Abstract
Optical trappings of metallic oxide particles with various optical constants, GeO2, MgO, Al2O3, ThO2, Nd2O3, CeO2, TiO2 and UO2 have been experimentally performed in water using two kinds of visible laser lights and an objective lens of N.A. = 1.3. Two-dimensional optical trappings of all particles except UO2, which has a large extinction coefficient, were possible for either of the laser lights. On the other hand, while three-dimensional optical trapping was possible for CeO2 having a refractive index of -2.2 by a He-Ne laser light at 633nm, it was observed for particles having refractive index of ≤ 1.7 by an Ar+ laser light at 488nm. The trapping efficiencies of absorbing particles were calculated based on a geometrical optics model to determine the range of the complex index of refraction for which three-dimensional optical trapping is possible to take place. Calculational results have a fairly good agreement with experimental results.
