Ultrashort pulse laser ablation of dielectrics: Thresholds, mechanisms, role of breakdown

Abstract

In this paper, we establish connections between the thresholds and mechanisms of the damage and white-light generation upon femtosecond laser irradiation of wide-bandgap transparent materials. On the example of Corning Willow glass, evolution of ablation craters, their quality, and white-light emission were studied experimentally for 130-fs, 800-nm laser pulses. The experimental results indicate co-existence of several ablation mechanisms which can be separated in time. Suppression of the phase explosion mechanism of ablation was revealed at the middle of the irradiation spots. At high laser fluences, air ionization was found to strongly influence ablation rate and quality and the main mechanisms of the influence are analysed. To gain insight into the processes triggered by laser radiation in glass, numerical simulations have been performed with accounting for the balance of laser energy absorption and its distribution/redistribution in the sample, including bremsstrahlung emission from excited free-electron plasma. The simulations have shown an insignificant role of avalanche ionization at such short durations of laser pulses while pointing to high average energy of electrons up to several dozens of eV. At multi-pulse ablation regimes, improvement of crater quality was found as compared to single/few pulses.

Mid-infrared femtosecond laser-induced damages in As2S3 and As2Se3 chalcogenide glasses

“…We deduced the damage growth was caused by the “second” damage that co-existed with of other damage mechanisms rather than only electron accumulation, which is in agreement with the formation of “crater-in-crater” shape presented by Inam Mirza et al . 19 .

Figure 3Optical micrographs of multi pulses damaged As 2 S 3 ( a ) and As 2 Se 3 ( b ) at a range of laser fluences. ( c ) The diameter of damage crater observed by optical microscope as a function of laser fluence.

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Single-femtosecond-laser-pulse interaction with mica

“…Nanopores inside the bumps are still observed through the opening, hence, polymer like modification still occurs at such fluence. The increase in height of the bumps can be attributed, to the rise in lattice temperature, as evidenced by rim formation 1 . At highest fluence used in the study, i.e.…”

Laser Induced Damage Threshold of Silicon With Native and Artificial Sio2 Layer

“…Consequently, the recoil pressure exerted by the ablation products to the molten target surface may lead to formation of these rim structures [Korner 1996]. Such rim structures were also observed for large band gap dielectric materials for fluences much higher than the damage threshold of material [Mirza 2016]. Furthermore, at peak fluence above approximately 3.5 J/cm 2 (9.5 μJ) damage across the whole spot surface can be observed.…”

“…This blister formation, according to our understanding, appears to originate from the laser pulse energy absorption by the silicon surface below the SiO 2 layer. The laser energy fluence is too low for multiphoton absorption and damage of SiO 2 [Mirza 2016, Stuart 1996. Therefore, it is presumed the silicon undergoes melting and vaporization due to laser energy absorption.…”