Nanostructuring on the surface of germanate glass by femtosecond laser direct writing

Germanate glass, owing to its high infrared transmittance, high refractive index, and excellent nonlinear optical properties, has become a key material in the field of photonics. Inducing micro-nanostructures on the surface of germanate glass using femtosecond lasers can impart new functionalities and applications to the material. In this study, self-assembled nanograting structures were successfully induced on the surface of germanate glass by femtosecond laser direct writing. The effects of laser parameters, including energy density, scanning speed, and polarization direction, on the grating morphology and periodicity were systematically investigated. We first found that curving nanogratings can be induced at a combination of high laser energy and low scanning speed. Straight nanogratings with steady periods can be obtained by reasonably increasing scanning speed. The nanograting period was found to change with varying polarization angles. By optimizing the process conditions, large-area, highly uniform nanograting arrays were successfully fabricated. Furthermore, by taking advantage of the rewritable characteristics of nanogratings, different micro-nanostructures with varying periods were produced by adjusting energy combinations in consecutive scans. These findings could extend the application of germanate glass in surface photonics and information technology.