Extended Data Fig. 3: Plasma diagnostics in a-SiO₂.

Loss of probe transmission in the irradiated region for a pump intensity of ≈12 TW/cm². The first maximum of the signal is attributed to probe depletion due to reversible two-beam coupling processes during the pump–probe overlap (symbolized as an orange region). These contributions can be safely excluded when the pump beam has propagated through the focal region, that is for τ > 200 fs. The remaining signal is then only due to absorption in the undercritical electron–hole plasma. The probe absorption decays with a characteristic time on the order of ≈150 fs, corresponding to the carrier trapping constant usually reported for fused silica³¹.