From a practical standpoint, can we combine two (or more) lasers tuned to almost-but-not-quite identical frequencies to create distance-specific illumination? For instance, say we have a 1 micron laser and a 0.9999 micron laser which we combine through some beam-combiner optics. In theory I think this should create alternating constructive and destructive interference with a wavelength of (1 micron/(1 micron-0.9999 micron)) x 1 micron=1 cm. Therefore if we took a projection screen and moved it progressively further away from the laser aperture it should fluctuate between bright and completely dark images on a length scale of 1cm. I imagine that by adding more lasers (adding more sine waves) you could make the regions of brightness arbitrarily small and come up with very distance-specific illumination. But is this actually practical or are the material requirements too difficult? Perhaps at maser wavelengths?