Ellipsoidal Nanoparticles, Resonance, and Spinning

We model the optical frequency response of a dipolar ellipsoidal nanoparticle in water using the Drude model and predict its angular velocity under an applied optical field. The particle's angular velocity is computed as a function of two key parameters of the driving field: polarization ellipticity and frequency. Our results show that below a critical polarization ellipticity, the nanoparticle comes to a fixed equilibrium orientation, whereas over this threshold it experiences continuous rotation. Finally, we examine how this critical ellipticity depends on the frequency of the incident light.