In optical manipulation experiments, the light force is provided by a laser beam, and objects ranging from a fraction of a nanometer, such as atoms, to 10s of micrometers, such as cells, are manipulated. Considering the ratio between the characteristic dimension L of the object and the wavelength λ of the trapping light, three different trapping regimes can be defined: (1) the Rayleigh regime, when L << λ; (2) the Mie regime, when L is comparable to λ; and (3) the geometrical optics regime, when L >> λ. Optical pulling forces emerge, under the appropriate circumstances, in the Mie regime.
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