Plasma formation and relaxation dynamics in fused silica driven by femtosecond short-wavelength infrared laser pulses.

Laser-induced plasma formation and subsequent relaxation in solid dielectrics is the precursor to structural modifications that are accompanied by a permanent alteration of material properties. The decay of the electron-hole plasma through distinct relaxation channels determines the properties of the resulting modification. Based on an experimental arrangement combining a time-resolved transmission measurement with a cross-phase modulation measurement, we isolate the plasma formation and relaxation dynamics in the bulk of amorphous fused silica excited by femtosecond short-wavelength infrared ($\lambda =\,2100\,$nm) laser pulses. Whereas the relaxation time of the generated electron-hole plasma was so far assumed to be constant, our findings indicate an intensity-dependent relaxation time. We attribute this intensity dependence to vibrational detrapping of self-trapped excitons.