Ultrafast double-pulse ablation of fused silica

Abstract

Ultrafast pump-probe experiments were used to study high-intensity ultrafast pulse-ablation dynamics in fused silica. Two laser pulses with varied time delay and pulse energy were used to irradiate fused silica samples and observe the transient reflectivity and transmissivity of the probe pulse. It was seen that the probe reflectivity initially increased due to the formation of free-electron plasma and then dropped to a low value within a period of about 10ps caused by a rapid structural change at the surface. The time-resolved measurements of reflectivity and transmissivity were also related to atomic force microscopy measurements of the depth of the laser-ablated hole. It was seen that the depth peaked at zero delay between the pulses and decreased within a period of about 1ps as the temporal separation between the pulses was increased caused by the screening by the plasma produced by the first pulse. When the temporal separation is about 100ps or longer, evidence for melting and resolidification during double-pulse ablation was also observed in the form of ridges at the circumference of the ablated holes.

Interaction of ultrashort-laser pulses with induced undercritical plasmas in fused silica

“…For pulses below the damage threshold the material typically shows very little plasma emission and no optical modification that can be investigated. Using double-or multipulse trains, it has been shown that a noncritical electron plasma can be produced well below the permanent damage threshold [18,19,28]. Results from simulations that access those regimes are very important to the study of this interaction and should be confirmed by experiment.…”

Femtosecond laser ablation of silver foil with single and double pulses

“…In addition, we have used double pulses with separations of up to 3.4 ns in a pump probe experiment to study a transition region between two logarithmic fluence regimes. Fairly extensive experimental results have been reported on ''single pulse'' femtosecond metal ablation, though few specifically on silver [3,7] but results on dual (or multiple) pulse ablation have been rather more limited [18][19][20][21][22][23][24][25][26][27][28][29][30][31]. By dual pulse it is always understood that the pulse separation is much less than the interpulse period (typically 1 ms) of the train of amplified femtosecond pulses used for ablation.…”

“…These can range from electron lattice relaxation times or electron diffusion times (a few ps to a few 100 ps) to times for the development of the ablation plume (up to a few 1000 ps) [26][27][28][29][30][31].…”

Excitation and relaxation dynamics in ultrafast laser irradiated optical glasses

“…dielectrics follow short-and long-living absorption phases, associated to carrier dynamics in strong or weak interaction with the glass matrix [7,[13][14][15] . The material structurally responds to this dynamics on various timescales with structural states ranging from densification (type I) to rarefaction (type II) [16][17][18][19] .…”