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The design and fabrication of a integrated symmetric directional coupler dependent o the pumping power and operating at a 1534 nm wavelength is reported. The twin-core waveguide was inscribed into Er3+/Yb3+ co-doped phosphate glass by a femtosecond laser direct writing technique. By optical pumping, the coupling ratio can be modulated due to the changes induced in the refractive index of the material. The experimental results demonstrated that the coupling ratio can be tuned continuously from 100/0 to 50/50 by increasing the pump’s power from 0 to 350 mW. The developed twin-core coupler has promising applications for on-chip all-optical signal processing and communication systems.

Bragg gratings inscribed in active waveguides combine very efficient reflective properties with the amplifying capability of rare-earths, which may lead to large amplification and lasing performance. However, the response of these photonic structures highly depends on the grating parameters and working conditions, so modeling their behavior and dependences becomes fundamental. In this work, a numerical method has been implemented to simulate the optical power propagation along an Er/Yb-codoped integrated waveguide Bragg grating as a function of its most relevant operational parameters. The results obtained show the optimal conditions to maximize its performance as a highly amplifying reflector, but also its capability as a monolithic laser. In addition, the modeling results adequately match experimental values measured in fs-laser written structures in Er/Yb-codoped phosphate glass, supporting the accuracy of the numerical method developed and its usefulness for further optimizing these promising photonic structures.

The success of ultrafast laser processing strategies to fabricate reproducible nanostructures below the diffraction limit was possible in part by understanding the complex material transformation pathways triggered by laser pulses. A continuously growing scientific community has focused on the development of experimental techniques, mostly based on probing matter by light, to unravel the underlying interaction mechanisms. Often supported by theoretical modelling, these techniques have greatly contributed to today’s understanding of laser-matter interaction and enabled the identification of processing conditions that would have hardly been identified with empirical parameter scans. In this chapter, we review these light-based probing techniques, which interrogate in-situ the transient state of matter throughout its transformation from the initial state to the final state. Each technique is introduced and discussed in terms of its suitability for measuring certain transient changes induced, its spatial and temporal resolution, and is accompanied by results that illustrate its potential. Finally, a few examples of the applicability of some of these techniques in an industrial environment are given.

Femtosecond laser machining of materials has transformed into a mature high-precision technology, giving access to a wide range of applications. Yet, for a complete exploitation of its full potential, a detailed knowledge of the complex laser–matter interaction processes is required. For the case of the application-relevant material steel, a complete study of the electron dynamics and material transformation upon single laser pulse irradiation (800 nm, 120 fs) is reported. Detailed analysis of the obtained time- and fluence-dependent reflectivity map reveals that ultrafast electron heating during the pulse is directly followed by energy transfer to the lattice within a few picoseconds, reaching fluence-dependent peak temperatures from below melting threshold to above the boiling point. Moreover, an innovative approach to obtain the ultrafast-evolving 3D structure of a femtosecond laser excited material is reported, unraveling the dynamics of complex processes as melting, ablation, and solidification. Combined with modeling, the evolving optical properties, multilayer structure, and expansion velocities can be precisely determined. The information obtained from this study will contribute to further increase the achievable precision and wealth of structures that can be produced by designing efficient pulsed energy deposition schemes for selective re-excitation of the material.

In this work, NbO layers with highly improved electrical properties respect to pristine material have been produced by ultrafast-laser powder bed fusion process. The conditions required for producing uniform and compact layers of NbO from powder material have been studied and optimized. It has been established that ultrafast-laser irradiation, performed in air at room temperature, leads to the formation of dense NbO layers with the high temperature monoclinic crystal structure (H-NbO) but oxygen deficient. The layers show a preferential crystal orientation with the short axis of the monoclinic structure lying in the structure plane. This preferential orientation can be controlled by the laser irradiation conditions. Anisotropic resistivity has been observed as a consequence of the induced microstructure, while the overall material resistivity is decreased by more than eight orders of magnitude due to the oxygen deficiency. These results indicate that it is feasible to use ultrafast laser processing to promote high-temperature non-stoichiometric niobium oxide phases in a few seconds and with low energy consumption. The highly improved electrical properties of the laser irradiated NbO layers are extremely interesting for different electronic and sensing applications.

