  Radiation pressure forces in a focussed laser beam can be used to trap
microscopic absorbing particles against a substrate. Calculations based on
momentum transfer considerations show that stable trapping occurs before the
beam waist, and that trapping is more effective with doughnut beams. Such
doughnut beams can transfer angular momentum leading to rotation of the trapped
particles. Energy is also transferred, which can result in heating of the
particles to temperatures above the boiling point of the surrounding medium.
