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By adjusting the laser polarization combinations, fluences and pulse numbers, we fabricated several types of two-dimensional (2D) complex nanostructures on the surface of c -cut ZnO single crystal by the interference of three femtosecond laser beams with central wavelength of 800 nm, pulse duration of 50 fs and pulse repetition frequency of 1 kHz. The hexagonal 2D nanostructures with a period of 600 nm are very regular and uniform, in which nanoparticles, nanorings and nanoripples with sizes of 200 nm are embedded. Excited by 800 nm femtosecond laser pulses, the photoluminescence (PL) micrographs reveal that the 2D nanostructures can emit purer and brighter blue light compared with the plane surface. These nanostructures have potential applications in blue light-emitting diodes (LEDs), high density optical storage and other optoelectronic devices.

We present the formation of periodic ripples in ZnO crystal irradiated by a wavelength-tunable femtosecond laser. The results indicate that in the surface thin layer, the periods change from 0.1 lambda to lambda with laser fluences and pulse numbers, and in the subsurface layer the periods are always lambda/2n, where n is the refractive index. The formation processes and mechanisms are also discussed.

In this paper, we report the formation of long-periodic (LP) ripples with a period of 530–600 nm and short-periodic (SP) ripples with a period of 260–320 nm on stainless steel irradiated by 800 nm femtosecond laser pulses. The split of LP ripples plays the decisive role in the formation of SP ripples. We further conduct pump-probe experiments and numerical simulations to study the ultrafast dynamics of the formation of surface periodic ripples.

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.

We report the fabrication of submicrometer pits array (SP-array) on 6H-SiC surface by the interference of two femtosecond laser beams. Formation mechanisms and optical absorption of SP-array are studied. The relative reflectivity and transmissivity of white light decrease to 10% of the values of SiC crystal, and the optical absorption is enhanced to 97%. The relative reflectivity and transmissivity of incident angles within the range of 20o~60o are kept below 25%. The enhancement mechanism of optical absorption of the SP-array is also discussed.