We present an optical tweezer based study of rotation of microscopic objects
with shape asymmetry. Thermal fluctuations and rotations are simultaneously
monitored through laser back scattering. The rotation results in a modulation
in intensity of the back scattered light incident on a quadrant photo detector.
This results in the manifestation of peaks at a fundamental rotational
frequency and at integer harmonics, superimposed on a modified Lorentzian in
the power spectrum. The multiple peaks indicate that the rotations are periodic
but with varying angular velocity. We demonstrate the use of video microscopy
for characterization of low reflectivity rotors, such as biological cells. The
methods also enable a measurement of the average torque on the rotor, and in
principle, can reveal information about its principal moments of inertia, and
the role of hydrodynamics at micron levelsComment: 9 Pages, 6 Figure
