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Design of an optical trap and calibration of its trap stiffness using the equipartition theorem
Umeå University, Faculty of Science and Technology, Department of Physics.
2016 (English)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

The aim of this work was to construct an optical tweezers instrumentation and to calibrate the stiffness of the system using the equipartition theorem. The beam expansion part of optical tweezers system was designed using Zemax. The trapping part of the system was built using various optics, among other things, a 0.36 mW He-Ne laser and an oil-immersion objective with numerical aperture (NA) of 1.3 for trapping of polystyrene bead with 1μm. The equipartition theorem was applied to calibrate the trap stiffness using position sensitive detector (PSD). The calibration coefficient was obtained by measuring the relative displacement recorded by the PSD with respect to the displacement of particle on the specimen plane in x and y direction. The stiffness we measured in x direction was (3.4±0.2) pN/μm, and in y direction was (4.0±0.1) pN/μm. By improving the alignment with a pin hole and making sure the center of the beam went through the objective, a symmetrical optical trap was achieved. And by preserving the laser power with using as fewer optics as possible to get larger trapping force, the 1μm bead was trapped.

Place, publisher, year, edition, pages
National Category
Atom and Molecular Physics and Optics
URN: urn:nbn:se:umu:diva-122047OAI: diva2:936816
Subject / course
Fysik C - Examensarbete
Available from: 2016-06-14 Created: 2016-06-14 Last updated: 2016-06-14Bibliographically approved

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