Methods to directly measure the trapping potential in optical tweezers

Techniques to measure the trapping force in an optical tweezers without any prior assumptions about the trap shape have been developed. The response of a trapped micro or nanoparticle to a step input is measured and then used to calculate the trapping force experienced by the particle as a function of it's position in the trap. This method will provide new insight into the trapping behavior of nanoparticles, which are more weakly bound than microparticles and thereby explore larger regions of the trapping potential due to Brownian motion. Langevin dynamics simulations are presented to model the system and are used to demonstrate this technique. Preliminary experimental results are then presented to validate the simulations. Finally, the measured trapping forces, from simulations and laboratory experiments, are integrated to recover the trapping potential.