The zero point field and the reduction of the wave packet in   semiclassical electrodynamics
  In the classical theory, an electromagnetic field obeying Maxwell's equations cannot be absorbed quickly by matter, so that it remains a zero point field. Splitting the total, genuine electromagnetic field into the sum of a conventional field and a zero point field is physically meaningless until a receiver attenuates the genuine field down to the zero point field, or studying the amplification of the zero point field by a source.   In classical optics all optical effects must be written using the genuine field, so that at low light levels the nonlinear effects become linear in relation to the conventional field. The result of the interpretation of all observations, even at low light levels, is exactly the same in quantum electrodynamics and in the semi- classical theory.   The zero point field is stochastic only far from the sources and the receivers; elsewhere, it is shaped by matter, it may be studied through fields visible before an absorption or after an amplification.   A classical study of the reduction of the wave packet extends the domain of equivalence of the classical and quantum zero point field; using both interpretations of this field makes the results more reliable, because the traps are different. 
Jacques Moret-Bailly