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SEM images of samples with grating of 710 nm (a), 790 nm (b) and 760 nm (c,d) irradiated with a single pulse TM polarized femtosecond laser beam, at a fluence of 1.42 J/cm 2 .
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The sensitivity of grating-coupled Surface Plasmon Polaritons (SPPs) on metallic surface has been exploited to investigate the correlation between ripples formation under ultrashort laser exposure and SPPs generation conditions. Systematic examination of coupling of single ultrashort laser pulse on gratings with appropriate periods ranging from 440...
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... TE polarized as reported on Fig. 2. The small grating depth of 10 nm avoids enhancement of ripples formation resulting from a high roughness. The irradiation of the same sample of nickel without gratings does not lead to ripples formation whatever the polarization of the laser beam, at a laser fluence of 1.42 J/cm 2 , with a single shot exposure. Fig. 3 shows the SEM images of the samples with initial periods of 710, 760 and 790 nm, irradiated with a TM polarized laser beam at a fluence of 1.42 J/cm 2 . No fine ripples perpendicular to the polarization are observed for a grating period of 710 nm nor for a grating period of 790 nm, for which we would expect a classical surface plasmon ...
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Citations
... methodologies have been employed to explore processes (i.e. such as patterning, ablation, phase transitions, etc.) by the development of appropriate experimental protocols and use of advanced theoretical multiscale models [8][9][10][11][12][13][14][15][16][17][18]. ...
... where λ is the laser wavelength, η = R [ε m ε d /(ε d + ε m )] 1/2 is the real part of the effective refractive index for metal/air (~1), R is surface reflectivity, ε d is the dielectric constant, ε m is the complex dielectric constant of a metal, and θ is the incident angle [54]. It is evident from Equation (3) that the LIPSS period is proportional to the laser irradiation wavelength and, therefore, LIPSS formed as a result of TEA CO 2 laser action should have values of 10.6 µm, which corresponds to the obtained experimental values of LIPSS periods of 9.3 and 11.0 µm. ...
This paper presents a study and comparison of surface effects induced by picosecond and nanosecond laser modification of a Ti6Al4V alloy surface under different ambient conditions: air and argon- and nitrogen-rich atmospheres. Detailed surface characterization was performed for all experimental conditions. Damage threshold fluences for picosecond and nanosecond laser irradiation in all three ambient conditions were determined. The observed surface features were a resolidified pool of molten material, craters, hydrodynamic effects and parallel periodic surface structures. Laser-induced periodic surface structures are formed by multi-mode-beam nanosecond laser action and picosecond laser action. Crown-like structures at crater rims are specific features for picosecond Nd:YAG laser action in argon-rich ambient conditions. Elemental analysis of the surfaces indicated nitride compound formation only in the nitrogen-rich ambient conditions. The constituents of the formed plasma were also investigated. Exploring the impact of process control parameters on output responses has been undertaken within the context of laser modification under different environmental conditions. Parametric optimization of the nanosecond laser modification was carried out by implementing an advanced method based on Taguchi’s parametric design and multivariate statistical techniques, and optimal settings are proposed for each atmosphere.
... Another well-known phenomenon, accompanying femtosecond irradiation of solids in damaging regimes, is the spontaneous formation of LIPSS, or laser-induced periodic surface structures [7][8][9][10][11][12][13][14][15]. Despite the long history of theoretical and experimental investigations lasting from the year 1965 [11], there is a lack of theoretical models explaining the very initial (electromagnetic) stage of spontaneous surface structuring; see reviews [7,8] for details. ...
We present the first-principle numerical study of nonlinear decay of a femtosecond laser pulse into a pair of surface plasmon polaritons (SPP) during reflection from a rough metallic surface. The ultrafast dynamics of the decay was studied at damaging laser fluences of about 1 J/cm², and the principal role of the electronic collision rate growth was proved. The resulting strongly inhomogeneous heating of metal is an important stage of laser-induced phenomena like ablation, terahertz radiation generation, and periodic surface structures formation.
... Since it was first demonstrated on semiconductor surfaces, a great amount of effort has been put into elucidating the formation mechanism of LIPSSs. 25,92 Several models concerning, e.g., scattering light field, [93][94][95][96][97] propagating surface plasmon polariton, 87,98,99 and nanoplasmonic near-field enhancement 86 have been proposed, but a clear and precise physics picture of the LIPSS formation has not yet been finalized. 25 Nevertheless, promising optoelectronics applications, such as vivid structural colors, 100-104 optical birefringence based multi-dimensional data storage, 105-107 enhanced optical absorption (e.g., "black" silicon), 100,108 and improved electrical performance, 109,110 have been enabled by LIPSSs based on different material systems. ...
