Wavelength-Independent Performance of Femtosecond Laser Dielectric Ablation Spanning Over Three Octaves

Ultrafast laser breakdown of wide-band-gap dielectrics is today a key for major technologies ranging from three-dimensional material processing in optical materials to nanosurgery. However, a contradiction persists between the strongly nonlinear character of energy absorption and the robustness of processes to the changes of the band gap:wavelength ratio depending on applications. While various materials and band gaps have been studied, we concentrate here on the investigations of the spectral domain with experiments performed with wavelength drivers varied from deep ultraviolet (258 nm) to midinfrared (3.5 mu m). The measured fluence thresholds for single-shot ablation in dielectrics using 200-fs pulses exhibit a plateau extending from the visible domain up to 3.5-mu m wavelength. This is accompanied, after ablation crater analysis, by a remarkable invariance of the observed ablation precision and efficiency. Only at the short-est tested wavelength of 258 nm, a twofold decrease of the ablation threshold and significant changes of the machining depths are detected. This defines a lower spectral limit of the wavelength-independence of the ablation process. By comparison with simulations, avalanche ionization coefficients are extracted and compared with those predicted with the Drude model. This must be beneficial to improve predictive mod-els and process engineering developments exploiting the emerging high-power ultrafast laser technologies emitting in various spectral domains.