Contrary to the common belief that stronger light absorption leads to stronger photosensitivity, this paper demonstrates that ultrafast laser direct writing in silica glass with elliptical polarization yields about twice the form birefringence compared to linearly polarized light, despite having 2.5 times weaker nonlinear absorption. This is attributed to the enhanced interaction of circularly polarized light with randomly oriented bonds and hole polarons, as well as efficient tunneling ionization. Applications in multiplexed optical data storage and birefringence patterning are showcased.

Yuhao Lei, Gholamreza Shayeganrad, Huijun Wang, Masaaki Sakakura, Yanhao Yu, Lei Wang, Dmitrii Kliukin, Linards Skuja, Yuri Svirko, Peter G. Kazansky