Enhanced Predictability of Urea Crystallization by an Optimized Laser Repetition Rate.

Area of Science:

• * Physical Chemistry
• * Materials Science
• * Laser Physics

Background:

• * Laser-induced crystallization offers a novel approach to crystallizing organic molecules.
• * Precise control over experimental parameters is crucial for predictable outcomes.
• * The pulse repetition rate's influence on crystallization induction time is not well understood.

Purpose of the Study:

• * To investigate the impact of laser pulse repetition rate on the induction time of laser-induced crystallization.
• * To identify an optimal pulse repetition rate for efficient crystallization.
• * To understand the underlying mechanisms affecting crystallization efficiency at different repetition rates.

Main Methods:

• * Irradiating a supersaturated urea solution with near-infrared (1030 nm) laser pulses (5 ps duration, ~340 μJ energy).
• * Systematically varying the pulse repetition rate from 10 Hz to 20,000 Hz.
• * Measuring the time delay to crystallization initiation (induction time) and calculating the probability of successful crystallization events.

Main Results:

• * An optimal pulse repetition rate was identified between 500 Hz and 1 kHz, yielding median induction times of 2-5 seconds.
• * The mean probability of successful crystallization was highest in the optimal range (5 × 10⁻²%).
• * Higher repetition rates (5-20 kHz) significantly reduced crystallization probability (3 × 10⁻³%), likely due to thermocavitation bubble interactions.

Conclusions:

• * The pulse repetition rate is a critical parameter for controlling laser-induced crystallization.
• * An optimized pulse repetition rate enhances predictability and efficiency in crystallizing organic molecules.
• * Understanding pulse interactions, such as with thermocavitation bubbles, is essential for process optimization.