It is intuitive to think that light interacts with matter but not with itself, that is that does not exist possibility of diffusion between two photons. Really the equations of classic electrodynamics, written in 1864 by Maxwell, that describe the light as an electromagnetic wave with frequencies in some steps, are linear in the electromagnetic field, in agreement with overlap principle. So it’s impossible for classic theory the diffusion between light beams.
But physicists soon understood that Maxwell’s description was incomplete. The quantum mechanics, with duality wave/particle, drove in 1920 to development of quantum electrodynamics (QED) by Dirac, Fermi, Schwinger, Feynman and Tomonaga. Exists a quantum non linearity of electromagnetic fields caused by the circumstance that uncertainty principle allows the momentary creation of a “virtual” couple electron – positron from two photons. This couple lives for a short time linked to the Heisemberg’s uncertainty principle and then annihilates emitting two others photons(inelastic diffusion). In other words light interacts only with matter, but for QED doesn't exist a space completely empty because virtual couples electron – positron are non stop created and immediately destroyed : vacuum is like a pot continuously boiling. These virtual particles of matter interact with photons giving out an effective non linearity of electromagnetic fields.
So remains open the problem if photons could interact with themselves in the absence of matter, that is in vacuum. In accord to actual scientific visions photons with highest frequencies (gamma rays), invisible to human eye, interact in vacuum when they have sufficient energy to generate a couple formed by an electron and its antiparticle, the positron. In this instance we don’t have deviation of beams in the crash, but the two ones simply disappear (into the "slang" annihilate) turning into matter (electron and positron exactly). This annihilating process really happens in the particle accelerators and in some astro physicians events.
In the theory exposed in this blog the inelastic diffusion of high frequency photons is due to the breaking of symmetrical interference of transversal sinusoidal waves (that generates stationary ones) with the consequential propagation of the incident waves at lower frequency.
This mechanism would be at the origin of vacuum “specific energy” expressed in Joule/m^3.