O-DOLS: On Demand Optically Levitated Sensors

The goal of this project is to demonstrate rapid loading of nanoparticles into optical traps under high vacuum to produce an on-demand optically levitated sensor (O-DOLS) for acceleration and electric field sensing. The O-DOLS prototype, designed during Phase I, includes both a single-beam optical tweezer and counterpropagating dual-beam trap for trapping nanoparticles of sizes ranging from 100 nm to 3 microns. Loading these traps will be accomplished using a piezo-driven launcher that releases nanoparticles from a glass substrate via mechanical vibration. During Phase I, we demonstrated trapping of a 100 nm silica nanoparticle with a single-beam optical tweezer under intermediate vacuum using this loading technique, but high vacuum is required during operation of the O-DOLS to reduce background gas damping to achieve a high mechanical quality factor and high sensitivity to acceleration and electric fields. During Phase II, we plan to demonstrate nanoparticle loading directly under high vacuum, which will drastically decrease the loading time by reducing or completely eliminating the time required to pump down to the operating pressure. This rapid loading will be accomplished using a triggered trap power ramp-up to trap nanoparticles in the absence of background gas damping, a slowing beam to reduce the speed of incoming nanoparticles below the escape velocity of the trap, and feedback cooling to stabilize the trapped nanoparticles under high vacuum. We will test the O-DOLS prototype at various pressures and device orientations to determine the overall loading time under the range of possible conditions, as well as characterize the acceleration sensitivity. Additionally, we will investigate charge control on the trapped nanoparticles using UV light and characterize the sensitivity to electric fields. The trapping location in the O-DOLS is designed to be free of nearby conducting surfaces except for two small tungsten wire electrodes for electrostatic force calibration and injection of electric fields, such as very low frequency radiation with frequencies ranging from 5 kHz to 50 kHz, to be sensed by a trapped charged nanoparticle. After testing the systems in the O-DOLS prototype, we will package all the components, including the vacuum chamber, electronics, image and data acquisition systems, and laser sources, on a portable platform to demonstrate mobile inertial measurements. We will also test this prototype for resilience to shock and vibration and evaluate failure modes, such as structural failure or misalignment of optics. The results of these tests will be used to refine systems and components to transition the prototype into a product for DAF and other end-users in anticipation of marketing the O-DOLS during Phase III.  Northwestern University will serve as the subcontractor of this project and test and optimize the various O-DOLS systems in collaboration with the prime contractor, Digital Optics Technologies, Inc.