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

Abstract

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, we use the aluminium 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 laser or the scanning speed of nanosecond laser. The latter combines femtosecond laser and nanosecond laser. The results show that when the process repeat number of femtosecond laser is changed from 30 to 1, the height of the induced micro-pillars on the surface of Al alloy is changed from 80µm to 6µm. As a result, the reflectivity of samples will change from ∼16% to ∼87%. The nanosecond-laser-induced micro/nano structures achieve the reflectivity changing from ∼18% to ∼79% when the scanning speed changes from 10mm/s to 400mm/s in spectrum range of 250∼2000 nm. What’s, 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 laser changes from 10mm/s to 200mm/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, we demonstrated that the two-step precise controlling strategy is applicable to variety metals such as copper, stainless steel and titanium.