Direct measurement of the skew angle of the Poynting vector in a helically phased beam

Abstract

Abstract:We measure the local skew angle of the Poynting vector within a helically-phased, exp ilφ ( ) , beam using a Shack Hartmann wavefront sensor.It is the skew angle of the Poynting vector with respect to the beam axis that gives rise to the orbital angular momentum of a light beam. We confirm that this skew angle is l kr , corresponding to an orbital angular momentum of l per photon. Measurement of orbital angular momentum in this way is an alternative to interferometric techniques giving a non-ambiguous result to both the magnitude and sign of l from a single measurement, without any restriction on the optical bandwidth.

Orbital angular momentum: origins, behavior and applications

“…At a radius r, the inclination of the phase front, and hence of the Poynting vector, with respect to the beam axis is simply λ/2πr. This, in turn, sets the azimuthal component of the light's linear momentum ashk 0 λ/2πr per photon [5], which, when multiplied by the radius vector, gives an angular momentum of h per photon [6]. For comparison, we note that a circular path of circumference λ has a radius of λ/2π.…”

Refractive elements for the measurement of the orbital angular momentum of a single photon

“…The optical transformation we utilise is only perfect for rays which are normally incident on the transformation elements. Helically phased beams are inherently not of this type, and have a skew angle of the rays of θ s = /kr, where k is the wavenumber of the light and r is the distance from the beam centre [22,23]. A numerical simulation of the experimental setup was carried out using plane wave decomposition [14].…”

Detection of a spinning object using lights orbital angular momentum

“…The angle between the Poynting vector and the beam axis is = 2 , where is the radius from the beam axis [15] (Fig. 1B).…”