Tuning the period of femtosecond laser induced surface structures in steel: From angled incidence to quill writing

Abstract

Exposure of metal surfaces to multiple ultrashort laser pulses under certain conditions leads to the formation of well-defined periodic surface structures. We show how the period of such structures in steel can be tuned over a wide range by controlling the complex interaction mechanisms triggered in the material. Amongst the different irradiation parameters that influence the properties of the induced structures, the angle of incidence of the laser beam occupies a prominent role. We present an experimental and theoretical investigation of this angle dependence in steel upon irradiation with laser pulses of 120 fs duration and 800 nm wavelength, while moving the sample at constant speed. Our findings can be grouped into two blocks. First, we observe the spatial coexistence of two different ripple periods at the steel surface, both featuring inverse scaling upon angle increase, which are related to forward and backward propagation of surface plasmon polaritons. To understand the underlying physical phenomena, we extend a recently developed model that takes into account quantitative properties of the surface roughness to the case of absorbing metals (large imaginary part of the dielectric function), and obtain an excellent match with the experimentally observed angle dependence. As second important finding, we observe a quill writing effect, also termed non-reciprocal writing, in form of a significant change of the ripple period upon reversing the sample movement direction. This remarkable phenomenon has been observed so far only inside dielectric materials and our work underlines its importance also in laser surface processing. We attribute the origin of symmetry breaking to the non-symmetric micro-and nanoscale roughness induced upon static multiple pulse irradiation, leading to non-symmetric modification of the wavevector of the coupled surface plasmon polariton.

Femtosecond Laser-Induced Periodic Surface Structures on 2D Ti-Fe Multilayer Condensates

“…The fact that mass displacement and mass removal is expected to lead to a corrugated profile means that appropriate conditions for surface plasmon excitation can be easily satisfied (for a detailed description, see Refs [ 32 , 40 , 41 , 42 ]). Thus, a periodic pattern can be produced, which is also confirmed by the experimental results [ 43 , 44 ]. This occurs irrespective of which material is on top (Fe or Ti).…”

Laser engineering of biomimetic surfaces

“…For strongly absorbing materials (metals), nearwavelength sized LSFL (type LSFL-I) are usually generated with an orientation perpendicular to the laser beam polarization. The periods are close to the laser wavelength and their specific value has been found to depend on the dielectric function of the material [203][204][205][206], the pulse number [207], and the surface roughness [205,[208][209][210]. These structures are observed in the ablative regime for fluences up to several times the ablation threshold ( Fig.…”

The Role of the Laser-Induced Oxide Layer in the Formation of Laser-Induced Periodic Surface Structures

“…Two-dimensional Fourier transform (2D-FT) analyses were performed using the free software ImageJ (version 1.52a, National Institutes of Health, Bethesda, MD, USA) to get information on the periodicity of the structures. In order to account the periodicity variation, we performed a radial average around the data cloud of interest in the Fourier space, then we fitted the data into a Gaussian distribution from which we obtained sigma (σ) as the periodicity range displayed in all the 2D-FTs [32]. AFM topographic data of specific samples were acquired in tapping mode using silicon probes with a nominal tip radius of 10 nm.…”