  Codes were written to simulate the propagation of monochromatic light through
a bare optical resonator, using a computational Fourier method to solve the
Huygens-Fresnel integral. This was used, in the Fox-Li method, to find the
lowest-loss eigenmodes of arbitrary cavity designs. An implicit shift `hopping'
method was employed to allow a series of increasingly higher-loss eigenmodes to
be found, limited in number by computational time.
  Codes were confirmed in their accuracy against the literature, and were used
to investigate a number of different cavity configurations.
  In addition to confirming the fractal nature of eigenmodes imaged at the
conjugate plane of a symmetric (g<-1) resonator, an initial study was made of
how the (imperfect) quality of the fractal fit varied as the defining aperture
was moved around the cavity.
  A comparison was also made with the fractal-patterns produced by codes
written to simulate basic video-feedback.
