The impact of femtosecond (fs) laser ablation on the shape and nonlinear optical (NLO) properties of organic crystals was investigated. fs laser ablation of a local region of a NLO crystal can selectively enhance the growth of targeted faces. Reflection imaging of crystal surfaces revealed that a number of new crystal steps are generated from ablated area, which induces the crystal growth enhancement. In addition, the evaluation of terahertz wave emission from ablated crystals shows that NLO properties are not deteriorated after fs laser ablation. We foresee that crystal shape control by such a damage-less ablation process will potentially improve the NLO properties of organic crystals.
In this work, laser ablation-induced crystallization of a single-component system was demonstrated using a melt of glacial acetic acid. We systematically investigated the dependence of the crystallization probability on laser energy, pulse duration, and beam profile. We also monitored other laser ablation-induced phenomena, cavitation bubble generation, and temperature elevation, which also depend on those laser parameters. We found that the tendency of crystallization probability can be qualitatively interpreted by the interplay between positive (size of cavitation bubble) and negative (temperature elevation) factors, which provides fundamental insights into the underlying mechanism of laser ablation-induced crystallization.
Focused irradiation with ultrashort laser pulses realized
the fine
spatiotemporal control of ice crystallization in supercooled water.
An effective multiphoton excitation at the laser focus generated shockwaves
and bubbles, which acted as an impulse for inducing ice crystal nucleation.
The impulse that was localized close to the laser focus and accompanied
by a small temperature elevation allowed the precise position control
of ice crystallization and its observation with spatiotemporal resolution
of micrometers and microseconds using a microscope. To verify the
versatility of this laser method, we also applied it using various
aqueous systems (e.g., plant extracts). The systematic study of crystallization
probability revealed that laser-induced cavitation bubbles play a
crucial role in inducing ice crystal nucleation. This method can be
used as a tool for studying ice crystallization dynamics in various
natural and biological phenomena.
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