Fig. 1. Time-resolved observation of laser excitation and subsequent relaxation in fused silica in (a) OTM and (b) PCM modes at energies significantly above the void-formation threshold (high-energy range). Input energy $E=43~\unicode[STIX]{x03BC}\text{J}$ and pulse duration $t_{p}=160$ fs. Two characteristic regions in terms of dynamics are indicated as LF region and HF region. (c) Estimated maximum electronic density at zero delay, at the excitation peak. (d) PCM aspect of the permanent damage. Transmission and relative phase change scale bars are given, as well as normalized (to critical density at 800 nm) scales for carrier density. The laser pulse is coming from the left.

Fig. 2. Post-irradiation PCM and photoluminescence spectroscopy analysis in the fast and slow decay zones for a typical trace in the high-energy interaction domain^[29]. (a) PCM of the modification region with the appearance of voids in the long-living excitation zone. (b) Generation of NBOHC in the soft, fast decay region, visualized by spatially mapping photoluminescence centered at 650 nm. (c) Accumulation of ODC in permanent void-like damage regions, with photoluminescence bands centered at 545 nm. A 325 nm excitation source is used.

Fig. 3. Time-resolved observation of excitation and relaxation in borosilicate BK7 in (a) OTM and (b) PCM modes at energies significantly above the void-formation threshold (high-energy range). Input energy $E=43~\unicode[STIX]{x03BC}\text{J}$ and pulse duration $t_{p}=160$ fs. Two characteristic regions in terms of dynamics are indicated as LF region and HF region. (c) Estimated peak electronic density at zero delay. (d) PCM aspect of the permanent damage. Transmission and relative phase change scale bars are given, as well as normalized (to critical density at 800 nm) scales for carrier density. The laser pulse is coming from the left.

Fig. 4. Time-resolved observation of excitation and relaxation in borosilicate BK7 and fused silica in (a) OTM and (b) PCM modes at energies moderately above the void-formation threshold. Input energy $E=4~\unicode[STIX]{x03BC}\text{J}$ and pulse duration $t_{p}=160$ fs. Two characteristic regions in terms of dynamics are visible with fast and slow carrier decay times, and specific structural arrangements accompanying the two dynamics. The differentiation in fast and slow decay times is particularly observable for a-$\text{SiO}_{2}$, with a less pregnant distinction in the case of BK7.

Fig. 5. Long delay time (ns range) PCM observation of relaxation in (a) a-$\text{SiO}_{2}$ and (b) BK7 at energies significantly above the void-formation threshold (high-energy range). Input energy $E=43~\unicode[STIX]{x03BC}\text{J}$ and pulse duration $t_{p}=160$ fs. The color bar relates to evolving relative positive and negative refractive index changes. Pressure waves traveling at the speed of sound are to be observed as moving index change regions. (c) Longer delay time (5.7 ns) PCM observations in a-$\text{SiO}_{2}$ showing a second pressure wave forming with a delay of 2.7 ns. The laser pulse is coming from the left and the source is located at the top of each image.

Fig. 6. Photo-acoustic dynamics in fused silica observable at different time delays (a) in experimental time-resolved PCM images of evolving pressure waves and (b) in photo-acoustic simulation for a moderate energy input of $4~\unicode[STIX]{x03BC}\text{J}$. Pulse duration is 2 ps for (a) and 150 fs for (b). The laser pulse is coming from the left. The color bar relates to evolving relative positive and negative refractive index changes.

Fig. 7. (a) Excitation increase (absorption maps in false colors) upon irradiation with pulses of increasing duration. (b) Pressure wave magnitude dependence in fused silica on the input pulse duration for an energy of $4~\unicode[STIX]{x03BC}\text{J}$. The color bar indicates relative positive and negative transient refractive index changes associated to thermomechanical phenomena.