  In contrast to wave functions in nonrelativistic quantum mechanics
interpreted as probability amplitudes, wave functions in relativistic quantum
mechanics have generalized meanings such as charge-density amplitudes,
energy-density amplitudes as well as particle-number density amplitudes, etc.
Applying electromagnetic field intensities we construct a photon wave function,
it corresponds to the (1,0)+(0,1) spinor representation of the electromagnetic
field, and can be interpreted as the energy-density amplitude of photons
outside a source. In terms of photon wave functions we develop photon wave
mechanics, which provides us with a new quantum-mechanical description for
photons outside a source.