Femtosecond (Fs) laser micro-/nano-fabrication technology allows direct definition of on-demand nanostructures with three-dimensional (3D) geometric features and tailored photonic functionalities in a facile manner. In addition, such a strategy is widely applicable to various material families, including dielectrics, semiconductors, and metals. Based on diverse dielectric crystals, fs-laser direct writing of optical waveguides with flexible geometries and functional waveguide-based photonic devices have been well-developed. Beyond waveguide architectures, the combination of 3D nanofabrication of fs lasers and the multi-functionalities of dielectric crystals has also lighted up the future development of novel photonic structures with features even beyond the optical diffraction limit. In this article, promising research topics on domain engineering for nonlinear optics, color centers and waveguides for integrated quantum photonics, and surface processing for integrated photonics enabled by fs laser micro-/nano-fabrication in dielectric crystals are briefly overviewed. We highlight recent progress on these research topics and stress the importance of optical aberration correction during laser fabrication, followed by a discussion of challenges and foreseeing the future development of fs laser defined nanostructures in dielectric crystals toward multi-functional photonics.
... Upon multipulse irradiation, the surface topography evolves, and the changes in its individual features and their collective interactions might affect the global optical response of the system and the periodicity of LIPSS (concept illustrated in Fig. 5.5c). There are three different aspects that have been considered here: the random distribution and concentration of individual scattering centers [24,31,49], bulk or surface roughness [21,83,84], and a grating structure itself [93,94], considering that the self-organization has already taken place. From a macroscopic point of view, surface roughness is regarded as the potential driver of the surface plasmon resonance blueshift toward smaller periods [83]. ...
... We note that the discrepancy is due to multiple factors, including limited applicability of the SPP excitation criterion for a flat interface; transient optical changes in the spatially inhomogeneous electron plasma kinetics, which are not necessarily characterized by an instantaneous Drude response with a certain electron density; contributions from evanescent surface waves; and the evolving changes of the surface topography upon irradiation with multiple pulses. In case of plasmonic metals, SPPs are likely to contribute strongly to the spatially periodic energy deposition [24,94,146]. The application of advanced models for the nonlinear optical response of laserexcited surfaces including semiconductor Maxwell-Bloch equations [56,57] or nonequilibrium approaches including the interband and intraband transitions in metals [50,51,55] can potentially provide deeper insight and resolve some of the remaining issues. ...
... The decreasing period of LSFLs with increasing number of applied pulses (tendency commonly observed for both laser-excited semiconductors [64,93,173] and metals [31,93,94,152]) was interpreted by considering inter-pulse feedback mechanisms on the evolving surface topography. For instance, according to the grating-assisted SPP theory [93], the periodicity would adapt to the changes of the surface plasmon resonance with the increasing depth of the ripple gratings. ...
Ultrashort laser pulses enable efficient energy confinement down to the nanoscale, inducing extreme thermodynamic conditions in condensed matter. In contrast to longer pulse excitation, high-energy gradients are established, able to trigger nonlinear phenomena and instabilities that result from multiphysics coupling from the atomic to the macroscale. Self-organization of matter into periodic nanoscale patterns under multipulse laser excitation is one of the most intriguing manifestations of these phenomena with a wide range of potential applications in optics and mechanics, and of a fundamental scientific interest. This chapter provides an overview of the relevant processes with a particular emphasis on material modifications occurring in dielectrics, semiconductors, or metals and a critical assessment and discussion of plausible scenarios of matter reorganization toward periodic nanoscale patterns. Relying on representative experimental observations, proposed explanations are supported by numerical simulations. The dynamic interplay between light and matter evolution is explored to pave the way for structuring self-arranged surfaces on dimensions well below the diffraction limit and reaching the sub-100-nm feature size. Open questions and unexplored directions of possible further research work are outlined along the lines of the chapter.KeywordsSelf-organizationDissipative structuresLaser-induced periodic surface structuresLaser-induced ripplesUltrafast phenomena
... For example, the effect of periodicity on the charge carrier's confinement and photon absorption [6][7][8][9][10]. Until now, the two most prevalent ideas for explaining the development of these structures have been an electromagnetic interaction (scattering and absorption) of microscopic surface roughness and stimulation of surface plasmon polaritons (SPP) and another matter reorganization based on material redistribution near the surface [11][12][13]. The main difference between the two ideas is that the spatial periodicity is initially seeded along with laser irradiation in the electromagnetic interaction model. ...
