JOUR
T1 - Mechanical Evidence of the Orbital Angular Momentum to Energy Ratio of Vortex Beams
A1 - Demore,Christine E. M.
A1 - Yang,Zhengyi
A1 - Volovick,Alexander
A1 - Cochran,Sandy
A1 - MacDonald,Michael P.
A1 - Spalding,Gabriel C.
AU - Demore,Christine E. M.
AU - Yang,Zhengyi
AU - Volovick,Alexander
AU - Cochran,Sandy
AU - MacDonald,Michael P.
AU - Spalding,Gabriel C.
PY - 2012
Y1 - 2012
N2 - We measure, in a single experiment, both the radiation pressure and the torque due to a wide variety of propagating acoustic vortex beams. The results validate, for the first time directly, the theoretically predicted ratio of the orbital angular momentum to linear momentum in a propagating beam. We experimentally determine this ratio using simultaneous measurements of both the levitation force and the torque on an acoustic absorber exerted by a broad range of helical ultrasonic beams produced by a 1000-element matrix transducer array. In general, beams with helical phase fronts have been shown to contain orbital angular momentum as the result of the azimuthal component of the Poynting vector around the propagation axis. Theory predicts that for both optical and acoustic helical beams the ratio of the angular momentum current of the beam to the power should be given by the ratio of the beam’s topological charge to its angular frequency. This direct experimental observation that the ratio of the torque to power does convincingly match the expected value (given by the topological charge to angular frequency ratio of the beam) is a fundamental result.

© 2012 American Physical Society

AB - We measure, in a single experiment, both the radiation pressure and the torque due to a wide variety of propagating acoustic vortex beams. The results validate, for the first time directly, the theoretically predicted ratio of the orbital angular momentum to linear momentum in a propagating beam. We experimentally determine this ratio using simultaneous measurements of both the levitation force and the torque on an acoustic absorber exerted by a broad range of helical ultrasonic beams produced by a 1000-element matrix transducer array. In general, beams with helical phase fronts have been shown to contain orbital angular momentum as the result of the azimuthal component of the Poynting vector around the propagation axis. Theory predicts that for both optical and acoustic helical beams the ratio of the angular momentum current of the beam to the power should be given by the ratio of the beam’s topological charge to its angular frequency. This direct experimental observation that the ratio of the torque to power does convincingly match the expected value (given by the topological charge to angular frequency ratio of the beam) is a fundamental result.

© 2012 American Physical Society

U2 - 10.1103/PhysRevLett.108.194301
DO - 10.1103/PhysRevLett.108.194301
M3 - Article
JO - Physical Review Letters
JF - Physical Review Letters
SN - 0031-9007
IS - 19
VL - 108
SP - -
ER -