Here's a little something more about light interacting with light.
"groups of three photons interacting and, in effect, sticking together to form a completely new kind of photonic matter"
"the researchers found that the bound photons actually acquired a fraction of an electron’s mass. These newly weighed-down light particles were also relatively sluggish, traveling about 100,000 times slower than normal noninteracting photons"
Here's the article:
and the corresponding paper