Spatial control of crystal nucleation in agarose gel.

Spatial and temporal control of crystal nucleation is demonstrated by nonphotochemical laser-induced nucleation of an aqueous agarose gel prepared with supersaturated potassium chloride. The location of nucleation was controlled by means of an optical mask; crystals were only observed in the area exposed to near-infrared laser radiation. The dependence of nucleation on laser power was measured, and the results suggest that the agarose gel reduces the effective supersaturation of the aqueous potassium chloride.