Adaptive optics in an optical trapping system for enhanced lateral trap stiffness at depth
Authors: Müllenbroich M.C., McAlinden N., Wright A.J.
Autors Affiliation: Institute of Photonics, University of Strathclyde, Wolfson Centre, Rottenrow, 0106, G4 0NW Glasgow, United Kingdom; IBIOS, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
Abstract: In optical trapping systems the trap stiffness, or spring constant, deteriorates dramatically with trap depth due to optical aberrations and system misalignment. This can severely hamper studies that employ optical tweezers to make accurate quantitative measurements. Here, a deformable membrane mirror is used, in conjunction with a random search algorithm, to correct for these aberrations by optimizing on a merit factor that is directly proportional to the trap stiffness. Previous studies have sought to address this issue but none have used a merit factor that is directly proportional to the trap stiffness. We demonstrate that the lateral trap stiffness, measured with and without aberration correction at increasing depths, improves throughout the trapping range of a conventional trap and allows us to extend the maximum depth at which we can trap from 136 to 166 µm. At a depth of 131 µm, trap stiffness improved by factors of 4.37 and 3.31 for the x- and y-axes respectively. The aberration correction resulted in deformable membrane mirror shapes where a single shape could be applied throughout a wide range of trap depths, showing significant improvement, and had the added benefit of making the lateral trapping forces more uniform in x and y.
Journal/Review: JOURNAL OF OPTICS
Volume: 15 (7) Pages from: 075305 to: 075305
More Information: Engineering and Physical Sciences Research Council, EPSRC, EP/H024891/1. KeyWords: Aberration correction; Deformable membrane mirrors; Opticaltrapping; Quantitative measurement; Random search algorithm; Spring constants; Trap stiffness; Trapping forces, Aberrations; Adaptive optics; Optical tweezers, StiffnessDOI: 10.1088/2040-8978/15/7/075305