We exploit micro-nano structuration to achieve multifunctional windows offering outstanding optical and fluidic properties to enhance the operation of surveillance or detection devices under rainy conditions. These windows are based on synthesis of an artificial index gradient for antireflection properties and improvement of their water repellency property thanks to their structuration at a subwavelength scale with controlled conical geometries. We demonstrate the realization of multifunctional germanium windows for LWIR camera, using two approaches: nanoimprint lithography, well-known for its very high resolution enabling applications from visible to thermal infrared domain, followed by etching techniques, and 3D direct laser writing based on Two-Photon Polymerization (TPP), which is of interest thanks to its ability to manufacture complex 3D structuration directly. Optical characterization shows the ability of such windows to improve optical transmission within 8-14μm spectral range, as compared to non-structured window. In terms of water repellency, the structured windows enable an increase of the contact angle up to 160° with a very low hysteresis. To evaluate the advantage of the multifunctional windows for imaging devices, the windows are integrated in front of a thermal infrared camera and images analysis shows that the camera sensitivity is increased for the nanoimprint window thanks to the multifunctional window and high water repellency in presence of water.
Freeform and microstructured features are generated by MultiPhoton Polymerization with an ultrafast laser, on tool-steel inserts, for microreplication of optical surfaces. The generation of optical surfaces has been studied by combining laser machining and multiphoton polymerization techniques. Resolution in the range of few microns, down to 300 nm lateral dimension, has been targeted on the optically enhanced surfaces. The microstructured surfaces have been further replicated by injection molding on polymer components of several cm2. The fabrication accuracy and precision has been evaluated in terms of lateral and vertical resolution of the laser generated features, and the replicated ones. The technology aims to simplify the assembly routes for heterogeneously integrated optoelectronics through direct overmolding of the optics on the components (transceivers, LEDs or sensors), with drastic improvements in cost, productivity and performance.
Carbon nanotubes (CNTs) are one of the most promising materials for advanced electronic applications, due to its extraordinary chemical and physical properties. Non-linear interactions between photons and carbon bonds provide the possibility to fabricate unique photonic devices. In this paper we present the new technological route of single walled CNTs (SWCNTs) modification using femtosecond (fs) laser pulses to produce junctions in nanotubes through multiphoton oxidation of the carbon lattice with nanoscale resolution. SWCNTs were deposited onto Si/SiO2 substrate using gas-phase process based on thermal decomposition of ferrocene in the presence of carbon monoxide. Source and drain 100/20 nm Au/Ti electrodes were fabricated by photolithography, the gate electrode was p++ Si substrate. Samples were irradiated via fs laser with different energy fluence. Fs laser pulses at low energies were used to perform photocurrent measurements. Not modified SWCNTs and structures modified upon fs laser demonstrate a huge difference for light induced charge generation. We observed significant changes in optical and electrical properties of SWCNTs after the modification. Varying the parameters of power and laser scanning speed we can change the level of local oxidation of SWCNT and photocurrent in produced photodetectors.
The development of planar functional junction provides continuous, single-atom thick, in-plane integrated circuits. The production of atomic contacts of different materials (hetero/homostructures) is still a challenging task for 2D materials technology. In this paper we describe a new method of formation of a photosensitive junction by femtosecond laser pulses patterning of graphene FET. The laser-induced oxidation of graphene goes under high intensity laser pulses, which provide nonlinear effects in graphene like multiphoton absorption and hot carrier generation. The process of laser induced local oxidation is studied on single-layer graphene FET produced by wet transfer of CVD grown graphene on copper foil onto a Si/SiO2 substrate. The 280 fs laser with 515 nm wavelength with various pulse energies is applied to modify of local electrical and optical properties of graphene. Thus, the developed process provides mask-less laser induced in-plane junction patterning in graphene. The scale of local heterojunction fabrication is about 1 μm. We observe that with an increasing of the laser fluence the number of defects increases according to two different mechanism for low and high fluences, respectively. The change of the charge carrier concentration causes the Dirac point shift in produced structures. We investigate the photoresponse in graphene junctions under fs pulsed laser irradiation with subthreshold energies. The response time is rather high while relaxation time is large because of charge traps at the graphene/SiO2 interface.
