Anthracene Crystallization Induced by Single-Shot Femtosecond Laser Irradiation:  Experimental Evidence for the Important Role of Bubbles

A mechanism of femtosecond laser-induced crystallization was investigated using a supersaturated solution of anthracene. When a single-shot femtosecond laser pulse with a pulse energy above 3.1 μJ/pulse was shot into a sufficiently supersaturated solution, crystallization of anthracene was induced immediately after irradiation at the vicinity of the laser focal point. The threshold energy of the crystallization (3.1 μJ/pulse) was in agreement with that of laser-induced bubble formation, which was a sequential process after shockwave emission, cavitation bubble formation, and collapse. Sufficient supersaturation for crystallization decreased with an increase in the pulse energy. These results suggest that crystallization is triggered in the processes resulting in bubble formation. Furthermore, crystallization was enhanced at the surface of the bubble. The crystallization mechanism was completely different from that reported previously based on photochemical reactions or molecular alignment due to a strong optical field.