Ultrafast processes on semiconductor surfaces irradiated by temporally shaped FS Laser Pulses: Tuning & Controlling surface Micro/Nano-Structures

The application of temporally shaped femtosecond laser pulses in the micro/nano-structuring of semiconductor surfaces is demonstrated. As an initial step towards full pulse shaping, sequences of double pulses with variable temporal spacing in the picosecond time domain with equal intensity have been used. Craters decorated with nm-sized ripples are formed following the laser-surface interaction depending on the irradiation conditions. The area, depth and strikingly the ripple periodicity show a dependence on the temporal delay between the double pulses. Our analysis and explanation for the dependence of the micro and nano-morphological features on the pulse delay is based on a combination of mechanisms including laser-triggered ultrafast excitation and relaxation on a semiconductor surface such as carrier excitation, ultrafast carrier-lattice energy exchanges and energy transport along with the slower phenomena of melting, the corresponding hydrodynamics and re-solidification that follow until the final surface morphology is established. Our investigations on laser-irradiated Si and ZnO surfaces are discussed. Correspondence Author – P. A. Loukakos (loukakos@iesl.forth.gr). KeywordsFS Laser Pulses; Nano-Structures.