Improvements to Photophoretic Optical Trapping Based Holography Via Retroreflectors

Commercially available holographic technology is largely limited to 2D projection-based methods which have the disadvantage of limited viewing angles and low spatial bandwidth. Thus, there is a need for true 3D holograms which lack these issues. Recent research has shown that photophoretic optical trapping (POT), which involves using a focused laser to suspend a small reflective particle in midair, is an effective method for generating true 3D holograms by moving said particle rapidly in space to draw 3D images. However, this method suffers from two key drawbacks, a large power requirement for the laser (>48mW), and inconsistent trapping times for the suspended particle. Here, we investigate a more efficient configuration that re-uses scattered light from the laser to amplify the optical power at the particle trapping site, with the goal of increasing the length of time the particles remain suspended, i.e. particle trapping time. We choose to use retroreflectors to accomplish this task due to their key ability to reflect light parallel to its source without destructive interference. Particle trapping times using retroreflectors were compared against control setups without reflectors, as well as a setup that used mirrors instead of retroreflectors. We found that average trapping times with the retroreflectors had a threefold increase compared to without. It also has a consistently longer trapping time than any other test configuration, proving that retroreflector based POT setup is a viable low cost mechanism to improve the efficiency of POT-based holography.