Femtosecond fiber laser based metal blackening

Abstract

In this work, blackening of metals is performed using a commercialized mode-locked femtosecond fiber laser. Different types of surface structures are produced with varying laser scanning conditions (scanning speed and pitch). The modified surface morphologies are characterized using Scan Electron Microscope (SEM) and the blackening effect was investigated both visually and through spectral measurements. Spectral measurements show that the reflectance of the processed materials decreased sharply in a wide wavelength range and varied at different rate for different scanning pitch and speed. Above 95% absorption over the entire visible wavelength range has been demonstrated for the surface structures and the absorption for specific wavelengths can go up to 98.6%. It is found that the enhanced absorption of the black metal is due to light trapping and a variety of micro- and nano-scale surface structures. This study shows the great potential applications such as constructing sensitive detectors and sensors, solar energy absorber and biomedicine. Keywords: Femtosecond laser, fiber laser, blackening, direct writing, nanostructure, light trapping.