ZnO nano- and microstructures doped with K were grown by the Vapor–Solid method. Wires and needles are the main morphology observed, although some structures in the form of ribbons and triangular plates were also obtained. Besides these, ball-shaped structures which grow around a central wire were also detected. Raman and cathodoluminescence investigations suggest that variations in morphology, crystalline quality and luminescence emissions are related to the different lattice positions that K occupies depending on its concentration in the structures. When the amount is low, K ions mainly incorporate as interstitials (K), whereas K occupies substitutional positions of Zn (K) when the amount of K is increased. Electron Backscattered Diffraction shows that ribbons and triangular plates are oriented in the (0001) direction, which indicates that the growth of this type of morphologies is related to distortions introduced by the K since this position favors the growth in the (0001) plane. In the case of the ball-shaped structures, the compositional analysis and Raman spectra show that they consist of KSO. Finally, the capability of the elongated structures to act as waveguides and optical resonators was investigated. Due to the size of the K ion, practically double that of the Zn, and the different positions it can adopt within the ZnO lattice (K or K), high distortions are introduced that compromise the resonators performance. Despite this, quality factor (Q) and fineness (F) show acceptable values (80 and 10 at 544 nm, respectively), although smaller than those reported for doping with smaller size alkali, such as Li.

The fabrication of laser-induced periodic surface structures (LIPSS) over extended areas at high processing speeds requires the use of high repetition rate femtosecond lasers. It is known that industrially relevant materials such as steel experience heat accumulation when irradiated at repetition rates above some hundreds of kHz, and significant debris redeposition can take place. However, there are few studies on how the laser repetition rate influences both the debris deposition and the final LIPSS morphology. In this work, we present a study of fs laser-induced fabrication of low spatial frequency LIPSS (LSFL), with pulse repetition rates ranging from 10 kHz to 2 MHz on commercially available steel. The morphology of the laser-structured areas as well as the redeposited debris was characterized by scanning electron microscopy (SEM) and µ-Raman spectroscopy. To identify repetition rate ranges where heat accumulation is present during the irradiations, we developed a simple heat accumulation model that solves the heat equation in 1 dimension implementing a Forward differencing in Time and Central differencing in Space (FTCS) scheme. Contact angle measurements with water demonstrated the influence of heat accumulation and debris on the functional wetting behavior. The findings are directly relevant for the processing of metals using high repetition rate femtosecond lasers, enabling the identification of optimum conditions in terms of desired morphology, functionality, and throughput.

Reflectivity loss due to dust deposition over primary mirrors is a key issue for ground-based astronomical observatories. Suspended atmospheric dust falls over the optical surface affecting its performance and optical quality. Several in-situ and off-site techniques have been developed for eliminating dust particulates from optical surfaces, but all of them present important drawbacks like being time-consuming, expensive, contaminant or even involving dangerous operations in off-site approaches. Alternatively, a method based on laser-matter interaction and SENER¿s experience in ground telescopes, has been tested and developed. Laser cleaning is a discipline that covers a large range of applications, from semiconductor physical decontamination to the removal of oxides from metallic surfaces. The wide catalogue of laser systems currently available, allows us to investigate and design the best laser source for astronomical mirror maintenance. This has allowed us to develop a system that performs a proper cleaning for astronomical mirrors, which is currently bridging the gap between the laboratory demonstrator and the telescope application. In this communication we present the development of a laser cleaning system for the removal of dust particulates and contaminants attached to telescope mirror surfaces. Several configurations have been tested in the laboratory, under different conditions, and cleaning was performed over aluminized Zerodur® flat samples, that were naturally contaminated in Atacama¿s desert and Canary Islands, aiming at the definition, manufacturing, and testing of a demonstrator prototype. Results show a large improvement of reflectivity after cleaning and contribute to the design of a custom efficient laser cleaning system adapted to different observatories.

