https://en.wikipedia.org/wiki/Coherent_addition
This is very interesting to the holographer, as it both provides high power and narrow linewidth!The addition of lasers reduces the number of longitudinal modes in the output beam; the more lasers are combined, the smaller is the number of longitudinal modes in the output. The simple estimates show that the number of output modes reduces exponentially with number of lasers combined.
Would this be feasible for a home-baked holography laser?