W. H. Campos, T. A. Moura, O. J. B. J. Marques, J. M. Fonseca, W. A. Moura-Melo, M. S. Rocha, and J. B. S. Mendes
Oscillatory dynamics is a key tool in optical tweezer applications. It is usually implemented by mechanical interventions that cannot be optically controlled. In this paper, we show that germanium semiconductor beads behave as optically induced oscillators when subjected to a highly focused laser beam. In turn, the well-defined direction of oscillations can be manipulated by the polarization of the light beam. Such unusual motion is due to the competition between the usual optical forces and the radiometric force related to thermal effects, which pushes the beads from the focal region. We characterize the behavior of the germanium beads in detail and propose a model accounting for the related forces in good agreement with the experimental data. Such kind of system can potentially revolutionize the field of optical manipulation, contributing to the design of single molecule machines and to the application of oscillatory forces in fundamental physics, cellular manipulation, fluid dynamics, and other soft-matter systems.
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