  Light that carries linear or angular momentum can interact with a mechanical
object giving rise to optomechanical effects. In particular, a photon transfers
its intrinsic angular momentum to an object when the object either absorbs the
photon or changes the photon polarization, as in an action/reaction force pair.
Here, we present the implementation of light-induced selective resonant driving
of the torsional mechanical modes of a single-mode tapered optical nanofiber.
The nanofiber torsional mode spectrum is characterized by polarimetry, showing
narrow natural resonances (Q$\approx$2,000). By sending amplitude modulated
light through the nanofiber, we resonantly drive individual torsional modes as
a function of the light polarization. By varying the input polarization to the
fiber, we find the largest amplification of a mechanical oscillation (>35 dB)
is observed when driving the system with light containing longitudinal spin on
the nanofiber waist. These results present optical nanofibers as a platform
suitable for quantum spin-optomechanics experiments.