Plasmonic metasurfaces based on the extraordinary optical transmission (EOT) effect can be designed to efficiently transmit specific spectral bands from the visible to the far-infrared regimes, offering numerous applications in important technological fields such as compact multispectral imaging, biological and chemical sensing, or color displays. However, due to their subwavelength nature, EOT metasurfaces are nowadays fabricated with nano- and micro-lithographic techniques, requiring many processing steps and carrying out in expensive cleanroom environments. In this work, we propose and experimentally demonstrate a novel, single-step process for the rapid fabrication of high-performance mid- and long-wave infrared EOT metasurfaces employing ultrafast direct laser writing. Microhole arrays composing extraordinary transmission metasurfaces were fabricated over an area of 4 mm2 in timescales of units of minutes, employing single pulse ablation of 40 nm thick Au films on dielectric substrates mounted on a high-precision motorized stage. We show how by carefully characterizing the influence of only three key experimental parameters on the processed micro-morphologies (namely, laser pulse energy, scan velocity, and beam shaping slit), we can have on-demand control of the optical characteristics of the extraordinary transmission effect in terms of transmission wavelength, quality factor, and polarization sensitivity of the resonances. To illustrate this concept, a set of EOT metasurfaces having different performances and operating in different spectral regimes has been successfully designed, fabricated, and tested. Comparison between transmittance measurements and numerical simulations has revealed that all the fabricated devices behave as expected, thus demonstrating the high performance, flexibility, and reliability of the proposed fabrication method. We believe that our findings provide the pillars for mass production of EOT metasurfaces with on-demand optical propert

Microstructures of ZnO and ZrO and the corresponding composites have been grown by the Vapor-Solid method. A detailed characterization of their structural, compositional and optical properties has been performed. X-ray diffraction (XRD) and Raman spectroscopy measurements, let us identify two main phases, wurtzite ZnO and monoclinic ZrO, reinforcing the hypothesis of ZnO/ZrO composite formation. Scanning Electron Microscopy observations reveal the presence of different morphologies depending on the synthesis conditions. Chemical composition was analyzed by energy dispersive X-ray (EDX) spectroscopy. Luminescence properties were studied by photoluminescence and cathodoluminescence. Our results indicate that doping is occurring in both phases: ZnO is doped with Zr and ZrO is doped with Zn. However important differences between Zr rich and Zn rich structures are encountered. While the Zn rich structures are single phase with the characteristic wurtzite crystal structure of ZnO, the Zr rich structures are multiphase with both monoclinic and wurtzite crystal structures present, then leading to formation of the composites with interesting luminescence properties, with intense emissions in the near UV and the visble range, even at room temperature.

A new methodology to completely characterize active multicore waveguides is proposed. The method is applied to two-core waveguides written in an Er3+/Yb3+ co-doped phosphate glass by femtosecond laser inscription. Determination of the core diameter and refractive index variation is based on asymmetric excitation of the dual core waveguide and measurements of the intensity output distribution. Moreover, a single core waveguide has also been written for characterization purposes and signal enhancement measurements carried out on it have allowed the determination of the glass active properties. Finally, enhancement measurements on the two-core waveguides for different pump powers and core-to-core separations have been performed, together with simulations of the experiments using the parameters determined in the characterization procedure. The good agreement between measurements and simulations supports the validity of the characterization method presented. The proposed characterization technique is suitable for any multicore symmetric structure regardless the fabrication method and the number of cores, allowing the benefits of multi-core fibre designs to be transferred to integrated active structures.

