Black silicon created by interfered femtosecond laser illumination

A periodic parallel microgrooves on the silicon substrate with 2.5 um spacing covered by various nanostructures can be fabricated by using the interfered femtosecond laser illumination. The morphology created by this approach is apparently different from the common method using the femtosecond laser and sulfur hexafluoride (SF6). However, the treated silicon area could tremendously reduce the reflection from the surface. The reflectance of the structured surface is around 5% throughout the visible to near IR (1.1 um) despite of the viewing angle, which is comparative. Furthermore, the effect of the reflectance reduction is weaker but still obvious when wavelength is beyond 1.1 um, which is believed to be able to extend to the mid IR range.