We describe a way to determine the total angular momentum, both spin and
orbital, transferred to a particle trapped in optical tweezers. As an example
an LG02 mode of a laser beam with varying degrees of circular polarisation is
used to trap and rotate an elongated particle with a well defined geometry. The
method successfully estimates the total optical torque applied to the particle.
For this technique, there is no need to measure the viscous drag on the
particle, as it is an optical measurement. Therefore, knowledge of the
particle's size and shape, as well as the fluid's viscosity, is not required.Comment: 7 pages, 3 figure
