A DIY hologram project based on AIRR ("Aerial Imaging by Retro‐Reflection") developed by Prof. Yamamoto. Using two optical component, if you count the observers eyes it's one more :D, this optical system can refocus light sources in mid air, hence you get the impression of a floating image in mid air. The main optical components are a half mirror (aka magic mirror) and a retroreflector. A retroreflector is like a mirror, but it reflects always the photons back to the light sources. For example, all the street signs utilises retroreflectors as a foil to get higher visibility. A similar foil is used for this project, but with a better optical resolution and reflectivity value. The half mirror is self made. The glas is cut from a photo picture frame, and a sun shield / privacy foil was applied.
http://www.k2.t.u-tokyo.ac.jp/perception/AIRR_Tablet/index-e.html
https://onlinelibrary.wiley.com/doi/abs/10.1002/j.2168-0159.2013.tb06364.x