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 μm 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.
© 2006 Optical Society of America
Lasers and Laser Optics
Original Manuscript: April 11, 2005
Revised Manuscript: August 31, 2005
Manuscript Accepted: September 16, 2005
Vol. 1, Iss. 4 Virtual Journal for Biomedical Optics
Karen C. Vermeulen, Gijs J. L. Wuite, Ger J. M. Stienen, and Christoph F. Schmidt, "Optical trap stiffness in the presence and absence of spherical aberrations," Appl. Opt. 45, 1812-1819 (2006)