Porous glass density tailoring by femtosecond laser pulses

In this work, a new domain of femtosecond laser-induced densification was exploited as a method for space-selective control of porous glass matrix density. The estimated refractive index change (Δn) of laser-induced modified region shows a core-cladding structure with the Δn in the range of 10−4–10−2 depending on laser pulse energy and translating speed. The approximate linear relationship between glass matrix density vs Δn is theoretically proved by employing the Lorentz–Lorenz equation. Thus, the positive and negative Δn of modified region are interpreted as the densification and rarefaction of glass matrix, respectively.