Prof. Roberta Ramponi, Politecnico di Milano

Abstract:
Femtosecond laser micromachining is a powerful and flexible tool for the fabrication of both optical waveguides and, when followed by chemical etching, of microchannels, with unprecedented intrinsic 3D capabilities. Indeed, when focusing the femtosecond pulses inside transparent material, following highly nonlinear absorption, modifications are induced in the irradiated volume with different characteristics depending on the laser fluence. At lower laser fluence, “gentle” modification, resulting in refractive index change, can be exploited for direct writing of waveguides. At higher laser fluence, in suitable materials (e.g. fused silica), nanogratings are formed that result in a higher selectivity to liquid chemical etching, and thus in the realization of microchannels. This allows the direct on-chip integration of photonic functionalities and the realization of fully integrated optofluidic devices with a simple fabrication procedure that doesn’t require any previous lithographic step. The basics of the technique are discussed together with its potentials. Some examples of devices are presented, both monolithic lab-on-chips for biomedical applications and optofluidic photonic devices.