Beth’s experiment using optical tweezers

Abstract

We show how a student may construct simple and versatile optical tweezers to manipulate micron-sized particles. The tweezers apparatus is used to set birefringent calcite particles into rotation using circularly polarized light. This demonstrates the mechanical transfer of the angular momentum associated with circularly polarized light from the laser beam to the trapped particle. This offers the student a method for performing Beth’s experiment qualitatively in the undergraduate laboratory.