Luminescent nanoparticle trapping with far-field optical fiber-tip tweezers
Résumé
We report stable and reproducible trapping of luminescent dielectric YAG:Ce3+ nanoparticles with sizes down to 60 nm using far-field dual fiber tip optical tweezers. The particles are synthesized by a specific glycothermal route followed by an original protected annealing step, resulting in significantly enhanced photostability. The tweezers properties are analyzed by studying the trapped particles residual Brownian motion using video or reflected signal records. The trapping potential is harmonic in the transverse direction to the fiber axis, but reveals interference fringes in the axial direction. Large trapping stiffnesses of 35 and 2 pN µm-1 W-1 are measured for a fiber tip-to-tip distance of 3 µm and 300-nm and 60-nm particles, respectively.
The forces acting on nanoparticles are discussed within the dipolar approximation (gradient and scattering force contributions) or exact calculations using the Maxwell Stress Tensor formalism. Prospects for trapping even smaller particles are discussed.