Flexible control over optical reflection property of metallic surfaces via pulse laser

The control of fundamental optical properties, such as transmission and reflection, over metallic surfaces plays a significant role in multiple fields like solar cells and aerospace. The direct laser etching in air can perform a variety of flexible control abilities in optical functional metal surfaces. In this paper, the authors use the aluminum alloy as an example of widely metal materials and propose two kinds of controlling strategies: large-range controlling strategy and small-range precise controlling strategy. The former changes the process repeat number of femtosecond lasers or the scanning speed of nanosecond lasers. The latter combines the femtosecond laser and the nanosecond laser. The results show that when the process repeat number of femtosecond lasers is changed from 30 to 1, the height of the induced micropillars on the surface of Al alloy is changed from 80 to 6 μm. As a result, the reflectivity of samples will change from ∼16% to ∼87%. The nanosecond laser-induced micro-/nanostructures achieve the reflectivity changing from ∼18% to ∼79% when the scanning speed changes from 10 to 400 mm/s in a spectrum range of 250–2000 nm. What is more, after being fabricated in the way of two-step controlling strategy, the reflectivity raises from ∼30% to ∼40% when the scanning speed of nanosecond lasers changes from 10 to 200 mm/s, while the reflectivity of samples fabricated simply by nanosecond laser changes from ∼18% to ∼66% when the scanning speed changes in the same range and other parameters are kept the same. In addition, the authors demonstrated that the two-step precise controlling strategy is applicable to a variety of metals such as copper, stainless steel, and titanium.