The modification of the wetting properties of marble surfaces upon multi-scale texturing induced by ultrafast laser processing (340 fs pulse duration, 1030 nm wavelength) has been investigated with the aim of evaluating its potential for surface protection. The contact angle (CA) of a water drop placed on the surface was used to assess the wettability of the processed areas. Although the surfaces are initially hydrophilic upon laser treatment, after a few days they develop a strong hydrophobic behavior. Marble surfaces have been irradiated with different scan line separations to elucidate the relative roles of multi-scale roughness (nano- and micro-texture) and chemical changes at the surface. The time evolution of the contact angle has been then monitored up to 11 months after treatment. A short and a long-term evolution, associated to the combined effect of multi-scale roughness and the attachment of chemical species at the surface over the time, have been observed. XPS and ATR measurements are consistent with the progressive hydroxylation of the laser treated surfaces although the additional contribution of hydrocarbon adsorbates to the wettability evolution cannot be ruled-out. The robustness of the results has been tested by CA measurements after cleaning in different conditions with very positive results.

Fs-laser induced element redistribution (FLIER) has been a subject of intensive research in recent years. Its application to various types of glasses has already resulted in the production of efficient optical waveguides, tappers, amplifiers and lasers. Most of the work reported on FLIER-based waveguides refers to structures produced by the cross-migration of alkali (Na, K) and lanthanides (mostly La). The latter elements act as refractive index carrying elements. Herein, we report the production of Ba-based, FLIER-waveguides in phosphate glass with an index contrast > 10−2 . Phosphate glasses modified with the same amount of Na2O and K2O, and variable amounts of BaO and/or La2O3 were used to produce the FLIER-waveguides with Ba and or La acting as index carriers. Ba-only modified glasses show a waveguide writing threshold and light guiding performance comparable to that of La-based structures. However, mixed Ba-La glasses show a much higher element migration threshold, and much smaller compositionally modified regions. This behavior is consistent with a competition effect in the cross-migration of both elements (Ba and La) against the alkalis. Such an effect can be applied to inhibit undesired element redistribution effects in fs-laser processing applications in multicomponent glasses.

Here in, the fs-laser induced thermophoretic writing of microstructures in ad-hoc compositionally designed silicate glasses and their application as infrared optical waveguides is reported. The glass modifcation mechanism mimics the elemental thermal difusion occurring in basaltic liquids at the Earth’s mantle, but in a much shorter time scale (108 times faster) and over a well-defned micrometric volume. The precise addition of BaO, Na2O and K2O to the silicate glass enables the creation of positive refractive index contrast upon fs-laser irradiation. The infuence of the focal volume and the induced temperature gradient is thoroughly analyzed, leading to a variety of structures with refractive index contrasts as high as 2.5 × ­10–2. Two independent methods, namely near feld measurements and electronic polarizability analysis, confrm the magnitude of the refractive index on the modifed regions. Additionally, the functionality of the microstructures as waveguides is further optimized by lowering their propagation losses, enabling their implementation in a wide range of photonic devices

The replication of complex structures found in nature represents an enormous challenge even for advanced fabrication techniques, such as laser processing. For certain applications, not only the surface topography needs to be mimicked, but often also a specific function of the structure. An alternative approach to laser direct writing of complex structures is the generation of laser-induced periodic surface structures (LIPSS), which is based on directed self-organization of the material and allows fabrication of specific micro- and nanostructures over extended areas. In this work, we exploit this approach to fabricate complex biomimetic structures on the surface of steel 1.7131 formed upon irradiation with high repetition rate femtosecond laser pulses. In particular, the fabricated structures show similarities to the skin of certain reptiles and integument of insects. Different irradiation parameters are investigated to produce the desired structures, including laser repetition rate and laser fluence, paying special attention to the influence of the number of times the same area is rescanned with the laser. The latter parameter is identified to be crucial for controlling the morphology and size of specific structures. As an example for the functionality of the structures, we have chosen the surface wettability and studied its dependence on the laser processing parameters. Contact angle measurements of water drops placed on the surface reveal that a wide range of angles can be accessed by selecting the appropriate irradiation parameters, highlighting also here the prominent role of the number of scans.

