Ultra-Thin Film Creates Vivid 3D Images with Large Field of View

looks fundamentally similar to a scratch hologram: https://www.youtube.com/watch?v=0uko9oixijg

It's a nanoscale form of plenoptic imaging. You can type that search term in YouTube to see large scale DIY versions of the principle. Typically you have a sheet tiled with tiny lenses, each of which acts as a kind of angle-dependent pixel. A 1-dimensional version of this principle can be seen in "lenticular" images, which are the ridged plastic 3d "holograms" you sometimes get in gift shops. In the case of this paper, they've done some funky lithography stuff and made ultra-tiny reflective mirrors, instead of chunky plastic refractive lenses.

A downside to making the "lenses" this small is the physics of diffraction. The precision with which you can steer a "beam" of light (actually a propagating wavefront) is directly proportional to the size of the thing you're steering it with - hence why JWST has such an enormous mirror. This is probably why they say the limit of "projection" is 8cm - deep projection demands high angular precision, and probably their system gets blurry very quickly the further from the film you try and project something.