9 research outputs found
Mechanical Evidence of the Orbital Angular Momentum to Energy Ratio of Vortex Beams
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
"Gauging" the Fluid
A consistent framework has been put forward to quantize the isentropic,
compressible and inviscid fluid model in the Hamiltonian framework, using the
Clebsch parameterization. The naive quantization is hampered by the
non-canonical (in particular field dependent) Poisson Bracket algebra. To
overcome this problem, the Batalin-Tyutin \cite{12} quantization formalism is
adopted in which the original system is converted to a local gauge theory and
is embedded in a {\it canonical} extended phase space. In a different reduced
phase space scheme \cite{vy} also the original model is converted to a gauge
theory and subsequently the two distinct gauge invariant formulations of the
fluid model are related explicitly. This strengthens the equivalence between
the relativistic membrane (where a gauge invariance is manifest) and the fluid
(where the gauge symmetry is hidden). Relativistic generalizations of the
extended model is also touched upon.Comment: Version to appear in J.Phys. A: Mathematical and Genera