Double Cylindrical-Lens beam shaping enables femtosecond colloidal nanoparticle production upscale

Femtosecond laser ablation in liquids broadens nanomaterial synthesis by promoting ultrafast material transitions that can lead to metastable phases. However, it has long been limited by intrinsically low nanoparticle production rates due to the strong laser-liquid interactions leading to energy losses and beam distortion. Here, we propose a novel double cylindrical-lens beam-shaping strategy that enables precise control of the fluence distribution along the target, providing full and dynamic control of the spatial irradiation conditions. The double cylindrical-lens configuration provides dynamic control of beam ellipticity without altering the optical path, allowing the fluence to be optimally distributed over the ablation area. Gold nanoparticle production is increased up to 89 mg h⁻ 1 , a factor of 6.8 compared to conventional spherical focusing, reaching 16 mg h⁻ 1 W⁻ 1 . The experimental results are supported by beam-propagation simulations confirming the existence of an optimal fluence window for femtosecond nanoparticle production governed by the beam geometry. These findings provide a higher degree of control over ultrashort femtosecond laser ablation highlight beam shaping and the integration of 3D printed processing chambers as a decisive strategy for the next-generation of versatile and cost-effective laser-based nanomaterial production systems.