After viewing this: My Homemade 40W Laser Shotgun
Will the initial 40W power of the diodes beams be roughly transferred to the targeted surface where the 8 beams are focused, or will there be a power loss due to some kind of interferences where the beams overlap?
If energy is lost, it must go somewhere. So, there won't be any "interference" where the beams overlap which saps the power. Unless, and this does happen, the lasers are powerful enough to ionize the air, in which case the light is blocked at that point and converted to heat, which will never make it to the surface. See this article on laser-induced breakdown.
I doubt the contraption in question has the power-density to do this, though.
