Femtosecond laser interaction with fused silica in surface structuring

Abstract

Precision machining of micro holes and channels on glass has attracted great interest due to its high potential for the development of integrated micro-optics and biochip device in the MEMS industries. Yet, micromachining of glass remains a great challenge due to the extreme brittleness and hardness of the material. Femtosecond laser has been considered as an advanced technique for microfabrication and micromachining of various multi-functional structures in dielectric materials through multi-photon absorption because of its high-quality and damage-free processing. However, femtosecond beam-glass interaction can be very complex when coupled with the non-linear effect of air and this is not well understood.

Using fused silica as a model optical material, the present work investigates ripple formation, microstructural evolution and the kinetics of phase transformation during femtosecond laser-glass interaction. This thesis also demonstrates the capability of using a femtosecond laser in carrying out surface micromachining of holes and gratings on fused silica. It also analyzes the effect of different laser machining parameters in terms of the machining quality, profile and chemical composition change. Furthermore, it explores the mechanism of femtosecond laser induced cracking during micromachining of fused silica, though theoretically, machining with a femtosecond laser does not induce cracking. A crack free process window is obtained for micromachining of fused silica and the micromachining process developed has potential applications in fabricating optical and microelectronic devices on transparent material.