Ultrafast laser processing of copper: A comparative study of experimental and simulated transient optical properties

Winter, Jan; Rapp, Stephan; Schmidt, Michael

doi:10.1016/j.apsusc.2017.02.070

Cited by 61 publications

(35 citation statements)

References 62 publications

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“…No side effects or melting was seen for longer pulses. Pulses of 10 ps length were short enough to minimise melt formation on the copper surface, which coincidence well with electron-ion thermalisation time in copper 30 . The bottom of the cavities was smooth, with no bumps or unwanted parasitic structure formation, which could ruin the aesthetic appearance of the cavities (see Fig.…”

Section: Resultssupporting

confidence: 59%

Highly-efficient laser ablation of copper by bursts of ultrashort tuneable (fs-ps) pulses

Žemaitis

Gečys

Barkauskas³

et al. 2019

Sci Rep

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Ultrashort pulse laser, capable of varying pulse duration between 210 fs and 10 ps and producing a burst of pulses with an intra-burst pulse repetition rate of 64.5 MHz (time distance between pulses 15.5 ns), was used to investigate the ablation efficiency of the copper. The study on ablation efficiency was done for various numbers of pulses per burst between 1 and 40. The increase in the ablation efficiency by 20% for 3 pulses per burst compared to a non-burst regime was observed. The comparison was made between the beam-size optimised regimes. Therefore, the real advantage of the burst regime was demonstrated. To the best of our knowledge, we report the highest laser milling ablation efficiency of copper of 4.84 µm 3 /µJ by ultrashort pulses at ~1 µm optical wavelength.

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Section: Resultssupporting

confidence: 59%

Highly-efficient laser ablation of copper by bursts of ultrashort tuneable (fs-ps) pulses

Žemaitis

Gečys

Barkauskas³

et al. 2019

Sci Rep

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“…Localization of valence electrons is expected to vary macroscopic properties of transition metals, such as conductivity, reflectivity, plasmonic behavior, magnetization and catalytic activity at surfaces. A particularly high electron density in transition metals, associated with fastest screening rates in the valence band, allows therefore to manipulate these macroscopic properties at unprecedented rates, in agreement with recent studies 37,38 . Our results unambiguously demonstrate photo-manipulation of screening in transition metals via ultrafast electron localization below the electron thermalization timescale.…”

supporting

confidence: 82%

Attosecond screening dynamics mediated by electron localization in transition metals

et al. 2019

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Transition metals with their densely confined and strongly coupled valence electrons are key constituents of many materials with unconventional properties 1 , such as high-Tc superconductors, Mott insulators and transition-metal dichalcogenides 2 . Strong electron interaction offers a fast and efficient lever to manipulate their properties with light, creating promising potential for next-generation electronics 3-6 . However, the underlying dynamics is a fast and intricate interplay of polarization and screening effects, which is poorly understood. It is hidden below the femtosecond timescale of electronic thermalization, which follows the light-induced excitation 7 . Here, we investigate the many-body electron dynamics in transition metals before thermalization sets in. We combine the sensitivity of intra-shell transitions to screening effects 8 with attosecond time resolution to uncover the interplay of photo-absorption and screening. First-principles time-dependent calculations allow us to assign our experimental observations to ultrafast electronic localization on d-orbitals. The latter modifies the whole electronic structure as well as the collective dynamic response of the system on a timescale much faster than the light-field cycle. Our results demonstrate a possibility for steering the electronic properties of solids prior to electron thermalization, suggesting that the ultimate speed of electronic phase transitions is limited only by the duration of the controlling laser pulse. Furthermore, external control of the local electronic density serves as a fine tool for testing state-of-the art models of electron-electron interactions. We anticipate our study to facilitate further investigations of electronic phase transitions, laser-metal interactions and photo-absorption in correlated electron systems on its natural timescale.A characteristic thermalization time of laser-excited hot electrons in solids is in the femtosecond regime and becomes faster with stronger electron interactions 7 . Therefore, attosecond time resolution is required to resolve coupled electron dynamics during the lasermatter interaction before electron thermalization has occurred. Attosecond transient absorption spectroscopy revealed electric-field-guided electron dynamics in simple dielectrics and semiconductors 9-14 . However, transient absorption studies of localized and strongly interacting electrons, such as on d-and f-orbitals of transition metals, have been limited to the fewfemtosecond regime 15 . Transition metal elements are the key constituents of many materials exhibiting remarkable properties, such as Mott insulators, high-Tc superconductors and transition metal dichalcogenides 2 . Understanding the coupled-electron dynamics in these systems is central for their applications in optoelectronics, energy-efficient electronics, magnetic-memory devices, spintronics and new solar cells 16 . Transition metal elements were studied with attosecond photoemission spectroscopy [17][18][19] . However, state-of-the-art theoretical

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“…In this case, the nonequilibrium electron dynamics becomes important and limits the applicability of TTM. Additionally, the pumpprobe ellipsometry measurements report the change of the absorption and refractive index of a photoexcited metal that is usually associated with the presence of thermalized electron subsystem at high temperature during the laser pulse [26,27].…”

Section: Introductionmentioning

confidence: 99%

Ultrafast electron dynamics and orbital-dependent thermalization in photoexcited metals

et al. 2018

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We use a time-dependent density functional theory (TDDFT) to analyze nonequilibrium dynamics of laserexcited electrons in transition metals (Ni, Cr, Cu) and shed light on the ultrafast thermalization process from a microscopical point of view. As a first result, after instant increase of the electron temperature up to 50 000 K, we observe that the dynamics of electron density of states is faster than a laser subcycle, on the attosecond timescale. This is related to an ultrafast rearrangement of excited electrons in space to accommodate strong changes in ion screening. Secondly, we show that the electron thermalization dynamics strongly depends on the electronic structure of a given metal. Excited by a 7-fs laser pulse, d-block transition metals exhibit two subsystems of electrons, each one achieving its own temperature. Due to a higher localization, electrons from d block stay cold, while excited delocalized sp electrons rapidly reach a high temperature. Electrons of each band of energy are mutually thermalized within the time of the laser pulse. Much more time is however needed to reach equilibrium of the whole electronic system. These results redraw the validity limits of current two-temperature models during the laser irradiation time, potentially impacting further material reaction.

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Ultrafast laser processing of copper: A comparative study of experimental and simulated transient optical properties

Cited by 61 publications

References 62 publications

Highly-efficient laser ablation of copper by bursts of ultrashort tuneable (fs-ps) pulses

Highly-efficient laser ablation of copper by bursts of ultrashort tuneable (fs-ps) pulses

Attosecond screening dynamics mediated by electron localization in transition metals

Ultrafast electron dynamics and orbital-dependent thermalization in photoexcited metals

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