Laser trapping at solution surface enabling optical control of crystal growth

Abstract

When single beam optical trapping is carried out at the air/solution interface, molecular or colloidal assembly with an ordered structure is formed and grown up outwardly from the focal spot. As the example, this paper shows L-phenylalanine crystallization under optical trapping at solution surface of the unsaturated solution. Single anhydrous plate-like crystal is formed from the focal spot, and its growth rate is controlled by tuning the laser power. It is considered that optical trapping at the crystal edge has a critical role in this crystal growth control. The crystal is surrounded with a dense domain consisting of the liquid-like clusters and solvent molecules. The clusters are trapped at the crystal edge where optical potential is formed through light propagation inside the crystal. The amount of the clusters to be trapped is possibly dependent on the incident laser power, resulting in the growth rate control. This “optical evolution” in assembly formation using optical trapping will provide new perspectives in designing novel bottom-up molecular and colloidal assemblies.