TY - JOUR

T1 - LIPSS on thin metallic films

T2 - New insights from multiplicity of laser-excited electromagnetic modes and efficiency of metal oxidation

AU - Dostovalov, Alexander V.

AU - Derrien, Thibault J.Y.

AU - Lizunov, Sergey A.

AU - Přeučil, Filip

AU - Okotrub, Konstantin A.

AU - Mocek, Tomáš

AU - Korolkov, Victor P.

AU - Babin, Sergey A.

AU - Bulgakova, Nadezhda M.

N1 - Publisher Copyright: © 2019 Elsevier B.V.

PY - 2019/10/15

Y1 - 2019/10/15

N2 - Thin Cr films 28-nm thick deposited on glass substrates were processed by scanning low-intensity femtosecond laser pulses with energy well below single-pulse damage threshold. Two types of laser-induced periodic surface structures (LIPSS) were produced, depending on the scanning velocity, (1) parallel to laser light polarization with periodicity somewhat smaller than laser wavelength and (2) perpendicular to polarization with spatial period much smaller than wavelength. All structures are formed as protrusions above the initial film surface and exhibit a high degree of oxidation. To explain formation of the LIPSS and their conversion from one to another type, a rigorous numerical approach for modeling surface electromagnetic waves in thin-film geometry has been developed, which takes into account the change of optical properties of material due to laser-induced oxidation and porosity. The approach addresses the multiplicity of electromagnetic modes allowed for thin films. It has been found that the low spatial frequency LIPSS parallel to laser polarization, which are formed at low scanning velocities, are well described by the Sipe theory for surfaces of low roughness. The SEW mode responsible for high spatial frequency LIPSS formation at high scanning velocities has been identified. The mechanisms of optical feedback and transformation between types of LIPSS with scanning velocity have been proposed.

AB - Thin Cr films 28-nm thick deposited on glass substrates were processed by scanning low-intensity femtosecond laser pulses with energy well below single-pulse damage threshold. Two types of laser-induced periodic surface structures (LIPSS) were produced, depending on the scanning velocity, (1) parallel to laser light polarization with periodicity somewhat smaller than laser wavelength and (2) perpendicular to polarization with spatial period much smaller than wavelength. All structures are formed as protrusions above the initial film surface and exhibit a high degree of oxidation. To explain formation of the LIPSS and their conversion from one to another type, a rigorous numerical approach for modeling surface electromagnetic waves in thin-film geometry has been developed, which takes into account the change of optical properties of material due to laser-induced oxidation and porosity. The approach addresses the multiplicity of electromagnetic modes allowed for thin films. It has been found that the low spatial frequency LIPSS parallel to laser polarization, which are formed at low scanning velocities, are well described by the Sipe theory for surfaces of low roughness. The SEW mode responsible for high spatial frequency LIPSS formation at high scanning velocities has been identified. The mechanisms of optical feedback and transformation between types of LIPSS with scanning velocity have been proposed.

KW - Laser-induced periodic surface structures

KW - Optical feedback mechanism

KW - Oxidation

KW - Surface electromagnetic wave

KW - Thin metallic film

KW - Ultrafast laser processing

UR - http://www.scopus.com/inward/record.url?scp=85067629585&partnerID=8YFLogxK

U2 - 10.1016/j.apsusc.2019.05.171

DO - 10.1016/j.apsusc.2019.05.171

M3 - Article

AN - SCOPUS:85067629585

VL - 491

SP - 650

EP - 658

JO - Applied Surface Science

JF - Applied Surface Science

SN - 0169-4332

ER -