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9 February 2006 Optical tweezers 3D photonic force spectroscopy
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Since optical tweezers trapped microspheres can be used as an ultrasensitive force measurements technique, the knowledge of its theoretical description is of utmost importance. However, even the description of the incident electromagnetic fields under very tight focusing, typical of the optical trap, is not yet a closed problem. Therefore it is important to experimentally obtain whole accurate curves of the force as a function of wavelength, polarization and incident beam 3D position with respect to the center of the microsphere. Theoretical models for optical forces such as the Generalized Lorenz-Mie theory, can then be applied to the precisely evaluated experimental results. Using a dual trap in an upright standard optical microscope, one to keep the particle at the equilibrium position and the other to disturb it we have been able to obtain these force curves as a function of x, y and z position, incident beam polarization and also wavelength. Further investigation of optical forces was conducted for wavelengths in and out Mie resonances of the dielectric microspherical cavities for both TM and TE modes.
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Antonio A. R. Neves, Adriana Fontes, Wendel L. Moreira, André A. de Thomaz, Diogo B. de Almeida, Luiz C. Barbosa, and Carlos L. Cesar "Optical tweezers 3D photonic force spectroscopy", Proc. SPIE 6131, Nanomanipulation with Light II, 61310F (9 February 2006);

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