nitial Cumulative Effects in Femtosecond Pulsed Laser-induced Periodic Surface Structures on Bulk Metallic Glasses
Résumé
We investigate initial cumulative irradiation effects leading to variable surface topo
graphies
and
nanoscale roughness
, and triggering eventually the formation of laser
-induce
d periodic surface
structures (LIPSS) on Zr
-based bulk metallic glasses (
Zr
41.2
Ti
13.8
Cu
12.5
Ni
10
Be
25.5
(at%)). We discuss
interconnected aspects related to electronic excitation and optical transients, potential variations in
the
cartography of thermally
-driven chemical modifications and topo
graphical
features
assisting the
surface coupling of the electromagnetic field. The transient optical properties of Zr
-based BMG
surfaces upon ultrafast irradiation
, measured by a two
-angle time
-resolved single
-pump double
-
probe ellipsometry method
, show a remarkable constancy up to the point of optical damage
and
rapid gas
-phase transition
beyond
. In
intermediate and low exposure conditions
, in t
he vicinity of
the damage domain
, mult i-
pulse
incubation
effect
s determine t
he appearance of nanoscale surface
structures. The aspects discussed here involve primarily the progression of nanoscale structuring
with
an
increasing number of fs laser pulses starting from a rough surface and evolving towards
ordered corrugation. We emp
hasize the role of initial roughness in determining light coupling and
the generation of regular stationary patterns of scattered light
, localized energy absorption
and
spatially
-variant ablation
or modulated temperature-
driven factors for surface relief
. From a material
perspective, energy dispersive X
-ray spectrometry (EDX) analysis shows potential
selective
vaporization
of light elements
, leading to gradual compositional changes and proving a spatially
-
modulated temperature pattern. A formation scenario
is proposed involving interference between the
incident laser and scattered light potentially mediated by localized surface plasmons. Finite-
difference time
-domain (FDTD) simulations are applied to validate the mechanism, showing that
LIPSS
appear
intrinsically related to
the surface superposition of electromagnetic waves
.