Abstract

A fs-laser focused within a transparent glass can locally modify its material properties. Optical waveguides are directly written through refractive index changes [1], while fs-laser assisted chemical etching produces high-contrast, free-form, 3D structures [2]. The outcome depends sensitively on a combination of pulse parameters (e.g. peak field strength, energy) and cumulative effects (e.g. thermal), and would benefit from a fast closed-loop control. Since phase change/stress is expected to be reflected in the MIR absorption bands, dual-comb spectroscopy is a prime candidate, because it is inherently fast [3], phase sensitive, and broadband.

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