M.Sc Thesis
M.Sc Student Shahar Hirshfeld Proving the Relation of Angular Momentum and Number of Photons in a Beam with Angular Momentum Department of Physics Professor Emeritus Lipson Stephen

Abstract

Light has momentum which is carried by the photons. By deforming the phase of the light to that of a helical shape, the light can obtain an angular momentum around the center of the helical axis. A different way for the light to obtain an angular momentum is by polarizing it in a circular polarization. The first contribution to the angular momentum is the orbital angular momentum. Where, the second one is the spin angular momentum.

The goal of this work was to quantitatively evaluate the torque of a light beam with only orbital angular momentum. In contrast to other experiments where the orbital angular momentum was observed but not quantitatively evaluated.

In our set up we used low cost spiral phase filter with very high efficiency to give a diode laser light orbital angular momentum. This filter was made from a broken piece of Perspex that was deformed near the crack to achieve the desired phase. We obtained the orbital angular momentum order by measuring the phase of the wave using a simple Mach-Zehnder interferometer.

After that, the light beam was absorbed by a levitated magnet and rotated it. To levitate the magnet we used the combine force of a magnet and a diamagnet to create a stable equilibrium point. The rotation of the magnet was tracked by using a probe laser and charge-coupled device (CCD).

The result of the experiment was to confirm that the orbital angular momentum of a photon in a spiral wave with order m is mh/2p(0.976?0.004?0.277) where the first error is the random one and the second one is the systematic.