Parallel-plate ion trap useful for optical studies of microparticles

We report an electrodynamic ion trap composed of four disk electrodes with a hole at the center of each electrode. This ion trap has been developed in order to suspend single micrometer sized droplets. To levitate a droplet, an ac voltage was applied to the two middle electrodes, and the two end electrodes were used to form an additional dc field to balance the gravitational force on the droplet. By further applying compensating dc voltages to the rods which support the disks, the droplet could be maintained at the center of the ion trap with a positional fluctuation of less than 1 μm. It is shown here that this is useful for obtaining both spatial images and emission spectra of dye-doped droplets with higher spatial resolutions than those obtained in systems without such compensation.