  Oscillatory dynamics is a key tool in optical tweezers applications. It is
usually implemented by mechanical interventions that cannot be optically
controlled. In this work we show that Germanium semiconductor beads behave as
optically induced oscillators when subjected to a highly focused laser beam.
Such unusual motion is due to the competition between the usual optical forces
[1-3] and the radiometric force related to thermal effects, which pushes the
beads from the focal region [4]. 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. The well defined direction of
oscillations can be manipulated by the polarization of the light beam. Such
kind of system can potentially revolutionize the field of optical manipulation,
contributing to the design of single molecule machines and the application of
oscillatory forces in macromolecules and other soft matter systems.

Optics