Ablation and optical property modification of transparent materials with femtosecond lasers

Because of the unique laser-matter interaction processes involved, femtosecond laser micro-machining and femtosecond laser materials processing techniques are developing rapidly to stages where they may be introduced into manufacturing. Yet in both these areas, some complex interaction phenomena are not fully understood. In this talk we describe two studies of fundamental processes that impact both of these areas. These studies were made in transparent media, but their findings will be applicable to many non-transparent materials. Micro-machining in confined regions can give rise to new physical mechanisms emerging to dominate the machining process. We show this occurs in deep hole drilling of glasses by femtosecond laser pulse, where self-focusing effects takes over in the ablating process. The conditions under which this occurs will be described, and other configurations discussed where these phenomena may be important. At intensities below that required for ablation, structural modification of materials may be effected by femtosecond laser pulses. This has opened pathways towards direct femtosecond laser writing of optical waveguides, micro-fluidic systems and other structures. We will describe the controlled variation of refractive index that can be created in certain types of glasses and there potential for optical waveguides, and active optical elements. The evolution of these techniques will lead to their eventual integration for the fabrication of multi-component systems on a single chip.