Pseudopolymorphism of Sodium Acetate in Supersaturated Aqueous Solution Induced by Focused Irradiation with Ultrashort Laser Pulses

We systematically studied pseudopolymorphism (anhydrate- and trihydrate-form) of sodium acetate induced by focused irradiation with ultrashort laser pulses into a supersaturated aqueous solution. We found that both anhydrate and trihydrate crystals were obtained with femtosecond (fs) laser pulses, while anhydrate crystals were preferentially generated with picosecond (ps) laser pulses. In addition, the maximum value of the crystallization probability with femtosecond laser pulses (∼100%) was higher than that with picosecond laser pulses (∼60%). We found that the laser parameter dependence of the crystallization behavior of sodium acetate can be well explained from a viewpoint of the temperature–concentration diagram of sodium acetate and the interplay of cavitation bubble generation (promoting nucleation) and temperature elevation (suppressing nucleation). We foresee that this study can provide basic insights into the underlying mechanism of the laser-induced pseudopolymorphism, which can allow for the optimization of laser parameters for the fine-tuned control of crystallization from aqueous solutions.