Real-time adaptive optimization of laser induced nano ripples by laser pulse shaping

Abstract : We propose a control technique for laser induced sub- micron ripples on titanium and silicon using femtosecond laser pulse shaping. This is based on a real-time observation method of nano ripples by diffraction of UV laser beam and programmable pulse temporal design. The feedback diffraction signal provided information of ripples' period, area, direction, and arrangement uniformity. By using a genetic algorithm optimization, ripples formation was optimized for their period tuning ability and their uniformity. The diffraction signals were validated with scanning electron microscope (SEM) images. At the generation wavelength of 800 nm and depending on the pulse form, ripples on titanium show periods from 610 nm to 680 nm, and ripples on silicon has periods from 710 - 770 nm. Laser pulse energy affects optimization due to transient energy deposit on material with pulse form effects in the threshold fluence and ripple areas.