Tailoring chiral optical properties by femtosecond laser direct writing in silica

An object that possesses chirality, that is, having its mirror image not overlayed on itself by rotation and translation, can provide a different optical response to a left- or right-handed circular polarized light. Chiral nanostructures may exhibit polarization-selective optical properties that can be controlled for micro-to-nano optical element engineering. An attractive way to induce such complex nanostructures in three-dimension in glass is femtosecond laser direct writing. However, the mechanism of femtosecond laser induced chirality remains to be unveiled due to complex physical and chemical processes occurring during the ultrashort light-matter interaction. Here, a phenomenological model is proposed and is built on two-layers phase shifters to account for this laser-induced optical chirality in an initially achiral material (silica glass). This model is based on the observation that femtosecond laser induced nanogratings own two principal contributions to its aggregate birefringent response: a form and a stress-related one. By refining this formalism, a multilayer approach is developed to imprint on demand optical rotation. Values up to +/-60?degrees at 550 nm within an optimal 80 mu m thickness in silica glass are possible, corresponding to the highest value in a glass to date. These results provide new insights of circular-optical control in micro-nano optical manufacturing and open new opportunities for photonics applications.

Automated summary

Chiral nanostructures in glass can exhibit polarization-selective optical properties, which can be controlled using femtosecond laser direct writing. A phenomenological model based on two-layers phase shifters has been proposed to explain laser-induced optical chirality in initially achiral materials. This model allows for optical rotation in silica glass with the highest value reported in glass to date, providing new opportunities for photonics applications.