Broad-Band Ultra-Low-Reflectivity Multiscale Micro-Nano Structures by the Combination of Femtosecond Laser Ablation and In Situ Deposition

Localized in-situ deposition: a new dimension to control in fabricating surface micro/nano structures via ultrafast laser ablation

Controllable fabrication of surface micro/nano structures is the key to realizing surface functionalization for various applications. As a versatile approach, ultrafast laser ablation has been widely studied for surface micro/nano structuring. Increasing research efforts in this field have been devoted to gaining more control over the fabrication processes to meet the increasing need for creation of complex structures. In this paper, we focus on the in-situ deposition process following the plasma formation under ultrafast laser ablation. From an overview perspective, we firstly summarize the different roles that plasma plumes, from pulsed laser ablation of solids, play in different laser processing approaches. Then, the distinctive in-situ deposition process within surface micro/nano structuring is highlighted. Our experimental work demonstrated that the in-situ deposition during ultrafast laser surface structuring can be controlled as a localized micro-additive process to pile up secondary ordered structures, through which a unique kind of hierarchical structure with fort-like bodies sitting on top of micro cone arrays were fabricated as a showcase. The revealed laser-matter interaction mechanism can be inspiring for the development of new ultrafast laser fabrication approaches, adding a new dimension and more flexibility in controlling the fabrication of functional surface micro/nano structures.

High-performance anti-reflection micro-forests on aluminium alloy fabricated by laser induced competitive vapor deposition

Surfaces with strong anti-reflection properties have attracted the wide attention of scientists and engineers due to their great application potential in many fields. Traditional laser blackening techniques are limited by the material and surface profile, which are not able to be applied to film and large-scale surfaces. Inspired by the rainforest, a new design for anti-reflection surface structures was proposed by constructing micro-forests. To evaluate this design, we fabricated micro-forests on an Al alloy slab by laser induced competitive vapor deposition. By controlling the deposition of the laser energy, the surface can be fully covered by forest-like micro-nano structures. The porous and hierarchical micro-forests performed a minimum and average reflectance of 1.47% and 2.41%, respectively, in the range of 400-1200 nm. Different from the traditional laser blackening technique, the micro-scaled structures were formed due to the aggregation of the deposited nanoparticles instead of the laser ablation groove. Therefore, this method would lead to little surface damage and can also be applied to the aluminum film with a thickness of 50 µm. The black aluminum film can be used to produce the large-scale anti-reflection shell. Predictably, this design and the LICVD method are simple and efficient, which can broaden the application of the anti-reflection surface in many fields such as visible-light stealth, precision optical sensors, optoelectronic devices, and aerospace radiation heat transfer device.