Beth's experiment using optical tweezers

We show how a student may construct simple and versatile optical tweezers t o manipulate micron-sized particles. The tweezers apparatus is used to set birefringent calcite particles into rotation using circularly polarized lig ht. This demonstrates the mechanical transfer of the angular momentum assoc iated with circularly polarized light from the laser beam to the trapped pa rticle. This offers the student a method for performing Beth's experiment q ualitatively in the undergraduate laboratory. (C) 2001 American Association of Physics Teachers.