Dresden 2011 – scientific programme
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BP: Fachverband Biologische Physik
BP 32: Posters: Other Topics in Biological Physics
BP 32.4: Poster
Thursday, March 17, 2011, 17:15–20:00, P3
Under-filling trapping objectives optimizes the use of available laser power in optical tweezers — •Mohammed Mahamdeh1, Citlali Pérez Campos2, and Erik Schäffer1 — 1Nanomechanics Group, Biotechnology Center, TU Dresden, Tatzberg 47-51, 01307 Dresden, Germany — 2Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstraße 108, 01307 Dresden, Germany
For optical tweezers, especially when used in biological studies, optimizing the trapping efficiency reduces photo damage or enables the generation of larger trapping forces. One important parameter that affects the efficiency is the filling ratio—the laser beam width relative to the numerical aperture (NA) diameter that accords with Abbe’s sine condition. Here, we measured the optimal filling ratio for 0.5–2 µm diameter microspheres and compared the results to Mie theory calculations. We show that slightly under-filling a 1.3 NA objective with a filling ratio of 0.95 using 0.85 µm diameter microspheres resulted in the highest overall trapping efficiency. Under these conditions, the maximum trap stiffness is 30 % higher compared to a filling ratio of 1.3. The optimal filling ratio varied with microsphere size in the lateral but not in the axial direction. Our finding suggests that apart from the choice of optimal microsphere size, under-filling the objective is key for optimal performance of an optical trap.