So I have a couple of cheap <5mw red laser modules. And I also have mirrors. And I'm bored. You can guess what happens next (profit). Some really strange effects that I'd love to know the origin of: 1.) The speckle effect from the laser beams - it doesn't actually matter where your eyes are focused, you will still see it clearly. Which suggests that the interference is created on the retina itself. How the heck? 2.) I have 2 modules, with a hole and a sort of vertical knurling around the top (for grip and to adjust focus). Let's label them X and Y, X is turned on, Y remains powered off. I position X such that half the aperture is blocked by the tip of Y. I get a vertical beam projected instead, not unlike a barcode scanner. There are, I believe, three points of high intensity - one directly from the aperture, another halfway across the "line" and another at the end of the "line". After this third 'point' the beam splits up. Crappy diagram here. 3.) Shining a laser at itself in the mirror (running it in square beam mode to get the most visible pattern) - A diagram shows this best. Of course, the interference pattern emerges exactly where the laser light meets with light from the "virtual laser". This is the strangest one, I heard (on here, most likely) that Paul Dirac held the belief that photons could only interfere with themselves (since annihilation is quite silly). How can you really say that about this case when it seems that there are two classical paths, one taking a slightly longer time than the other (i.e. reflection off the silver coating vs partial reflection off the glass front)?