Fabrication of a two-dimensional periodic microflower array by three interfered femtosecond laser pulses on Al:ZnO thin films

A two-dimensional periodic microflower array was fabricated on Al:ZnO thin films by the irradiation of three interfered 800 nm femtosecond laser beams. The petals of the microflowers are ∼200 nm in size, and the intervals between the nanopetals are about 100 nm. These values are significantly smaller than the laser wavelength and its diffraction-limited scale. The evolution of microflowers with different laser fluences and irradiation times was analyzed. Theoretical analysis indicates that the interferential intensity and polarization distribution together account for the formation of microflowers with subwavelength petals. Flower periodicity with a period of microns was determined by the interferential intensity distribution, while nanopetal structures and their orientations were attributed to the interferential polarization distribution.