Motion of an optically torqued nanorod: the overdamped case

A recent experiment [W. A. Shelton {\emph{et\ al.}}, Phys.\ Rev.\ E {\bf{71}}, 036204 (2005)] measured the response of a nanorod trapped in a viscous fluid to the torque produced by an incident optical frequency electromagnetic wave. The nonlinear differential equation describing this motion is similar that of a damped, driven pendulum. The overdamped limit of this equation has been solved analytically. We analyze the properties of this solution in comparison to the observations of the experiment and find very close agreement.