We explore a number of diffractive structures for simultaneous trapping of particles in photophoretic traps for free space volumetric displays. Current optical trap displays move a single particle along a complicated path; to scale displays from 1 cm^3 to 100 cm^3 we aim to move multiple particles along a simple path. Preliminary results for two diffractive approaches are reported: i) a low-order binary grating, and ii) a Fresnel lens. Results are given for trap rate (N=50) for carbon particles at standard pressure and temperature.

In this work we report an improved platform for testing and comparing particles for use in optical trap displays. We constructed seven prototypes, and deployed them to five different locations where they were successfully used to perform comparative optical particle trap tests. This improved rig makes it possible to expand optical trap display research by a decentralized group of citizen scientists.