Investigation of the wavelength dependency of the creation of sub-surface modifications in ZnS

Sub-surface femtosecond laser waveguide writing in ZnS is being investigated using both experimental and numerical simulations. We show that non-linear absorption and self-focusing play a critical role in the creation of the sub-surface modifications. The wavelength- and intensity dependence of the non-linear optical parameters change the strength of the sub-surface modifications when using lasers operating at different wavelengths. We investigate several wavelength ranges of interest, covering the wavelength peaks of the different non-linear processes. Furthermore, we compare the results of the numerical simulations to several different experiments and show a close correlation between the experimentally obtained results and the numerically obtained results. Finally, we also show that in the investigated wavelength range between 800nm and 1000nm there is no significant difference between the commonly used wavelengths for femtosecond laser processing, provided the other processing parameters are the same.