Ultrafast laser welding of silicon

While ultrafast laser welding is an appealing technique for bonding transparent workpieces, it is not applicable for joining silicon samples due to nonlinear propagation effects which dramatically diminishes the possible energy deposition at the interface. We demonstrate that these limitations can be circumvented by local absorption enhancement at the interface thanks to metallic nanolayer deposition. By combining the resulting exalted absorption with filament relocation during ultrafast laser irradiation, silicon samples can be efficiently joined. Shear joining strengths >4 MPa are obtained for 21-nm gold nanolayers without laser-induced alteration of the transmittance. Such remarkable strength values hold promises for applications in microelectronics, optics, and astronomy.Comment: 8 pages, 5 figure

Taming ultrafast laser filaments for optimized semiconductor–metal welding

Ultrafast laser welding is a fast, clean, and contactless technique for joining a broad range of materials. Nevertheless, this technique cannot be applied for bonding semiconductors and metals. By investigating the nonlinear propagation of picosecond laser pulses in silicon, it is elucidated how the evolution of filaments during propagation prevents the energy deposition at the semiconductor–metal interface. While the restrictions imposed by nonlinear propagation effects in semiconductors usually inhibit countless applications, the possibility to perform semiconductor–metal ultrafast laser welding is demonstrated. This technique relies on the determination and the precompensation of the nonlinear focal shift for relocating filaments and thus optimizing the energy deposition at the interface between the materials. The resulting welds show remarkable shear joining strengths (up to 2.2 MPa) compatible with applications in microelectronics. Material analyses shed light on the physical mechanisms involved during the interaction

Three-dimensional writing inside silicon using a 2-µm picosecond fiber laser

International audienc

Lot-to-lot consistency of a tetravalent dengue vaccine in healthy adults in Australia: a randomised study

Background: The recombinant yellow fever-17D-dengue virus, live, attenuated, tetravalent dengue vac-cine (CYD-TDV) has undergone extensive clinical trials. Here safety and consistency of immunogenicityof phase III manufacturing lots of CYD-TDV were evaluated and compared with a phase II lot and placeboin a dengue-naïve population.Methods: Healthy 18–60 year-olds were randomly assigned in a 3:3:3:3:1 ratio to receive three sub-cutaneous doses of either CYD-TDV from any one of three phase III lots or a phase II lot, or placebo,respectively in a 0, 6, 12 month dosing schedule. Neutralising antibody geometric mean titres (PRNT50GMTs) for each of the four dengue serotypes were compared in sera collected 28 days after the thirdvaccination—equivalence among lots was demonstrated if the lower and upper limits of the two-sided95% CIs of the GMT ratio were ≥0.5 and ≤2.0, respectively.Results: 712 participants received vaccine or placebo and 614 (86%) completed the study; 17 (2.4%) par-ticipants withdrew after adverse events. Equivalence of phase III lots was demonstrated for 11 of 12pairwise comparisons. One of three comparisons for serotype 2 was not statistically equivalent. GMTsfor serotype 2 in phase III lots were close to each other (65.9, 44.1 and 58.1, respectively).Conclusions: Phase III lots can be produced in a consistent manner with predictable immune responseand acceptable safety profile similar to previously characterised phase II lots. The phase III lots maybe considered as not clinically different as statistical equivalence was shown for serotypes 1, 3 and 4across the phase III lots. For serotype 2, although equivalence was not shown between two lots, the GMTsobserved in the phase III lots were consistently higher than those for the phase II lot. As such, in our view,biological equivalence for all serotypes was demonstrated.Joseph Torresi, Leon G. Heron, Ming Qiao, Joanne Marjason, Laurent Chambonneau, Alain Bouckenooghe, Mark Boaz, Diane van der Vliet, Derek Wallace, Yanee Hutagalung, Michael D. Nissen, Peter C. Richmon

