This isn't optical interference (in which beams with different wavelengths couldn't affect each other, as you say). Instead, the recording media has a response

This isn't optical interference (in which beams with different wavelengths couldn't affect each other, as you say). Instead, the recording media has a response that looks kinda like intensity(lambda1) - intensity(lambda2). Then they combine a spot (bigger than they want) of wavelength lambda1, with a "doughnut" of wavelength lambda2. The net response of the recording media is then "spot minus doughnut" and if they choose the parameters right that looks sufficiently like a smaller spot. You can see the full article at http://www.nature.com/ncomms/2013/130619/ncomms3061/full/ncomms3061.html http://www.nature.com/ncomms/2013/130619/ncomms3061/full/nco... for more details.