broadband absorption enhancement of refractory plasmonic material with random structure

We demonstrate a broadband absorber using random structures on refractory plasmonic material. the random microstructure is fabricated by femtosecond laser on tungsten and characterized with surface roughness which described by root mean square (rms) and correlation length. results show that the absorption efficiency of random microstructure with rms of 0.8 μm and correlation length of 0.55 μm is over 90 % in the wavelength range from 200 to 1100 nm. however, the sample with surface structure rms of 0.08 μm has much lower absorption (less than 70 % for λ > 600 nm). numerical simulations agree well with the experimental results and illustrate that the structure with 0.8-μm rms and 0.55-μm correlation length has the cut-off wavelength of 2400 nm which prevents mid-infrared emission. the possibility of realizing broadband absorption by using random structures presents a flexible and efficient way for solar cell, thermophotovoltaics, and energy harvesting.