This paper describes the recent results in ultrafast (femtoseconds and picoseconds) pulsed laser patterning of graphene films (single layer graphene, graphene oxide (GO)). We investigated such effects of nonlinear optical interaction like selective laser ablation of graphene, laser reduction of graphene oxide and local functionalization (oxidation) of graphene based on multiphoton absorption for microelectrode patterning. The graphene oxide and reduction was demonstrated under femtosecond laser pulses as well as fine ablation for monolayer GO films under ps laser pulses. We demonstrated the patterned laser reduction over the GO film leads to minimum in resistance for laser fluence because of interplay of chemical and thermal effects in carbon lattice and photons. The micro-scale patterns in graphene on SiO2 substrates were fabricated using ultrashort 515 nm laser pulses. For both picosecond and femtosecond laser pulses two competitive processes, based on photo-thermal (ablation) and photochemical (oxidation/etching) effects, were observed. The laser-induced etching of graphene starts just below the threshold energy of graphene ablation. The mechanisms of ultrafast laser interaction with graphene are discussed. Patterned graphene was investigated by AFM, microRaman, SEM and sheet resistance measurements and other techniques. The mechanisms of ultrafast laser interaction with graphene are discussed. The comprehensive models of graphene oxidation/reduction are suggested.
We have developed the ultra-short pulsed laser processing methods for patterning of graphene field effect transistors in topological and chemical way. We investigated in details the photoresponse in graphene FETs before and after laser-induced modification for laser influence below threshold energy. We observed two different mechanisms of the photoresponse under ultra-short laser pulses (280 fs). The photocurrent, observed for both pristine and laser processed graphene is raised because the laser induced charge is transferred from graphene to trapped levels in SiO2 surface resulting in electrostatic Dirac point shift. For laser oxidized areas we observed more pronounced photocurrent because of heterojunction formation in laser-processed area. While for electrostatic effect the relaxation time estimated as 50 seconds, the heterojunction relaxation was observed for less than 3 ms.
Carbon nanomaterials is among the most promising technologies for advanced electronic applications, due to their extraordinary chemical and physical properties. Nonetheless, after more than two decades of intensive research, the application of carbon-based nanostructures in real electronic and optoelectronic devices is still a big challenge due to lack of scalable integration in microelectronic manufacturing. Laser processing is an attractive tool for graphene device manufacturing, providing a large variety of processes through direct and indirect interaction of laser beams with graphene lattice: functionalization, oxidation, reduction, etching and ablation, growth, etc. with resolution down to the nanoscale. Focused laser radiation allows freeform processing, enabling fully mask-less fabrication of devices from graphene and carbon nanotube films. This concept is attractive to reduce costs, improve flexibility, and reduce alignment operations, by producing fully functional devices in single direct-write operations. In this paper, a picosecond laser with a wavelength of 515 nm and pulse width of 30 ps is used to pattern carbon nanostructures in two ways: ablation and chemical functionalization. The light absorption leads to thermal ablation of graphene and carbon nanotube film under the fluence 60-90 J/cm2 with scanning speed up to 2 m/s. Just under the ablation energy, the two-photon absorption leads to add functional groups to the carbon lattice which change the optical properties of graphene. This paper shows the results of controlled modification of geometrical configuration and the physical and chemical properties of carbon based nanostructures, by laser direct writing.
We present a novel approach for real-time defect detection and classification in laser welding processes based on the use of uncooled PbSe image sensors working in the MWIR range. The spatial evolution of the melt pool was recorded and analyzed during several welding procedures. A machine learning approach was developed to classify welding defects. Principal components analysis (PCA) is used for dimensionality reduction of the melt pool data. This enhances classification results and enables on-line classification rates close to 1 kHz with non-optimized code prototyped in Python. These results point to the feasibility of real-time defect detection.
