Investigation of high and low spatial frequency laser induced periodic surface structures on metals

This work investigates the formation of laser induced periodic surface structures (LIPSS) on the surface of two different metals, tungsten and copper. These structures were produced using 1035 nm and 517.5 nm light from a pulsed femtosecond laser. The morphology of the produced LIPSS was investigated using scanning electron microscopy, as well as fast fourier transforms (FFT) of the resulting micrographs. Evolution of the produced morphologies was explored as a function of the peak laser fluence, wavelength, polarization, and pulse count, and two distinct LIPSS were observed. Low spatial frequency LIPSS (LSFL) were observed forming at periods in the range 2λ/3≤Λ≤3λ/4 at fluences close to and exceeding the ablation threshold for each material. The observed LSFL were oriented perpendicular to the incident laser polarization and formed on both metals after irradiation by either 1035 nm or 517.5 nm light. Analysis of the inhomogeneous energy deposition determined analytically from the Sipe theory indicated these features resulted from differences in electromagnetic energy absorption across the irradiation spot. High spatial frequency LIPSS (HSFL) formed on both metals only after irradiation by 517.5 nm light at lower fluences near the damage threshold. The HSFL formed preferentially parallel to the incident polarization, with periods Λ≈162 ±8 nm on copper and Λ≈93 ±4 nm on tungsten, exhibiting a significant material dependence not observed for the LSFL. Marangoni instability driven convection could not explain the observed HSFL periods, which were instead attributed to the formation of second harmonic generated light interfering with the scattered near field. This mechanism results in LIPSS with period Λ≈λ_incident⁄2n matching the observed HSFL on both materials.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Nuclear, Plasma, Radiolgc Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Mettler, Jeremy Jacob Harry

Contributors dc:contributor

• Ruzic, David N
• Qerimi, Dren

• Laser
• Lipss
• Hsfl
• Lsfl
• Metal
• Tungsten
• Copper
• Marangoni
• Electromagnetic
• Sipe
• Femtosecond

Statement dc:rights

• Copyright 2024 Jeremy Mettler

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/127302

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F127302