Supercontinuum trap stiffness measurement using a confocal approach

We report a novel method for characterizing the stiffness of white light supercontinuum tweezers, in which the nonlinear photonic crystal fiber used for supercontinuum generation is also utilized as an effective confocal pinhole to track the motion of a trapped bead and as a scan head to realize rapid scanning of the optical trap. By measuring the phase of the bead's motion in following the trap, a lateral stiffness value of about 7.9 μN/m was obtained with supercontinumm power of about 75mW. Our technique can potentially allow for trap stiffness calibration along an arbitrary direction in three dimensions.