  The properties of four-wave interaction via the nonlinear quantum vacuum is
investigated. The effect of the quantum vacuum is to generate photons with new
frequencies and wave vectors, due to elastic photon-photon scattering. An
expression for the number of generated photons is derived and using
state-of-the-art laser data it is found that the number of photons can reach
detectable levels. In particular, the prospect of using the high repetition
Astra Gemini system at the Rutherford Appleton Laboratory is discussed. The
problem of noise sources is reviewed, and it is found that the noise level can
be reduced well below the signal level. Thus, detection of elastic
photon-photon scattering may for the first time be achieved.
