Coupling effects in position observations due to residual misalignments of imaging axes in counter-propagating dual-beam optical traps

Video microscopy is one of the most versatile and successful measurement techniques in the spatio-temporal characterization of particle manipulations. The orientations of the imaging axes are always manually aligned correspondingly to the axes of the optical traps. We assume a residual misalignment angle as 5° exists between one imaging axis and the optical axis. Generous repeated position fluctuations resulted from Brownian motion are simulated, and the statistical results demonstrate dramatic cross-coupling effects occur in the situation of inconsistent trapping stiffness in orthogonal axes. The coupling effects may cause biased stiffness estimations and deteriorate the accuracy of parameter measurements related to position observations. For misalignment calibrations, multi-position observation methods using power imbalance and optical binding interactions are proposed with detailed discussions. The calibration can help to improve the accuracy of position related parameter measurements using suspended particles.