Hi, I've had a introductory class to Photonics last year, and now we're elaborating on a few things in my class of Microphotonics. Apart from that, I've had classes about EM fields and all, - that's more or less my background regarding this matter. In both last year's and this year's course, we've briefly touched the topic of Holography. Very briefly. Too briefly to fully understand it. I find that a shame - holography is a pretty exciting application to encounter - and I was hoping to understand better what is written in my course about. So: a laser bundle is split by a half-mirror, they diverge in opposite directions (ie. the mirror is vertical, and the bundle hits it in an angle of 45 degrees). Then the two bundles are reflected both by mirrors, thus recombining them on a substrate with a photosensitive layer. We assume the laser bundle is TE-polarised. Because of the chosen polarisation both bundles have a parallel E field at the height of the surface and so they interfere. Now, my question is: why do they have to be TE-polarised? I don't know much about this - in most of my course we simply work with TE-polarised bundles, yet everywhere it is implicitly stated that TM-polarised waves behave more or less dual. I was wondering : why won't this holography setup work for TM-polarised bundles (if that's what they're implying)? Why not, and how would it have to be adjusted to work for TM-polarised bundles? Probably a dumb question,- I think I just need to realise the essential differences between TE and TM modes... I've seen it (the mathematics I mean), but I haven't been able to get a clear image in my head of the differences.