I've always wondered can 2 lasers that are invisible to human sight (eg: infrared or ultraviolet) interfere with each other to make visible light.,(reply>), There used to be a lab prototype of a holographic display. Two laser beams were infrared so invisible, and the 'dots' in the tank didn't interact.<br>   But when two beams struck at the same time, the 'dots' glowed.<br><br>(I say 'dots' because I don't recall what the emitters were. Close enough.)