  It is common to introduce optical tweezers using either geometric optics for
large particles or the Rayleigh approximation for very small particles. These
approaches are successful at conveying the key ideas behind optical tweezers in
their respective regimes. However, they are insufficient for modelling
particles of intermediate size and large particles with small features. For
this, a full field approach provides greater insight into the mechanisms
involved in trapping. The advances in computational capability over the last
decade has led to better modelling and understanding of optical tweezers.
Problems that were previously difficult to model computationally can now be
solved using a variety of methods on modern systems. These advances in
computational power allow for full field solutions to be visualised, leading to
increased understanding of the fields and behaviour in various scenarios. In
this paper we describe the operation of optical tweezers using full field
simulations calculated using the finite difference time domain method. We use
these simulations to visually illustrate various situations relevant to optical
tweezers, from the basic operation of optical tweezers, to engineered particles
and evanescent fields.