PLoS One

OBJECTIVE: To evaluate the association of rainy season with overall dengue disease incidence and with the efficacy of the Sanofi Pasteur recombinant, live, attenuated, tetravalent vaccine (CYD-TDV) in two randomized, controlled multicenter phase III clinical trials in Asia and Latin America. METHODS: Rainy seasons were defined for each study site using climatological information from the World Meteorological Organization. The dengue attack rate in the placebo group for each study month was calculated as the number of symptomatic, virologically-confirmed dengue events in a given month divided by the number of participants at risk in the same month. Time-dependent Cox proportional hazard models were used to test whether rainy season was associated with dengue disease and whether it modified vaccine efficacy in each of the two trials and in both of the trials combined. FINDINGS: Rainy season, country, and age were all significantly associated with dengue disease in both studies. Vaccine efficacy did not change during the rainy season in any of the analyses. CONCLUSIONS: Although dengue transmission and exposure are expected to increase during the rainy season, our results indicate that CYD-TDV vaccine efficacy remains constant throughout the year in endemic regions

Study of laser-induced damage on the exit surface of silica components in the nanosecond regime in a multiple wavelengths configuration

Cette thèse porte sur l'endommagement laser à la surface de composants optiques en silice amorphe en régime nanoseconde. Ce phénomène est une modification irréversible du matériau. Dans le régime nanoseconde, l'endommagement laser de la silice est étroitement corrélé à la présence de défauts précurseurs qui sont une conséquence de la synthèse et du polissage des composants. Cette thèse propose des investigations sur l'endommagement laser par plusieurs longueurs d'onde simultanément. Afin de mieux appréhender ce phénomène dans ces conditions d'irradiation, trois études sont conduites. La première porte sur la phase d'amorçage des dommages. Les résultats expérimentaux obtenus dans les cas mono-longueur d'onde permettent de mettre en avant un couplage dans le cas multi-longueurs d'onde. Une comparaison de ces résultats avec un modèle théorique développé au cours de cette thèse permet d'améliorer la compréhension des processus fondamentaux liés à cette phase d'endommagement. Puis, des caractérisations morphologiques post mortem couplées à une métrologie précise des faisceaux laser permettent d'établir la nature ainsi que la chronologie des mécanismes conduisant à la formation des dommages. Le scénario théorique proposé est validé à travers différentes expériences. En dernier lieu, nous étudions la phase de croissance des dommages dans les cas mono et multi-longueurs d'onde. Une fois de plus, cette dernière configuration met en lumière un couplage entre les longueurs d'onde. Nous montrons la nécessité de prendre en compte les caractéristiques spatiales des faisceaux laser lors d'une session de croissance des dommages.In this thesis, laser-induced damage phenomenon on the surface of fused silica components is investigated in the nanosecond regime. This phenomenon consists in an irreversible modification of the material. In the nanosecond regime, laser damage is tightly correlated to the presence of non-detectable precursor defects which are a consequence of the synthesis and the polishing of the components. In this thesis, we investigate laser damage in a multiple wavelengths configuration. In order to better understand this phenomenon in these conditions of irradiation, three studies are conducted. The first one focuses on damage initiation. The results obtained in the single wavelength configurations highlight a coupling in the multiple wavelengths one. A comparison between the experiments and a model developed during this thesis enables us to improve the knowledge of the fundamental processes involved during this damage phase. Then, we show that post mortem characterizations of damage morphology coupled to an accurate metrology allow us to understand both the nature and also the chronology of the physical mechanisms involved during damage formation. The proposed theoretical scenario is confirmed through various experiments. Finally, we study damage growth in both the single and the multiple wavelengths cases. Once again, this last configuration highlights a coupling between the wavelengths. We show the necessity to account for the spatial characteristics of the laser beams during a growth session

Quantitative-phase microscopy of nanosecond laser-induced micro-modifications inside silicon

International audienceLaser-induced permanent modification inside silicon has been recently demonstrated by using tightly focused nanosecond sources at a 1550 nm wavelength. We have developed a quantitative-phase microscope operating in the near-infrared domain to characterize the laser-induced modifications deep into silicon. By varying the number of applied laser pulses and the energy, we observe porous and densified regions in the focal region. The observed changes are associated with refractive index variations jΔnj exceeding 10 −3 , enough to envision the laser writing of optical functionalities inside silicon