Physicists at BYU have demonstrated a volumetric projection system that works by using a laser to unevenly heat single cellulose molecules in order to shove them around in 3D space, then painting the positioned molecules with lasers that cause them to glow; by choreographic both sets of lasers, extremely high-resolution moving images can be attained.
The system has one major drawback: it is extremely sensitive to any sort of breeze. The researchers plan on overcoming this by replacing the cellulose molecules with vapor mists.
The technique, described in Nature on 24 January, works more like a high-speed Etch a Sketch: it uses forces conveyed by a set of near-invisible laser beams to trap a single particle — of a plant fibre called cellulose — and heat it unevenly. That allows researchers to push and pull the cellulose around. A second set of lasers projects visible light — red, green and blue — onto the particle, illuminating it as it moves through space. Humans cannot discern images at rates faster than around 10 per second, so if the particle is moved fast enough, its trajectory appears as a solid line — like a sparkler moving in the dark. And if the image changes quickly enough, it seems to move. The display can be overlaid on real objects and viewers can walk around it in real space.
A photophoretic-trap volumetric display [D. E. Smalley, E. Nygaard, K. Squire, J Van Wagoner, J. Rasmussen, S. Gneiting, K. Qader, J. Goodsell, W. Rogers, M. Lindsey, K. Costner, A. Monk, M. Pearson, B. Haymore and J Peatross/Nature](Sci-Hub mirror)
Physicists create Star Wars-style 3D projections — just don't call them holograms [Elizabeth Gibney/Nature]
(via Beyond the Beyond)