Measuring thermal effects in femtosecond laser-induced breakdown of dielectrics

Abstract

International audienceA quartz sample was submitted to femtosecond laser pulses with fluences up to 6×Fc,6×Fc, where FcFc is the laser-induced breakdown fluence. A series of microthermocouples, deposited onto the surface, was used to measureheatings at the millisecond scale, at typically 50 μm from the laser impact. By using both the heat propagation equation and the Helmholtz equation to get the energy absorption profile, we estimate a minimum value of the temperature reached in the center of the crater. Even very close to Fc,Fc, this temperature is found to be ≳3000 °C,≳3000 °C, proving that heating effects play a major role in the breakdown of dielectrics

Energy transport and material removal in wide bandgap materials by a femtosecond laser pulse

“…Femtosecond laser ablation of wide bandgap materials is an active research area which has very significant scientific and engineering merits [1][2][3][4]. In the ablation process, materials are first transformed into absorbing plasma with metallic properties and, then, the subsequent laserplasma interaction causes material removals [5][6][7][8]. Energy transport in the ablation process can be divided into two stages: (1) the photon energy absorption, mainly through free electron generation and heating, and (2) the redistribution of the absorbed energy to lattice leading to material removals [8,9].…”

“…In the ablation process, materials are first transformed into absorbing plasma with metallic properties and, then, the subsequent laserplasma interaction causes material removals [5][6][7][8]. Energy transport in the ablation process can be divided into two stages: (1) the photon energy absorption, mainly through free electron generation and heating, and (2) the redistribution of the absorbed energy to lattice leading to material removals [8,9]. This stage separation is based on the assumption that free electron generation and heating are completed in such a short time that the lattice temperature remains unchanged during the duration of a femtosecond laser pulse [10].…”

Polarization-dependent elliptical crater morphologies formed on a silicon surface by single-shot femtosecond laser ablation

“…In the numerical simulation, the key issue is how to appropriately include the effects of the excited surface plasmon wave into the physical model. A smooth silicon surface ablated a crater with a diameter of 3-6 μm by fs laser in a few nanoseconds; the whole ablation process consists of two stages: (1) the photon energy absorption, mainly through free electron generation, heating, and electron excitation, on a time scale from a few femtoseconds to a few picoseconds and (2) the redistribution of the absorbed energy to the lattice, leading to material removal on a time scale from a few picoseconds to a few nanoseconds [33,34]. A small crater with a diameter around 1 μm (an even smaller crater) should be produced on a time scale of a few picoseconds during ablation process.…”

Prospect for feedback guided surgery with ultra-short pulsed laser light

“…Theoretical calculations point to a rise in temperature that decays in less than a micrometer from the site of the plasma bubble [39]. Yet direct measurements of the rise in temperature range from one-tenth to ten degrees at distances of tens to hundreds of micrometers from the site of ablation [40–42]. As a practical matter, microscopic ablations have been achieved for the cutting of fine subcellular processes [43–48], as well as the cutting of corneal tissue [49, 50] and the manipulation of fine vascular processes [51–53].…”