The exciting properties of micro- and nano-patterned surfaces found in natural species hide a virtually endless potential of technological ideas, opening new opportunities for innovation and exploitation in materials science and engineering. Due to the diversity of biomimetic surface functionalities, inspirations from natural surfaces are interesting for a broad range of applications in engineering, including phenomena of adhesion, friction, wear, lubrication, wetting phenomena, self-cleaning, antifouling, antibacterial phenomena, thermoregulation and optics. Lasers are increasingly proving to be promising tools for the precise and controlled structuring of materials at micro- and nano-scales. When ultrashort-pulsed lasers are used, the optimal interplay between laser and material parameters enables structuring down to the nanometer scale. Besides this, a unique aspect of laser processing technology is the possibility for material modifications at multiple (hierarchical) length scales, leading to the complex biomimetic micro- and nano-scale patterns, while adding a new dimension to structure optimization. This article reviews the current state of the art of laser processing methodologies, which are being used for the fabrication of bioinspired artificial surfaces to realize extraordinary wetting, optical, mechanical, and biological-active properties for numerous applications. The innovative aspect of laser functionalized biomimetic surfaces for a wide variety of current and future applications is particularly demonstrated and discussed. The article concludes with illustrating the wealth of arising possibilities and the number of new laser micro/nano fabrication approaches for obtaining complex high-resolution features, which prescribe a future where control of structures and subsequent functionalities are beyond our current imagination.

In this work, we demonstrate the use of laser-induced periodic surface structures (LIPSS) as templates for the selective growth of ordered micro- and nanostructures of ZnO. Different types of LIPSS were first produced in Si-(100) substrates including ablative low-frequency spatial (LSF) LIPSS, amorphous-crystalline (a–c) LIPSS, and black silicon structures. These laser-structured substrates were subsequently used for depositing ZnO using the vapor–solid (VS) method in order to analyze the formation of organized ZnO structures. We used scanning electron microscopy and micro-Raman spectroscopy to assess the morphological and structural characteristics of the ZnO micro/nano-assemblies obtained and to identify the characteristics of the laser-structured substrates inducing the preferential deposition of ZnO. The formation of aligned assemblies of micro- and nanocrystals of ZnO was successfully achieved on LSF-LIPSS and a–c LIPSS. These results point toward a feasible route for generating well aligned assemblies of semiconductor micro- and nanostructures of good quality by the VS method on substrates, where the effect of lattice mismatch is reduced by laser-induced local disorder and likely by a small increase of surface roughness

Laser induced ripples that are also known as Laser Induced Periodic Surface Structures (LIPSS) have gained considerable attention by researchers and industry due to their surface functionalization applications. Surface modification with LIPSS takes place in metals, semiconductors or dielectrics [1]. Their morphology depends strongly on many parameters, both on material properties and irradiation conditions (pulse fluence, wavelength, light polarization, pulse repetition rate, and processing speed). Two types of LIPSS are distinguished by their spatial periodicity, namely high-spatial frequency LIPSS (HSFL) having a periodicity significantly smaller than the laser wavelength and low-spatial frequency LIPSS (LSFL) having a periodicity close to the laser wavelength. In this work, we have investigated the LIPSS formation on germanium by using a Ti:Sapphire (800nm, 120 fs) laser. The results show different scenarios depending on the irradiation conditions. One of these scenarios is presented in Figure 1, showing images of LIPSS formed by the same fluence but different number of pulses. For a low number of pulses, LIPSS of type HSFL were formed parallel to polarization, whereas for larger number of pulses they were of type LSFL and perpendicular to polarization. This evolution of spatial periodicity by increasing the number of pulses is fundamentally different regarding the behaviour in silicon [2], which will be discussed for comparison. On the other hand, since the spatial intensity distribution of the laser beam is Gaussian, the central disk of the irradiated spot has been exposed to the peak fluence. Suprisingly, this central disk did not present ablation but LIPSS appeared on its surroundings, as can be seen in the images. This suggests that a phase change from the crystalline phase into the amorphous one could be the origin of these LIPSS. References 1 Bonse, J., Höhm, S., Kirner, S.V., Rosenfeld, A. & Krüger, J. IEEE J. Sel. Top. Quantum Electron 2017, 23, 9000615

