Characterization of Plasma in Microwelding of Glass Using Ultrashort Laser Pulse at High Pulse Repetition Rates

Abstract

Dynamic behavior of plasma in internal modification of glass using fs-laser pulses with high pulse repetition rates up to 1MHz is observed using high-speed video camera at 50,000 frames per second. High-speed pictures reveal striking fact that the localized plasma is produced with size much smaller than reported in literatures before, and changes its location, size, shape and brightness periodically at repetition rates of the order of kHz. The mechanism responsible for producing localized plasma and its long-term periodic motion is presented based on the analysis of free-electron density based on rate equation.

Controlling plasma distributions as driving forces for ion migration during fs laser writing

“…Moreover, the depth at which the peak of the plasma filament is located shifts towards the surface for increasing energies, consistent with a focal shift due to non-linear self-focusing [23]. It is worth noting that we found no evidence for periodic oscillations of the depth and shape of the plasma distribution as reported very recently by Miyamoto and co-workers [18]. They used a highspeed CCD camera with very short exposure times (5 s), which allowed them to record oscillations with a period of a few kHz.…”

“…By spatially overlapping the different images, a precise correlation between deposited laser energy distribution and final index distribution is obtained. A similar approach, yet without precise spatial overlap of plasma and white light transmission images, was reported very recently in the study of microwelding of borosilicate glass [18].…”

Spatial zigzag evolution of cracks in moving sapphire initiated by bursts of picosecond laser pulses for ultrafast wafer dicing

“…Similar to the spatial zigzag evolution of cracks observed in our work, the dynamic plasma motion in internal modication of glass by fs-laser pulses at a high pulse repetition rate has been reported. 66 It was explained by the evolution of freeelectron density in internal modication based on the rate equation model, which was coupled with the thermal conduction model in order to incorporate the effect of thermal ionization. 67 The model showed that highly absorbing small plasma generated near the geometrical focus moves toward the laser source periodically to cover the region, which is much larger than focus volume.…”

Ultrafast Laser Direct Writing in Glass: Thermal Accumulation Engineering and Applications

“…[21,25,26] Clarifying the principle of thermal ULDW and reviewing its current stage in the applications are highly urgent and also significant for guiding future work. [24][25][26]31,35,36] Sakakura et al revealed that the local temperature of the borosilicate glass (Corning 0211) irradiated by fs laser (pulse duration: 220 fs) would cool down to <100°C in 10 μs and suggest that the thermal accumulation becomes obvious with the pulse repetition rate greater than 100 kHz. [28] The threshold for inducing strong thermal accumulation can be identified when the local temperature is significantly higher than the matrix as the next pulse arrives.…”