Ludovic Rapp

We report on the fabrication and femtosecond-laser-damage characterization of ion-beam-sputtered TiO ₂ /SiO ₂ multilayer mirror coatings designed for operation at 1030 nm under high-repetition-rate irradiation. The 41-layer dielectric stack deposited on fused silica substrates demonstrates a non-damaging fluence threshold of 0.80J/cm ² under 275 fs pulse irradiation at 1 MHz repetition rate. No measurable optical degradation or structural modification was observed following exposure exceeding 10 ⁹ laser pulses at sub-threshold fluence. Damage probability exhibits a sharp transition between 0.80 and 1.00J/cm ² , with catastrophic optical damage occurring at 1.00J/cm ² . The coatings maintain transmission below 0.008% throughout testing, indicative of minimal absorption and high reflectivity stability. Despite the lower intrinsic bandgap of TiO ₂ compared to conventionally preferred high-index oxides, the demonstrated performance approaches that of high-bandgap multilayer systems, indicating that optimized multilayer engineering and defect suppression can compensate for intrinsic material limitations. These results establish TiO ₂ /SiO ₂ multilayer coatings as viable candidates for high-power, MHz-regime femtosecond laser systems requiring both high damage resistance and long-term operational stability.

L’utilisation de composés organiques comme matériaux actifs représente la prochaine génération technologique. Ils permettent notamment un procédé de fabrication moins cher,de grands rendements de production ainsi que la capacité d’employer des supports souples.Ce travail présente le développement d’une technique de transfert reposant sur l’ablation laser pour le dépôt fonctionnel de films minces localisé de matériaux organiques et inorganiques en phase liquide ou solide dans le but de fabriquer des transistors à films minces organiques (OTFT).La technique de dépôt est basée sur le LIFT (laser-induced forward transfer), dont le principe de fonctionnement implique que le matériau à transférer soit préalablement préparé sur un substrat transparent. Le matériau est irradié à travers ce dernier par une impulsion laser, déclenchant l’ablation et l’éjection de la matière du substrat. Le matériau éjecté est alors recueilli sur un substrat récepteur placé devant le film donneur. Par cette méthode, des structures précisément définies par la forme du faisceau laser peuvent être transférées.L’irradiation directe de la matière à transférer n’est pas admissible pour les composés sensibles, par conséquent, une modification de la technique a été introduite pour résoudre cette limitation. Cette modification implique l’utilisation d’une couche sacrificielle, qui est spécialement adaptée pour l’ablation laser dans l’ultraviolet. Cette couche sacrificielle est déposée entre le substrat et le matériel à transférer, son but est d’absorber l’impulsion laser, de se décomposer et de propulser le matériau sur le substrat receveur tout en le protégeant de l’irradiation laser. Des matériaux métalliques et un matériau organique, le polymère triazene, ont été étudiés.Le processus de transfert a été étudié par ombroscopie résolue en temps. L’analyse de la trajectoire du matériel éjecté ainsi que de l’onde de choc créée par l’ablation a été effectuée. Ces mesures nous ont permis de déterminer les conditions de transfert optimales pour chacun des matériaux étudiés et ont montré que la condition la plus favorable pour un transfert réussi est le proche contact dans le cas des matériaux en phase solide et quelques centaines de micromètres pour les matériaux en phase liquide.Enfin, la fabrication de transistors organiques opérationnels dans différentes configurations(bottom et top gate en configuration bottom et top contact) est démontrée. Les structures imprimées prouvent la capacité de la technique LIFT à transférer différents types de matériaux en maintenant leurs propriétés à un niveau significatif de performance. Le transfert d’un ensemble multicouche OTFT est étudié. Les pixels transférés sont entièrement fonctionnels et présentent des propriétés compétitives à des dispositifs préparés par des techniques classiques

Recent research and development into the formation of nanoscale channels as a central component of nanofluidic biochip systems revolutionized the biological and chemical fields. Exploration of new pathways to form nanochannels is increasingly necessary to provide a new generation of analytical tools with accurate control of liquid fluid flow, high selectivity and increased mass flow rate. Here, we demonstrate that a single 9-keV pulse from X-ray free-electron-laser can form a nanoscale mm-long cavity in LiF. The laser-generated shock pressure results in channel formation with >1,000 length-to-diameter aspect ratio. The development of void is analyzed via continuum and atomistic simulations revealing a sequence of processes leading to the final long cavity structure. This work presents the study of mm-long nanochannel formation by a single high-brilliance X-ray free-electron laser pulse. With MHz repetition rate X-ray free electron laser opens a new avenue for the development of lab-on-chip applications in any material, including those non-transparent to optical lasers.

This study investigates the possibility of using a femtosecond pulse laser to remove iron ore slurry used to stabilise blast-hole structures by mining industries, intending to preserve the wall's stability and the chemical and compositional properties of the underlying rock. In situ minerals are often coated in other material deposits, such as dust or slurry in blast holes. To analyse the rock materials beneath, its surface must be exposed by removal of the surface layer. The ablation depth per pulse and ablation efficiency of the slurry were determined using femtosecond laser pulses. Then, the ablation of rocks of economic interest in Australia, including banded iron, limonite, goethite, shale, and hematite, was studied to establish their ablation thresholds and rates. Any damage induced by the laser was investigated by optical microscopy, optical profilometry, colourimetry, VIS/NIR spectroscopy and Fourier Transform Infrared spectroscopy (FTIR).

We investigated the effect of femtosecond (fs) laser ablation of enamel and dentin for different pulse wavelengths: infrared (1030 nm), green (515 nm), and ultra-violet (343 nm) and for different pulse separations to determine the optimal irradiation conditions for the precise removal of dental hard tissues with the absence of structural and compositional damage. The ablation rates and efficiencies were established for all three laser wavelengths for both enamel and dentin at room temperature without using any irrigation or cooling system, and the surfaces were assessed with optical and scanning electron microscopy, optical profilometry, and Raman spectroscopy. We demonstrated that 515 nm fs irradiation provides the highest rate and efficiency for ablation, followed by infrared. Finally, we explored the temperature variations inside the dental pulp during the laser procedures for all three wavelengths and showed that the maximum increase at the optimum conditions for both infrared and green irradiations was 5.5 °C, within the acceptable limit of temperature increase during conventional dental treatments. Ultra-violet irradiation significantly increased the internal temperature of the teeth, well above the acceptable limit, and caused severe damage to tooth structures. Thus, ultra-violet is not a compatible laser wavelength for femtosecond teeth ablation.

We investigated the effect of femtosecond (fs) laser ablation of enamel and dentin for different pulse wavelengths: infrared (1030 nm), green (515 nm), and ultra-violet (343 nm) and for different pulse separations to determine the optimal irradiation conditions for the precise removal of dental hard tissues with the absence of structural and compositional damage. The ablation rates and efficiencies were established for all three laser wavelengths for both enamel and dentin at room temperature without using any irrigation or cooling system, and the surfaces were assessed with optical and scanning electron microscopy, optical profilometry, and Raman spectroscopy. We demonstrated that 515 nm fs irradiation provides the highest rate and efficiency for ablation, followed by infrared. Finally, we explored the temperature variations inside the dental pulp during the laser procedures for all three wavelengths and showed that the maximum increase at the optimum conditions for both infrared and green irradiations was 5.5˚C, within the acceptable limit of temperature increase during conventional dental treatments. Ultra-violet irradiation significantly increased the internal temperature of the teeth, well above the acceptable limit, and caused severe damage to tooth structures. Thus, ultra-violet is not a compatible laser wavelength for femtosecond teeth ablation.