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1. The effect of pulse duration on nanoparticle generation in pulsed laser ablation in liquids: insights from large-scale atomistic simulations

   https://doi.org/10.1039/D0CP00608D  

   Shih, Cheng-Yu; Shugaev, Maxim V.; Wu, Chengping; Zhigilei, Leonid V. (April 2020, Physical Chemistry Chemical Physics)

   The generation of colloidal solutions of chemically clean nanoparticles through pulsed laser ablation in liquids (PLAL) has evolved into a thriving research field that impacts industrial applications. The complexity and multiscale nature of PLAL make it difficult to untangle the various processes involved in the generation of nanoparticles and establish the dependence of nanoparticle yield and size distribution on the irradiation parameters. Large-scale atomistic simulations have yielded important insights into the fundamental mechanisms of ultrashort (femtoseconds to tens of picoseconds) PLAL and provided a plausible explanation of the origin of the experimentally observed bimodal nanoparticle size distributions. In this paper, we extend the atomistic simulations to short (hundreds of picoseconds to nanoseconds) laser pulses and focus our attention on the effect of the pulse duration on the mechanisms responsible for the generation of nanoparticles at the initial dynamic stage of laser ablation. Three distinct nanoparticle generation mechanisms operating at different stages of the ablation process and in different parts of the emerging cavitation bubble are identified in the simulations. These mechanisms are (1) the formation of a thin transient metal layer at the interface between the ablation plume and water environment followed by its decomposition into large molten nanoparticles, (2) the nucleation, growth, and rapid cooling/solidification of small nanoparticles at the very front of the emerging cavitation bubble, above the transient interfacial metal layer, and (3) the spinodal decomposition of a part of the ablation plume located below the transient interfacial layer, leading to the formation of a large population of nanoparticles growing in a high-temperature environment through inter-particle collisions and coalescence. The coexistence of the three distinct mechanisms of the nanoparticle formation at the initial stage of the ablation process can be related to the broad nanoparticle size distributions commonly observed in nanosecond PLAL experiments. The strong dependence of the nanoparticle cooling and solidification rates on the location within the low-density metal–water mixing region has important implications for the long-term evolution of the nanoparticle size distribution, as well as for the ability to quench the nanoparticle growth or dope them by adding surface-active agents or doping elements to the liquid environment. 

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2. Effect of a liquid environment on single-pulse generation of laser induced periodic surface structures and nanoparticles

   https://doi.org/10.1039/D0NR00269K  

   Shih, Cheng-Yu; Gnilitskyi, Iaroslav; Shugaev, Maxim V.; Skoulas, Evangelos; Stratakis, Emmanuel; Zhigilei, Leonid V. (April 2020, Nanoscale)

   The effect of a liquid environment on the fundamental mechanisms of surface nanostructuring and generation of nanoparticles by single pulse laser ablation is investigated in a closely integrated computational and experimental study. A large-scale molecular dynamics simulation of spatially modulated ablation of Cr in water reveals a complex picture of the dynamic interaction between the ablation plume and water. Ablation plume is found to be rapidly decelerated by the water environment, resulting the formation and prompt disintegration of a hot metal layer at the interface between the ablation and water. A major fraction of the ablation plume is laterally redistributed and redeposited back to the target, forming smooth frozen surface features. Good agreement between the shapes of the surface features predicted in the simulation and the ones generated in single pulse laser ablation experiments performed for Cr in water supports the mechanistic insights revealed in the simulation. The results of this study suggest that the presence of a liquid environment can eliminate the sharp features of the surface morphology, reduce the amount of the material removed from the target by more than an order of magnitude, and narrow down the nanoparticle size distribution as compared to laser ablation under vacuum. Moreover, the computational predictions of the effective incorporation of molecules constituting the liquid environment into the surface region of the irradiated target and the generation of high vacancy concentrations, exceeding the equilibrium levels by more than an order of magnitude, suggest a potential for hyperdoping of laser-generated surfaces by solutes present in the liquid environment. 

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3. Modulation of energy thresholds for laser-induced cavitation using gold nanoparticles

   https://doi.org/10.1117/12.3081310  

   Baker, Jacob C; Shrestha, Binita; Wang, Sicong; Rajan, Abhishek; Yadav, Aditya; Porter, Tyrone; Yang, Jin (March 2026, SPIE)

   Bixler, Joel N; Linz, Norbert; Walsh, Alex J (Ed.)