The formation of self-organized laser-induced periodic surface structures (LIPSS) in metals, semiconductors, and dielectrics upon pulsed laser irradiation is a well-known phenomenon, receiving increased attention because of their huge technological potential. For the case of metals, a major role in this process is played by surface plasmon polaritons (SPPs) propagating at the interface of the metal with the medium of incidence. Yet, simple and advanced models based on SPP propagation sometimes fail to explain experimental results, even of basic features such as the LIPSS period. We experimentally demonstrate, for the particular case of LIPSS on Cu, that significant deviations of the structure period from the predictions of the simple plasmonic model are observed, which are very pronounced for elevated angles of laser incidence. In order to explain this deviation, we introduce a model based on the propagation of SPPs on a rough surface that takes into account the influence of the specific roughness properties on the SPP wave vector. Good agreement of the modeling results with the experimental data is observed, which highlights the potential of this model for the general understanding of LIPSS in other metals.

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.

Unlike topography patterning, widely used for numerous applications and produced by means of different technologies, there are no simple procedures to achieve surface compositional patterning at nanometric scales. In this work we have developed a simple method for 2D patterning the composition of thin films. The method relies on the magnetron sputtering deposition at oblique angles onto patterned substrates made by laser induced periodic surface structures (LIPSS). The method feasibility has been demonstrated by depositing SiOx thin films onto LIPSS structures generated in Cr layers. A heterogeneous and aligned distribution of O/Si ratios (and different Sin+ chemical states) along the LIPSS structure in length scales of some hundreds nm's has been proven by angle resolved X-ray photoelectron spectroscopy and a patterned arrangement of composition monitored by atomic force microscopy-Raman analysis. The obtained results are explained by the predictions of a Monte Carlo simulation of this deposition process and open the way for the tailored one-step fabrication of surface devices with patterned compositions.

The ablation of a carbon target immersed in deionized water, in absence and in presence of ultrasonic waves is reported, and the differences investigated. The obtained nanostructures are characterized by transmission electron microscopy, Raman spectroscopy and photoluminescence. Transmission electron images reveal that the produced carbon nanostructures, with and without ultrasonic excitation, are graphene-like sheets with improved quality in the first case. Samples prepared with ultrasounds show graphene layers with large sizes (several microns) and regular shapes, whereas the samples prepared without ultrasounds show smaller sizes and irregular shapes; additionally, some dispersed quasi-spherical nanoparticles are observed in the samples prepared without ultrasound. Photoluminescence measurements of the obtained nanostructures reveal emission in the blue spectral region.

ZnO has been and still it is being an extensively studied material. Nevertheless, many aspects of its use for the production functional nanostructures are still open. In this work pure ZnO, ZnO:Mg and ZnO:Al nano and microstructures grown onto laser patterned polycrystalline substrates have been studied. Polycrystalline substrates were structured by ultrafast laser pulses to induce the formation of Laser Induced Periodic Surface Structures (LIPSS). The performance of the irradiated areas as growth patterns for the production of highly ordered nanostructures was then analysed. Three main types of periodic structures were induced upon fs-laser structuring depending on the irradiation conditions: LSF (Low Spatial Frequency) and HSF (High Spatial Frequency) LIPSS and pseudo-spikes (PS). It has been found that the growth of micro- and nanostructures in the irradiated regions is much faster than in the non-irradiated ones. Our results indicate that using LIPSS as growth patterns can reduce the growth time to periods much shorter than those normally used from Vapor-Solid (VS) or Vapor- Liquid-Solid) VLS growth processes. Strong differences in morphology and luminescent properties are appreciated, not only between irradiated and non-irradiated areas, but also between areas irradiated under different conditions. The best regions to be used as growth templates for VS processes are found to be those irradiated in the highest energy deposition regime, featuring pseudospikes. This widens largely the current possibilities to tailor the characteristics of the grown structures.

