How Pulse Width Affects Laser Ablation of Organic Liquids

Laser synthesis in liquids is oftencarried out in organic solventsto prevent oxidation of metals during nanoparticle generation andto produce tailored carbon-based nanomaterials. This work investigateslaser ablation of neat organic liquids acetone, ethanol, n-hexane, and toluene with pulse widths ranging from 30 fs to 4 psthrough measurements of reaction kinetics and characterization ofthe ablation products with optical spectroscopy and mass spectrometry.Increasing the pulse width from 30 fs to 4 ps impacts both the reactionkinetics and product distributions, suppressing the formation of solventmolecule dimers and oxidized molecules while enhancing the yieldsof gaseous molecules, sp-hybridized carbons, andfluorescent carbon dots. The observed trends are explained in thecontext of established ionization mechanisms and cavitation bubbledynamical processes that occur during ultrashort pulsed laser ablationof liquid media. The results of this work have important implicationsboth for controlling the formation of carbon shells around metal nanoparticlesduring the ablation of solid targets in liquid and producing carbonnanomaterials directly from the ablation of organic liquids withouta solid target.