Look up computer generated holography! It is certainly possible to calculate a hologram of a letter which focuses at some different depth than the screen. Ther

Look up computer generated holography! It is certainly possible to calculate a hologram of a letter which focuses at some different depth than the screen. There are issues which arise from restricting the hologram to a real valued grid, like limited FoV and noise, but these are not impossible problems to solve and existing technology is already quite good in terms of image quality.