Formation of periodic nanostructures induced by circularly-polarized femtosecond laser

We investigated the formation of periodic nanostructures on GaN induced by circularly-polarized femtosecond laser pulses. The structure shape changed from spiral to dots structures with increasing the pulse number. The structure change explained the previous inconsistent results, and we suggest a hypothesis for the formation dynamics. The period of the dots structures was approximately 150 nm which is almost 1/7 of the laser wavelength, and it kept crystalline comparable to the original substrate. The laser-induced periodic surface structures are expected to apply as a new fine processing technology.