How the Physicochemical Properties of the Bulk Material Affect the Ablation Crater Profile, Mass Balance, and Bubble Dynamics During Single‐Pulse, Nanosecond Laser Ablation in Water

Abstract

Understanding the key steps that drive the laser‐based synthesis of colloids is a prerequisite for learning how to optimize the ablation process in terms of nanoparticle output and functional design of the nanomaterials. Even though many studies focus on cavitation bubble formation using single‐pulse ablation conditions, the ablation efficiency and nanoparticle properties are typically investigated under prolonged ablation conditions with repetition rate lasers. Linking single‐pulse and multiple‐pulse ablation is difficult due to limitations induced by gas formation cross‐effects, which occur on longer timescales and depend on the target materials’ oxidation‐sensitivity. Therefore, this study investigates the ablation and cavitation bubble dynamics under nanosecond, single laser pulse conditions for six different bulk materials (Au, Ag, Cu, Fe, Ti, and Al). Also, the effective threshold fluences, ablation volumes, and penetration depths are quantified for these materials. The thermal and chemical properties of the corresponding bulk materials not only favor the formation of larger spot sizes but also lead to the highest molar ablation efficiencies for low melting materials such as aluminum. Furthermore, the concept of the cavitation bubble growth linked with the oxidation sensitivity of the ablated material is discussed. With this, evidence is provided that intensive chemical reactions occurring during the very early timescale of ablation are significantly enhanced by the bubble collapse.

Impact of Chemical and Physical Properties of Organic Solvents on the Gas and Hydrogen Formation during Laser Synthesis of Gold Nanoparticles

“…[104] This was previously reported by Kalus et al who found higher gas and hydrogen formation rates in water when using higher fluences. [105] However, correlations between gas formation and laser parameters in organic solvents have rarely been addressed so far. LAL of Au in n-hexane was performed at two different lasers and the results are shown in Table S3.…”

Time resolved studies reveal the origin of the unparalleled high efficiency of one nanosecond laser ablation in liquids

“…For ns-LAL the reflectivity change in water is more pronounced than in air due to supercritical water layer formation and an emerging vapor layer 26 . The time scale of the supercritical water layer formation is dependent on the laser fluence.…”

“…Following the observation of Starinskiy et al 26 , it is hypothesized that for pulse durations of several hundred ps to 1 ns, the laser pulse is shorter than the starting time for vapor layer formation. Thus, this loss mechanism can be excluded for 3 ps pulses.…”

“…The time scale of the supercritical water layer formation is dependent on the laser fluence. The formation starts already during the 9 ns laser beam's rising edge and fluences near the damage threshold 26 . Since, in our experiments, the threshold fluence is exceeded about 4 -5 times 15 , a very early vapor formation, i.e., reflectivity decrease, is expected.…”

“…Consequently, the laser pulses are also shielded by the forming vapor above the target surface and, later, the cavitation bubble. In a study with a 9 ns laser, the shielding at an early stage of the laser pulse was investigated after the irradiation of an Au target immersed in water 26 .…”