The increasing demand for material functionalities beyond what nature offers has boosted the search for artificially designed materials with improved performance. In the case of optics and photonics, the current challenge is to develop materials at the nanoscale that have functionalities such as emission, switching/processing and detection of light operating in a wide wavelength range ranging from the UV to the NIR. In particular, plasmonics is a promising concept to develop new technologies and applications, such as optical active devices, sensors or photovoltaic cells. Plasmonic structures with characteristic dimensions in the range of a few nanometers are based on the combination of noble metals and dielectrics, as for instance metal nanoparticles (NPs) immersed in a dielectric matrix. They present unique optical properties that are dominated by an enhanced absorption at the Surface Plasmon Resonance wavelength that depends on the size, shape and organization of NPs. This presentation will show why laser based techniques are attractive for the synthesis of plasmonic nanostructures with a tailored optical response. Alternate ns-Pulsed Laser Deposition allows different material configurations such as alloys, multilayers or nanocomposites. This versatility can be used to achieve a nanometric control over the structures as well as to produce NPs with reduced size dispersion. However, the Volmer-Weber NPs growth mode along with surface processes such as sputtering or sub-surface implantation associated to the presence of a significant fraction of energetic ions in the laser generated plasma hinder the production of NPs with well-defined symmetry axes and play a crucial role on the overall properties of the nanostructures. These shortcomings can be tackled using ns- and fs-laser postprocessing, able to change the shape and spatial distribution of NPs, as well as to produce aligned structures. This approach will be illustrated in nanostructures containing layers of Au o

Silicon can be considered as one of the pillars the electronics industry has been built on. It owes this position in part to the existence of two structurally different solid phases, having very different physical properties. Upon pulsed laser irradiation, silicon can re-solidify either in the crystalline or amorphous phase, depending on the local supercooling achieved. While this potential has been identified decades ago, it has been mostly employed in applications requiring the transformation of large areas, for instance for the fabrication of solar cells or organic light emitting diode displays. Little work has been done to imprint small phase-change structures. In this talk, we will provide an overview of our work on amorphous-crystalline micro- and nanostructures written by ultrashort laser pulses. To this end we employ two different strategies. The first one is based on a laser-induced self-organization mechanism that leads to the formation of so-called Laser Induced Periodic Surface Structures (LIPSS). LIPSS are a universal phenomenon observed in metals, semiconductors and dielectrics upon irradiation with multiple short and ultrashort laser pulses. They manifest as self-assembled sub-wavelength periodic surface structures with different symmetries that depend on the processing parameters and are typically formed via ablation. In our case, we are able to prevent ablation and fabricate periodic phase-change structures whose lateral dimensions and thickness can be controlled at will. The second strategy consists in the fabrication of surface ¿ depressed annular amorphous rings with a central crystalline disk. We show that these rings can be scaled in size and stitched together to form arrays with different symmetries, with their unit cells not being confined to circular symmetry. For both fabrication approaches we have studied the dynamics of the phase transformation using femtosecond-resolved microscopy, which enables the identification and duration of the dif

The physical origin of material removal in dielectrics upon femtosecond laser pulse irradiation (800 nm, 120 fs pulse duration) has been investigated at fluences slightly above ablation threshold. Making use of a versatile pump–probe microscopy setup, the dynamics and different key stages of the ablation process in lithium niobate have been monitored. The use of two different illumination wavelengths, 400 and 800 nm, and a rigorous image analysis combined with theoretical modelling, enables drawing a clear picture of the material excitation and expansion stages. Immediately after excitation, a dense electron plasma is generated. Few picoseconds later, direct evidence of a rarefaction wave propagating into the bulk is obtained, with an estimated speed of 3650 m/s. This process marks the onset of material expansion, which is confirmed by the appearance of transient Newton rings, which dynamically change during the expansion up to approximately 1 ns. Exploring delays up to 15 ns, a second dynamic Newton ring pattern is observed, consistent with the formation of a second ablation front propagating five times slower than the first one.