Great enhancement of infrared light absorption of silicon surface-structured by femtosecond laser pulses in N2 ambient

Abstract The enhanced light absorption of surface-microstructured silicon, prepared by cumulative irradiating with femtosecond laser pulses in ambient gas of N 2 , was presented in this letter. The blunt conical spikes formed on silicon surface after irradiation are of elliptic conical shape due to the linearly polarized laser irradiation. Greatly enhanced light absorption of such surface-structured silicon was observed in the whole measured wavelength range from 0.3 to 16.7 μm. The light absorptance is up to 95% over the wavelength range of 0.3∼1.1 μm and as high as 75% or more in wavelength range of 8.8∼13.3 μm, though it is down to about 30% in the wavelength range of 2∼7 μm.