title: Scattering effects and high-spatial-frequency nanostructures on ultrafast laser irradiated surfaces of zirconium metallic alloys with nano-scaled topographies.
abstract: The origin of high-spatial-frequency laser-induced periodic surface structures (HSFL) driven by incident ultrafast laser fields, with their ability to achieve structure resolutions below λ/2, is often obscured by the overlap with regular ripples patterns at quasi-wavelength periodicities. We experimentally demonstrate here employing defined surface topographies that these structures are intrinsically related to surface roughness in the nano-scale domain. Using Zr-based bulk metallic glass (Zr-BMG) and its crystalline alloy (Zr-CA) counterpart formed by thermal annealing from its glassy precursor, we prepared surfaces showing either smooth appearances on thermoplastic BMG or high-density nano-protuberances from randomly distributed embedded nano-crystallites with average sizes below 200 nm on the recrystallized alloy. Upon ultrashort pulse irradiation employing linearly polarized 50 fs, 800 nm laser pulses, the surfaces show a range of nanoscale organized features. The change of topology was then followed under multiple pulse irradiation at fluences around and below the single pulse threshold. While the former material (Zr-BMG) shows a specific high quality arrangement of standard ripples around the laser wavelength, the latter (Zr-CA) demonstrates strong predisposition to form high spatial frequency rippled structures (HSFL). We discuss electromagnetic scenarios assisting their formation based on near-field interaction between particles and field-enhancement leading to structure linear growth. Finite-difference-time-domain simulations outline individual and collective effects of nanoparticles on electromagnetic energy modulation and the feedback processes in the formation of HSFL structures with correlation to regular ripples (LSFL).
authors.forename: Chen
authors.initials: C
authors.lastname: Li
authors.forename: Guanghua
authors.initials: G
authors.lastname: Cheng
authors.forename: Xxx
authors.initials: X
authors.lastname: Sedao
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang
authors.forename: Nicolas
authors.initials: N
authors.lastname: Faure
authors.forename: Damien
authors.initials: D
authors.lastname: Jamon
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Colombier
authors.forename: Razvan
authors.initials: R
authors.lastname: Stoian