Circularly polarized light half wave plate

When circularly polarized light falls on a quartz half-wave plate in the shape of a disc, a torque is developed. The transmitted light is of the opposite circular polarization. The half-wave plate disc can rotate as it hangs on a thin quartz fibre, and the magnitude of the photon spin can be deduced from the torsion angle a. 

Schematic diagram showing the integration of a polarization modulated birefringence apparatus within a laser Doppler velocimeter. This shows the side view. L light source (a diode laser was used) PSG rotating half-wave plate design LS lens FC flow cell (flow is into the plane of the figure) CP circular polarizer D detector 2D-T two dimensional translation stage 3D-T three dimensional translation stage LDVP laser Doppler velocimeter probe.

It has been shown experimentally that a beam o circularly-polarized light exerts a torque on any optical component, such as a quarter- or half-wave plate, which changes the state of polarization of the light. This corresponds to a transfer of angular momentum from the radiation fields to the material system. To calculate the rate at which angular momentum is radiated by an electric dipole... 

Figure 5 DCP backscattering arrangement. A single quarter-wave plate can function In a circular polarizer and analyser configuration. True zero-order retarders may be placed ahead of the light collection lens, albeit with loss of precision. The plate Is rotated within 200 ms in the appropriate orientation and stopped during the data acquisition half-cycle.

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