Calibration and characterization of static and modulated optical traps

As optical tweezers become widely used in biophysics, calibration becomes essential to quantitatively characterize the dynamics of a system probed by this technique. In this thesis, I apply three methods for calibrating optical tweezers: a direct estimate from thermal motion of a trapped particle using the equipartition theorem, a more advanced approach that analyzes its power spectrum, and a combination of power spectrum analysis and the bead’s response under an external driving force. Motivated by recent attempts to use parametric resonance for calibration, I also examine the effects of modulating laser power on the motion of the trapped particle, predicting and finding experimentally an increase in the particle’s position variance at low modulation frequencies without evidence for resonant effects in the extremely overdamped motion of the trapped particle. I conclude by discussing future considerations such as the treatment of hydrodynamics and the effect of an anharmonic trap potential.