  The photon is modeled as a monochromatic solution of Maxwell's equations
confined as a soliton wave by the principle of causality of special relativity.
The soliton travels rectilinearly at the speed of light. The solution can
represent any of the known polarization (spin) states of the photon. For
circularly polarized states the soliton's envelope is a circular ellipsoid
whose length is the observed wavelength ($\lambda$), and whose diameter is
$\lambda/\pi$; this envelope contains the electromagnetic energy of the wave
($h\nu=hc/\lambda$). The predicted size and shape is confirmed by experimental
measurements: of the sub-picosecond time delay of the photo-electric effect, of
the attenuation of undiffracted transmission through slits narrower than the
soliton's diameter of $\lambda/\pi$, and by the threshold intensity required
for the onset of multiphoton absorption in focussed laser beams. Inside the
envelope the wave's amplitude increases linearly with the radial distance from
the axis of propagation, being zero on the axis. Outside the envelope the wave
is evanescent with an amplitude that decreases inversely with the radial
distance from the axis. The evanescent wave is responsible for the observed
double-slit interference phenomenon.
