Abstract
Photothermal convection has been a major obstacle for stable particle trapping in plasmonic optical tweezer at high optical power. Here we demonstrate a strategy to suppress the plasmonic photothermal convection by using near zero thermal expansion coefficient of water at low temperature. A simple square nanoplasmonic array is illuminated with a loosely Gaussian beam to produce two dimensional optical lattice for trapping of nanoparticle. We observe stable particle trapping due to near-field optical gradient forces at elevated optical power at low temperature. In contrast, at the sample optical power at room temperature, the particles will get expelled, and disappear once they enter into the optical lattice. This technique will greatly increase usable optical power and enhance the trapping capability of plasmonic optical tweezer.