Optical absorption of two dimensional periodic microstructures on ZnO crystal fabricated by the interference of two femtosecond laser beams.

Two dimensional (2D) periodic microstructures composed of short periodic ripples, long periodic ripples and micro-holes are fabricated on ZnO crystals via the interference of two femtosecond laser beams. The relative reflectivity and transmissivity of visible light of these 2D microstructures decrease to the values of 30% and 20%, respectively. Theoretical and experimental studies indicate that besides the effects of increased surface area, the decrease of reflectivity is influenced greatly by the Mie scattering of surface microstructures, and the transmissivity, by the damage of crystalline structures.