TY - JOUR TI - Optical trap stiffness in the presence and absence of spherical aberrations. AU - Vermeulen, Karen C. AU - Wuite, Gijs J. L. AU - Stienen, Ger J. M. AU - Schmidt, Christoph F. T2 - Applied optics AB - Optical traps are commonly constructed with high-numerical-aperture objectives. Oil-immersion objectives suffer from spherical aberrations when used for imaging in aqueous solutions. The effect of spherical aberrations on trapping strength has been modeled by approximation, and only a few experimental results are available in the case of micrometer-sized particles. We present an experimental study of the dependence of lateral and axial optical-trap stiffness on focusing depth for polystyrene and silica beads of 2 microm diameter by using oil- and water-immersion objectives. We demonstrate a strong depth dependence of trap stiffness with the oil-immersion objective, whereas no depth dependence was observed with the water-immersion objective. DA - 2006/03/10/ PY - 2006 VL - 45 IS - 8 SP - 1812 EP - 1819 J2 - Appl Opt LA - eng SN - 1559-128X 1559-128X ER -