Rodrigo Linares, German Vergara, Raúl Gutiérrez, Carlos Fernández, Víctor Villamayor, Luis Gómez, Maria González-Camino, Arturo Baldasano, G. Castro, R. Arias, Y. Lapido, J. Rodríguez, Pablo Romero
The combination of flexibility, productivity, precision and zero-defect manufacturing in future laser-based equipment are a major challenge that faces this enabling technology. New sensors for online monitoring and real-time control of laserbased processes are necessary for improving products quality and increasing manufacture yields. New approaches to fully automate processes towards zero-defect manufacturing demand smarter heads where lasers, optics, actuators, sensors and electronics will be integrated in a unique compact and affordable device.
Many defects arising in laser-based manufacturing processes come from instabilities in the dynamics of the laser process. Temperature and heat dynamics are key parameters to be monitored. Low cost infrared imagers with high-speed of response will constitute the next generation of sensors to be implemented in future monitoring and control systems for laser-based processes, capable to provide simultaneous information about heat dynamics and spatial distribution.
This work describes the result of using an innovative low-cost high-speed infrared imager based on the first quantum infrared imager monolithically integrated with Si-CMOS ROIC of the market. The sensor is able to provide low resolution images at frame rates up to 10 KHz in uncooled operation at the same cost as traditional infrared spot detectors. In order to demonstrate the capabilities of the new sensor technology, a low-cost camera was assembled on a standard production laser welding head, allowing to register melting pool images at frame rates of 10 kHz. In addition, a specific software was developed for defect detection and classification. Multiple laser welding processes were recorded with the aim to study the performance of the system and its application to the real-time monitoring of laser welding processes. During the experiments, different types of defects were produced and monitored. The classifier was fed with the experimental images obtained. Self-learning strategies were implemented with very promising results, demonstrating the feasibility of using low-cost high-speed infrared imagers in advancing towards a real-time / in-line zero-defect production systems.
This work explores the combination of laser transfer and laser doping in a single process, as a way to produce highly defined, heavily doped volumes on semiconductors, to produce electronic devices. The process has been realized on mono and multicrystalline silicon by means of nanosecond laser pulses. The paper studies the mechanism of the process and the requirements in terms of beam shaping, energy levels and specific constrains of the setup to get proper dopant transfer and diffusion, as well as high compositional gradient. Bismuth is selected as n-dopant, and aluminum is used as an already well known solution for laser driven heavy p-doping on silicon. The suitability of laser transfer doping for direct writing of electronic devices is assessed in terms of transfer, melting and doping capability, and compared with other State-of-the-Art laser doping processes.
Surface texturing of metallic surfaces is studied in mixed regimes of ablation and melting, by adjusting time and energy
distribution of infrared lasers, for textures combining ablated and elevated topography in relation to the original surface.
This can allow for higher productivities and a wider range of geometries than purely ablative micromachining LST.
A methodology is presented for producing regular patterns of micron sized features on metals. By adjusting scanning
patterns, features well under the beam size can be obtained, resulting from the displacement of the molten bath by the
intense recoil pressure generated by the ablated metal. By engineering the flow of the bath and the position of the recast
material, very high aspect ratio structures can be obtained, with limits very dependent on the characteristics (viscosity,
temperature, ...) of the molten bath. 2-5 microns sized walls, 40 microns high, were obtained with nanosecond laser of
50 microns beam diameter on titanium. Sub-nanosecond laser pulses were also studied: passively q-switched lasers with
400-500 ps pulse length provide very precise control of molten pool displacement and fine feature generation.
Ni-Cr and Ni-Cu coated steel was textured in the form of two dimensional square textures and ribletted surfaces, in order
to evaluate the molten metal flow, the progressive shaping of the textures and the redistribution of the layer components
during the process.
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