Spatio‐temporal dynamics in nondiffractive Bessel ultrafast laser nanoscale volume structuring

Abstract

International audienceThumbnail image of graphical abstractNondiffractive ultrafast optical beams with quasi-stationary characteristics enable new regimes and scales in light-matter interactions. We discuss the action of ultrashort Bessel laser beams in bulk fused silica, emphasizing excitation dynamics with energy localization beyond diffraction limit. We shed light on relaxation channels leading to one-dimensional structures with nanoscale sections and morphologies ranging from densified matter to nanosized cavities. Space- and time-resolved absorption and phase-contrast microscopy reveals two main carrier relaxation paths. Fast exciton trapping in self-induced matrix deformations results in positive index contrast driven by swift accumulation of non-bridging oxygen hole centers and defect-driven structural rearrangements. High excitation densities determine thermomechanical paths, with onset of phase transitions and the release of pressure waves. High-aspect-ratio nanosized channels are thus created via rarefaction and liquid cavitation, accompanied by molecular decomposition and generation of oxygen deficiency. The characteristic electronic relaxation identifies the nature of structural transitions up to the onset of phase transformation. Temporal pulse dispersion regulation allows driving unique carrier dynamics with precise control over energy deposition down to the 100 nm scale. Extreme high-aspect-ratio uniform void structures can thus be fabricated in conditions of sub-micron transverse light confinemen

Excitation and relaxation dynamics in ultrafast laser irradiated optical glasses

“…This is first visible in the augmentation of the absorption level due to free carriers [ Figure 7(a)], as well as in the subsequent increase in the magnitude of the launched pressure wave [ Figure 7(b)]. A scenario discussing the role of pulse duration in defining the level and the shape of the absorption region was discussed earlier [7,23] . The pulse durations that achieved the maximal carrier density and pressure yield respectively are slightly shifted, indicating that the released pressure only partially reflects the initial energy concentration, part of the energy being spent in plastic compaction around the damage region.…”

“…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] .…”

Improved laser glass cutting by spatio-temporal control of energy deposition using bursts of femtosecond pulses

“…In contrast to high-angle Bessel beams, the laser pulse gets strongly perturbed and defocused by the nonlinear Kerr effects and induced plasma [14], that is similar to the femtosecond (fs) filamentary propagation using low NA conventional focusing optics [15]. As a consequence, a relatively low free electrons concentration and weaker material damage than expected from linear propagation dynamics is observed [16,17]. When even smaller conical angles θ B <10 • are employed, these nonlinear effects completely prevent the formation of permanent modifications [17].…”

“…When even smaller conical angles θ B <10 • are employed, these nonlinear effects completely prevent the formation of permanent modifications [17]. One way to overcome this problem is to pre-chirp the laser pulse [16,18] or use space-time focusing [19,20] and rely on temporal compression dynamics to increase the laser intensity and, thus, the energy deposition inside the medium. By using such techniques, Bessel beams were successfully employed for microstructuring of glass and semiconductors [21][22][23], drilling of microchannels in glass and silicon [18,24], as well as for cutting of thick glasses [7].…”

Front-surface fabrication of moderate aspect ratio micro-channels in fused silica by single picosecond Gaussian–Bessel laser pulse

“…Indeed, long cylindrical micro-channels with high aspect ratios [8,9] up to 1200 have been demonstrated with singleshot ultrafast pulsed Bessel beams. The previous study with Bessel beam of variable pulse duration [10] also suggested that ps pulses are more beneficial for high efficiency energy deposition and could avoid temporal dynamics effects [11,12] which can compromise the stationarity of the Bessel beam propagation. Bhuyan et al [13] demonstrated that rear-side ablation under water immersion is a good strategy to facilitate debris evacuation and for obtaining taper-free micro/nano channel fabrication.…”