Let's assume I can generate two individual light beams, one centered at a wavelength of 800nm (visible) and the other at 3450 nm (infrared). Obviously the visible light has a higher frequency than the infrared light. Since all EM waves travel at the speed of light, how can one achieve temporal overlap of two different light frequencies? I'm thinking that one must delay one of the light beams, but I'm uncertain of the correct equations to use to show this. Thanks in advance.