The role of turbulence in bottom-up nanoparticle synthesis using ultrafast laser filamentation in ethanol

Abstract Ultrafast laser filamentation in liquids based on nonlinear optical phenomenon is a new method for bottom-up nanoparticle synthesis. The process is able to synthesize nanomaterials such as nanodiamonds from the liquid precursor. However, the process occurs in a transparent liquid medium and the generation is limited to the interaction volume of the laser beam. In the current work, the effects of turbulence on ultrafast laser filamentation are investigated in an attempt to increase the generation rate. A fixed laser energy, at about ten times the threshold of filamentation in ethanol, is used to ensure persistent filamentation below the vaporization limit. Turbulence in the ethanol precursor was introduced by a high laser repetition rate, mechanical motion, and ultrasonication. The effects were investigated by absorbance measurements of the ethanol sample after laser filamentation, which correlates with the concentration of nanoparticles. For a fixed number of laser pulses, higher absorbance was observed on the sample prepared using a higher repetition rate (53% for 3 kHz compared to 1 kHz). The absorbance of the sample obtained by laser filamentation with cuvette motion increased by ∼22% compared to the stationary sample. Finally, when laser synthesis was performed with ultrasonication, the highest increase in absorbance was obtained (∼61%). The mechanisms that contributed to the increase are discussed.