Optical trappings of ThO2 and UO2 particles using radiation pressure of a visible laser light

Optical trappings of ThO2 and UO2 particles have been first demonstrated in water using the radiation pressure of a TEM(00)-mode He-Ne laser beam of lambda=633 nm. It was observed that a ThO2 particle was successfully trapped three-dimensionally in the focus region and transferred by moving the focus. On the other hand, for a UO2 particle of which a refractive index and an extinction coefficient are relatively large in the visible region, only two-dimensional trapping was observed when the beam focus was located near the bottom of the particle. One of the main difficulties in the optical trapping of nuclear fuel particles is attributed to their relatively large absorption coefficients in the visible region. Computational studies on three-dimensional optical trapping performances of absorbing particles were, therefore, performed with a simulation code based geometrical optics. The present calculation can well predict the experimental results on the optical trapping characteristics for ThO2 and UO2 particles.