Laser ablation of dielectrics with pulse durations between 20 fs and 3 ps

Abstract

Laser-induced ablation has been extended down to a pulse duration of 20 fs generated by a Ti sapphire laser system at a wavelength of 780 nm. Barium aluminum borosilicate glass with an extremely high glass transformation temperature (∼600 °C) served as target material. The most significant observation was a substantial decrease of the ablation threshold fluence at pulse durations below 100 fs. All results indicate a dominant role of multiphoton absorption in addition to collisional ionization in this time domain.

Ultrashort Laser Pulses Applications

“…The breakdown takes place when the plasma originated by the avalanche electrons reaches a critical density and transfers energy to lattice ions, which expand away from the surface after the pulse has finished. In metals, the seed electrons are always present (conduction band free electrons), and in dielectrics and semiconductors they are excited from the valence to the conduction band by the pulse leading edge, either by multiphotonic ionization (Kautek et al, 1996;Perry et al, 1999) or by tunneling induced by the laser field (Keldysh, 1965;Lenzner et al, 1998). Although the seed electrons have dissimilar origins in different classes of materials, a metallization occurs in dielectrics and semiconductors after they are produced, and the avalanche evolves deterministically in time (Bass & Fradin, 1973;Du et al, 1994;Joglekar et al, 2003) in the same way in all solids, that behave like metals (Gamaly et al, 2002;Nolte et al, 1997).…”

“…When plasmas are generated in gases at low pressures, the ionized electrons can be accelerated to high energies before colliding with ions. This mechanism is known as threestep model, in which the ultrashort pulse initially ionizes an atom by either tunneling or multiphotonic absorption (Kautek et al, 1996;Keldysh, 1965;Miyazaki & Takada, 1995), then the electron is accelerated away by the oscillating electric field that brings it back to collide with the ion, emitting x-rays as its kinetic energy is converted to electromagnetic radiation (Daido, 2002). Depending on the experimental details the x-rays generated can be generated in a coherent way, originating a beam with laser characteristics.…”

Modifications in Near-Surface Layer of Transparent Dielectrics Ionized by Ultrashort Laser Pulses

“…The Coulomb interaction of ions causes their displacement and mechanical stresses inside the medium. When the Coulomb forces are too weak for causing the direct ion emission [4,5], the induced mechanical strains can be sufficiently strong to stimulate the stretched modification (the "structuring") of the near-surface layer of solid.…”

“…Intensive short laser pulses can ionize the dielectric medium, forming an array of randomly distributed ions [1][2][3][4]. The Coulomb interaction of ions causes their displacement and mechanical stresses inside the medium.…”

"Desenvolvimento de um amplificador de pulsos ultracurtos de Cr:LiSAF para um sistema laser híbrido de alta potência"

“…A ruptura ocorre quando o plasma originado pela avalanche de elétrons atinge uma densidade crítica e transfere energia para os íons da rede (quebrando suas ligações com a matriz sólida), que se expandem para longe da superfície após o pulso ter passado. Em metais os elétrons livre iniciais são os próprios elétrons da banda de condução, ao passo que em isolantes e semicondutores, os elétrons livres iniciais são criados ou por ionização multifotônica dos elétrons da banda de valência pela borda dianteira (leading edge) do pulso [158,160,161,162] , ou por tunelamento induzido pelo campo do laser [163,164] , dependendo da magnitude do campo elétrico local [165] . Após os elétrons livres iniciais estarem presentes (metalização do material) a avalanche ocorre deterministicamente [159,166,167,168] da mesma maneira em todos os sólidos (isolantes, semicondutores e metais) que passam a se comportar como se fossem metais [169,170] .…”