Absolute calibration of optical tweezers including aberrations

We extend a previous proposal for absolute calibration of optical tweezers by including optical setup aberrations into the first-principles theory, with no fitting parameters. Astigmatism, the dominant term, is determined from images of the focused laser spot. Correcting it can substantially increase stiffness. Comparison with experimental results yields agreement within error bars for a broad range of bead sizes and trap heights, as well as different polarizations. Absolute calibration is established as a reliable and practical method for applications and design of optical tweezers systems. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3699273]