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Description
Femtosecond laser ablation in liquids enables advanced control over nanoparticle (NP) structure, but efficient energy delivery remains a key challenge that can be addressed through beam-shaping strategies [1]. While conventional PLAL setups rely on spherical focusing optics, advanced spatial beam engineering offers new degrees of freedom to control energy distribution and ablation dynamics [2]. In this work, we explore a beam-shaping strategy based on an optical system composed of two cylindrical lenses, enabling independent control of the beam propagation along orthogonal transverse directions. Unlike single cylindrical lens configurations [3], the double cylindrical lens system allows tailored focal conditions and extended flexibility in defining the irradiation geometry at the target surface. Moreover, additive manufacturing by fused deposition modeling (FDM) was employed to fabricate custom-designed ablation chambers with precisely controlled liquid-layer geometries. This approach results in a controlled elliptical or quasi-line focus, increasing the effective ablation area and influencing NP generation mechanisms, shown in Figure 1a).
Experimentally, NPs were synthesised by PLAL using a Ti-Sapphire laser with 800 nm central wavelength, 35 fs and 5 kHz repetition rate. By adjusting the relative position between the two cylindrical lenses, the focal shape and fluence at the target were tuned without modifying the optical path length, enabling controlled energy deposition at the ablation plane. NP productivity was found to strongly depend on the delivered fluence, with maximum yields obtained at intermediate fluence values, indicating an optimal energy density regime. The highest productivity reached 77.1 ± 2.8 mg/h at 4.89 W, corresponding to a maximum efficiency of 15.8 ± 0.6 mg/hW, while total production of 88.9 ± 2.7 mg/h was achieved at 9.61 W, shown in Figure 1b). At lower fluence, ablation was inefficient, whereas excessive fluence promoted nonlinear effects in the liquid, reducing effective energy delivery.
Structural and optical characterization revealed spherical Au NPs with narrow size distribution (10–20 nm), depicted in Figure 1c), showing that the dual cylindrical lens configuration is an effective and flexible approach for optimizing laser ablation synthesis in liquids.
Figure 1: a) Optical setup composed of two cylindrical lenses used to generate an elliptical focus on the target surface. b) NP production rate as a function of laser fluence, which varies by adjusting D. c) Characterization of Au NPs synthesized using the dual cylindrical lens configuration.
Notes and References
[1] I. Y. Khairani, G. Mínguez-Vega, C. Doñate-Buendía, and B. Gökce, “Green nanoparticle synthesis at scale: a perspective on overcoming the limits of pulsed laser ablation in liquids for high-throughput production,” Jul. 06, 2023, Royal Society of Chemistry. doi: 10.1039/d3cp01214j.
[2] S. Molina-Prados, et al., “Beam shaping techniques for pulsed laser ablation in liquids: Unlocking tunable control of nanoparticle synthesis in liquids” Beilstein J. Nanotechnol., 2026.
[3] H. Marrapu, R. Avasarala, V. R. Soma, S. K. Balivada, and G. K. Podagatlapalli, “Silver nanoribbons achieved by picosecond ablation using cylindrical focusing and SERS-based trace detection of TNT,” RSC Adv, vol. 10, no. 67, 2020, doi: 10.1039/d0ra05942k.