Blackening of metals using femtosecond fiber laser.

This study presents an unprecedented high throughput processing for super-blackening and superhydrophobic/hydrophilic surface on both planar and nonplanar metals surfaces. By using a high pulse repetition rate femtosecond (fs) fiber laser, a light trapping microstructure and nanostructure is generated to absorb light from UV, visible to long-wave infrared spectral region. Different types of surface structures are produced with varying laser scanning conditions (scanning speed and pitch). The modified surface morphologies are characterized using scanning electron microscope and the blackening effect is investigated through spectral measurements. Spectral measurements show that the reflectance of the processed materials decreases sharply in a wide wavelength range and the decrease occurs at different rates for different scanning pitches and speeds. Above 98% absorption over the entire visible wavelength region and above 95% absorption over the near-infrared, middle-wave infrared and long-wave infrared regions range has been demonstrated for the surface structures, and the absorption for specific wavelengths can go above 99%. Furthermore, the processing efficiency of this fs fiber laser blackening technique is 1 order of magnitude higher than that of solid-state fs laser and 4 times higher than that of picosecond (ps) laser. Further increasing of the throughput is expected by using higher repetition and higher scanning speed. This technology offers the great potential in applications such as constructing sensitive detectors and sensors, solar energy absorber, and biomedicine.