Effects of electron-phonon coupling and electron diffusion on ripples growth on ultrafast-laser-irradiated metals

Abstract

International audienceMetals exposed to ultrafast laser irradiation close to ablative regimes show often a submicron-scale (near 0.5 μm) periodic organization of the surface as ripples. Using two classes of metallic materials (transition and noble), we have determined that the ripples amplitude is strongly correlated to the material transport properties, namely electron-phonon relaxation strength, electronic diffusion, and to the energy band characteristics of the electronic laser excitation. This particularly depends on the topology of the electronic structure, including d-band effects on electronic excitation. Comparing the effects of electron-phonon nonequilibrium lifetimes for the different metals under similar irradiation conditions, we indicate how the electron-phonon coupling strength affects the electronic thermal diffusion, the speed of phase transformation and impacts on the ripples contrast. The highest contrast is observed for ruthenium, where the electron-phonon coupling is the strongest, followed by tungsten, nickel, and copper, the latter with the least visible contrast. The dependence of surface patterns contrast with fluence is linked to the dependence of the relaxation characteristics with the electronic temperature

Creation of periodic subwavelength ripples on tungsten surface by ultra-short laser pulses

“…At the same time, the ripple study has also been revived enthusiastically to further explore the laser-matter interaction physics. Until now, the ripple structures induced by femtosecond lasers have been evidenced on a variety of metals [6][7][8][9][10][11][12][13] and wide-band-gap materials [14][15][16][17][18][19][20][21].…”

Ultra-short-pulsed laser-machined nanogratings of laser-induced periodic surface structures on thin molybdenum layers

“…The fact that these LIPSS were smoother and more superficial can probably be attributed to the relatively short electron-phonon coupling time τ ep of molybdenum, when compared to the pulse duration. 6,16,17 Further study would be required to confirm this.…”

First-principles assessment of potential ultrafast laser-induced structural transition in Ni

“…Recently, a related phenomena was shown on half-filled transition metals, the photoexcitation inducing local lattice softenings with potential consequences on ultrafast solid-to-solid transition 5 . Beside this, an accurate description is necessary to correctly describe ultrafast structural dynamics 2,6 , phase transitions 7 , nanostruture formation 8 , ablation dynamics 9,10 , or strong shock propagation 11 . The interplay between ultrafast excitation and resulting excited material response still requires a comprehensive theoretical description for laser-heated materials in solid state.…”