Brownian motion in a modulated optical trap

Motivated by recent attempts to use parametric resonance to calibrate the spring constant of a Brownian particle in an optical trap, we have looked systematically at the effects of modulating laser power on the motion of the trapped particle. We predict and find experimentally an increase in the particle's position variance at low laser modulation frequencies, but we find no evidence for any resonant effects in the extremely overdamped motion of the trapped particle. Our results can serve as a guide for designing multiple traps by the 'time-sharing' method.