Toward the formation of crossed laser-induced periodic surface structures

Abstract

The formation of a new type of laser-induced periodic surface structures using a femtosecond pulsed laser is studied on the basis of the Sipe-Drude theory solved with a FDTD scheme. Our numerical results indicate the possibility of coexisting structures parallel and perpendicular to the polarization of the incident light for low reduced collision frequency (γ/ω 1/4, where ω is the laser frequency). Moreover, these structures have a periodicity of Λ ∼ λ in both orientations. To explain this behavior, light-matter interaction around a single surface inhomogeneity is also studied and confirms the simultaneous presence of surface plasmon polaritons and radiation remnants in orthogonal orientations at low γ/ω values.

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

“…In the latter work, the formation mechanisms of different types of LIPSS including LSFL parallel and HSFL perpendicular to the polarization were presented consistently with experimental demonstrations and for the LSFL in line with an analytical theory [19]. Based on the intrinsic optical properties of the irradiated materials, FDTD simulations allow to classify the periodic structures into specific categories [16,20,21], including type-d ("dissident") structures corresponding to LSFL being parallel to the polarization with periodicities Λ LSFL~λ /n (with n being the refractive index of material), type-s ("scattering") for LSFL perpendicular to the polarization with Λ LSFL~λ , type-m ("mixed") for a special kind of LSFL parallel to the polarization with periodicities Λ LSFL~λ , and type-r ("roughness") for HSFL structures that typically are perpendicular to the laser polarization and Λ HSFL << λ. Fuentes-Edfuf et al [8] recently published a study on the formation of LIPSS in metals where the key parameters analyzed were the beam incident angle and the role of surface roughness for the generation of surface plasmons that are ultimately responsible for the formation of LIPSS. The experiments were done in air atmosphere at room temperature using fluences above the ablation threshold.…”

“…In view of their orientation parallel to the laser beam polarization, their spatial periods of the order of λ/n, and their sub-surface presence in a transparent material, it is very likely that the physical origin of the simulated intra-film and interfacial intensity patterns carrying the LSFL ║ characteristics here lies in the type-d ("dissident") electromagnetic field structures identified earlier in FDTD simulations [16,18,20,38]. These intensity patterns are formed via the far-field interference between the electromagnetic field scattered at the rough surface and the laser beam refracted into the film and In this case, the intensity distribution was acquired at different positions only inside the oxide layer (at positive Z-positions).…”

“…A visualization of the electromagnetic fields emitted from single and multiple type-d scattering centers on dielectric surfaces predominantly in the direction perpendicular to the polarization can be found in [18,39]. Note that the type-m ("mixed") features observed in FDTD (associated with LSFL parallel to the polarization and periods close to the wavelength λ) can be ruled out here as origin of the LSFL since the necessary condition of n = Re( n) ≈ Im( n) = k [20] on the optical properties of the oxide material is not fulfilled in our case here (n = 2, k = 0 [37]). Interestingly, the spatial periods of the sub-surface LSFL patterns simulated by FDTD rather lie between λ and λ/n as it was previously reported in [21].…”

Maxwell Meets Marangoni—A Review of Theories on Laser‐Induced Periodic Surface Structures

“…[63] The FDTD calculations are able to overcome some limitations of the Sipe theory by allowing to investigate even deeper lying sub-surface regions. The work of Skolski et al [72] along with the one of Déziel et al [74] provided a classification of a variety of LIPSS as the "fingerprint" of light scattering and localized absorption, named "type-d" (dissident, manifested as LSFL-II in dielectrics and semiconductors), "type-s" (scattering, manifested as LSFL-I in semiconductors and metals), "type-m" (mixed, predicted feature), and "type-r" (roughness dependent, represented by HSFL-I) (see Table 1). Periodic supra-wavelength-sized socalled "grooves" parallel to the laser beam polarization are labeled "type-g." [63,75] Zhang et al [76] extended the FDTD approach also to metallic and plasmonically active materials and identified the contribution of the scattered near-field and far-field on the types of inhomogenous energy absorption features.…”

Constructive feedback for the growth of laser‐induced periodic surface structures

“…On metals, type-s structures are observed most of the time, but in contrast to the Sipe-Drude theory, parallel structures have also been seen on metals and this observation is currently without explanation [14,15]. Since the analytical method cannot predict the formation on metals of LIPSSs parallel to polarization, we turn to a numerical approach, the finite-difference time-domain (FDTD) method [16][17][18] to investigate further. A feedback mechanism is also included to account for the growth of LIPSSs from one laser pulse to the next [19].…”