... According to the spatial period and direction, ripple structures usually include three categories, namely, nanoscale lowspatial-frequency LIPSS (LSFL) with spatial periods close to the irradiation wavelength and orientation perpendicular to the laser beam polarization, nanoscale high-spatial-frequency LIPSS (HSFL) with spatial periods less than half the wavelength and microscale groove structures with orientations parallel to the laser beam polarization. To understand the mechanisms of the formation of these ripples, several explanation models have been proposed, such as interference [24,25], surface plasma [26,27], second harmonic generation [28,29], self-organization [1,30] and Coulomb explosion [31]. However, the mechanism remains an open question, as there are still many interesting observations that cannot be clearly and fully explained. ...
... The same results were obtained by Liu B. et al. [32] and Hou S. et al. [28]. This may be caused by the non-linear effect of second harmonic generation (SHG) [26,29]. The plasma layer induced by the ultrashort laser beam cannot substantially expand in a short time, and then the interaction between this thin plasma layer and subsequent laser pulses leads to SHG. ...
The preparation of micro/nano periodic surface structures using femtosecond laser machining technology has been the academic frontier and hotspot in recent years. The formation and evolution of micro/nano periodic ripples were investigated on 2205 stainless steel machined by femtosecond laser. Using single spot irradiation with fixed laser fluences and various pulse numbers, typical ripples, including nano HSFLs (‖), nano LSFLs (⊥), nano HSFLs (⊥) and micro grooves (‖), were generated one after another in one test. The morphologies of the ripples were analyzed, and the underlying mechanisms were discussed. It was found that the nano holes/pits presented at all stages could have played a key role in the formation and evolution of micro/nano periodic ripples. A new kind of microstructure, named the pea pod-like structure here, was discovered, and it was suggested that the formation and evolution of the micro/nano periodic ripples could be well explained by the pea pod-like structure model.
... where η = R [ε m ε d /(ε d + ε m )] 1/2 is a real part of effective refractive index for metal/air, θ is incident angle, λ is laser wavelength. ε d is dielectric constant and ε m is complex dielectric constant of a metal [25]. Thus, besides the pulse number, LIPSS also depend on laser wavelength, incident angle of laser beam and material properties. ...
... The mechanism of LIPSS formation is a complex process and has been a subject of research for many years. One of the most accepted mechanisms of LIPSS formation is that these structures are formed by interference of incident laser irradiation and surface plasmons [25]. The appearance of LIPSS is expected after the interaction of low-fluence short-pulse laser irradiation (order of picoseconds and femtoseconds) with metallic surfaces under standard atmospheric conditions, as well as in the presence of gases such as nitrogen, helium, argon, etc. [63,64]. ...
In this experimental study, picosecond laser treatment was performed on a nickel-based superalloy Nimonic 263, aiming to investigate the surface effects induced by irradiation in different atmospheric conditions and, concerning changes in surface composition, regarding the possibility for improvement of its functionality. Besides the varying laser parameters, such as a number of pulses and pulse energy, environmental conditions are also varied. All surface modifications were carried out in standard laboratory conditions and a nitrogen- and argon-rich atmosphere. The resulting topography effects depend on the specific laser treatment and could be categorized as increased roughness, crater formation, and formation of the laser-induced periodic surface structures (LIPSS). Changes in the chemical surface composition are distinguished as the potential formation of the protective oxides/nitrides on the sample surface. Numerous characterization techniques analyse the resulting effects on the topography and surface parameters. The multi-response parametric optimization of the picosecond laser process was performed using an advanced statistical method based on Taguchi’s robust parameter design. Finally, the optimal parameter conditions for Nimonic 263 modification are suggested.
... It should be noted here that not only the laser polarization introduces anisotropy. Other possible influences may be the coupling to surface plasmon-polaritons [120][121][122] and local defects at the surface (e.g., scratches [77]) or in the bulk. ...
The modification of solid surfaces via the impacts of intense laser pulses and the dynamics of the relevant processes are reviewed. We start with rather weak interactions on dielectric materials, based on non-linear absorption across the bandgap and resulting in low-level local effects like electron and individual ion emission. The role of such locally induced defects in the cumulative effect of incubation, i.e., the increase in efficiency with the increasing number of laser pulses, is addressed. At higher excitation density levels, due to easier laser–material coupling and higher laser fluence, the energy dissipation is considerable, leading to lattice destabilization, surface relaxation, ablation, and surface modification (e.g., laser-induced periodic surface structures). Finally, a short list of possible applications, namely in the field of wettability, is presented.
... Notice that the excited mode is transverse magnetic field, which can explain the perpendicular orientation of the formed grating to the laser polarization. The grating period is now larger because of the effective refractive index of the surface mode, which is nearly 1. 16 At 80 mm/s, the grating disappears and replaced by a random metasurface, containing small silver particles (small white dots in the SEM image). It is interesting that, at higher speed (160 mm/s), the grating is triggered again. ...
