Abstract
A glass microbubble (diameter ∼15 μm, wall 0.65 μm) was levitated in high vacuum by an actively controlled electric field. While held vertically, the particle moved freely in the horizontal plane under the influence of a central restoring force. The Brownian motion of the particle was observed and quantified by successive measurements of the oscillation amplitude in a horizontal axis. Brownian motion was exhibited throughout the pressure range from 7×10−6 to 7×10−4 Torr. The statistical behavior of the oscillation amplitude is consistent with the theoretical prediction for Brownian motion in a low pressure gas. These measurements constitute the first direct observation of Brownian motion of a levitated particle in an environment below 1 Torr. In addition to the experimental verification of low pressure Brownian motion theory, this work serves as an important step in the development of a standardizing high vacuum gauge.
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