   The precise control of laser-induced cavitation (LIC) at the micro and nanoscale holds significant promise for biomedical applications ranging from targeted drug delivery and microsurgery to materials processing and microfluidics. Gold nanoparticles (AuNPs) are known to act as potent enhancers for LIC by reducing cavitation energy thresholds. However, a quantitative understanding of how AuNP properties regulate cavitation events remains limited, which is crucial for optimizing the aforementioned applications. In this study, we systematically investigate AuNP-mediated modulation of LIC energy thresholds using nanosecond laser pulses and ultra-high-speed imaging. While LIC in deionized (DI) water typically exhibits a sharp transition from no cavitation to large bubble formation (maximum bubble radius Rmax >100 μm) once a critical energy threshold is exceeded. In contrast, the introduction of AuNPs reveals four distinct cavitation regimes: (i) no observable bubbles, (ii) single small bubbles (Rmax ∼ 1-20 μm), (iii) multiple small bubbles forming bubble clouds, and (iv) single large bubbles (Rmax ∼ 100-1000 μm). Each AuNP system exhibits a characteristic energy threshold at which large cavitation emerges. We attribute these differences to a shift in the dominant cavitation nucleation mechanisms. These results demonstrate that AuNP optical properties play a critical role in governing LIC mechanisms, cavitation regimes, and energy thresholds. By enabling tunable and predictable cavitation behavior, this work provides a framework for the rational design of nanoparticle-assisted cavitation in advanced biomedical and engineering applications. 

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4. Synthesis and Unique Behaviors of High-Purity HEA Nanoparticles Using Femtosecond Laser Ablation

   https://doi.org/10.3390/nano14060554  

   Fieser, David; Lan, Yucheng; Gulino, Antonino; Compagnini, Giuseppe; Aaron, Doug; Mench, Matthew; Bridges, Denzel; Shortt, Hugh; Liaw, Peter; Hu, Anming (March 2024, Nanomaterials)

   High-entropy alloys (HEAs) are a class of metal alloys consisting of four or more molar equal or near-equal elements. HEA nanomaterials have garnered significant interest due to their wide range of applications, such as electrocatalysis, welding, and brazing. Their unique multi-principle high-entropy effect allows for the tailoring of the alloy composition to facilitate specific electrochemical reactions. This study focuses on the synthesis of high-purity HEA nanoparticles using the method of femtosecond laser ablation synthesis in liquid. The use of ultrashort energy pulses in femtosecond lasers enables uniform ablation of materials at significantly lower power levels compared to longer pulse or continuous pulse lasers. We investigate how various femtosecond laser parameters affect the morphology, phase, and other characteristics of the synthesized nanoparticles. An innovative aspect of our solution is its ability to rapidly generate multi-component nanoparticles with a high fidelity as the input multi-component target material at a significant yielding rate. Our research thus focuses on a novel synthesis of high-entropy alloying CuCoMn1.75NiFe0.25 nanoparticles. We explore the characterization and unique properties of the nanoparticles and consider their electrocatalytic applications, including high power density aluminum air batteries, as well as their efficacy in the oxygen reduction reaction (ORR). Additionally, we report a unique nanowire fabrication phenomenon achieved through nanojoining. The findings from this study shed light on the potential of femtosecond laser ablation synthesis in liquid (FLASiL) as a promising technique for producing high-purity HEA nanoparticles. 

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5. Manipulate nanoparticles with a laser-induced microbubble

   https://doi.org/10.1364/BODA.2019.JT4A.2  

   Li, Yuwen; Zhao, Chenglong (April 2019, Optical Manipulation and Its Applications 2019)

   null (Ed.)

   A laser-induced microbubble refers to a bubble that is generated in a liquid solution by CW laser illumination to light absorptive materials. In this study, we use the gold nanoparticles solutions and gold nanoparticle film as the materials to absorb the heat under illumination. Heat transfer from the gold nanoparticles to surroundings induces a sharp increase in temperature, which results the generation of the microbubbles in the solutions. Therefore, the size and position of the surface bubble can be dynamically adjusted by changing the power and position of the laser spots. Convection currents around microbubble can make the gold nanoparticles pinned to the substrate surface, which can generate the Roman ring-shape structure. And then shine the CW laser of different power on the structure, the characteristics of the structure can be changed. These effects can be used for a wide variety of applications including micro/nano-particle manipulation, active microfluidic control, as well as cell stretching and sorting. 

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