I see. I forgot that the shape of an electromagnetic wave depends on its wavelength as well. Thanks a lot!
Although, you could maintain coherency while combining the beams of lasers of the same wavelength, right?
What do you mean? Why does light need to be monochromatic in order to stay coherent? Does this mean that you couldn't combine the beams of red, green, and blue lasers to create a white laser, because white light is the sum of all wavelengths of light?