Post History

Think about how that is supposed to work.  It seems you want two photons to somehow combine into a single photon and nothing else.  That means the output photon must have the combined energy of the two input photons because you've provided no other place for the energy to go.  And of course momentum needs to be conserved too.

However, a photon's momentum is also proportional to its energy.  But how is that supposed to work when the two photons aren't traveling in the same direction?  Take the extreme case of the two photons having equal energy but colliding head-on.  The net momentum is 0, but the net energy twice that of each photon.  You can't conserve both energy and momentum if the photons were allowed to combine.