Vulnerable newborn types: Analysis of population-based registries for 165 million births in 23 countries, 2000-2021.

OBJECTIVE: To examine the prevalence of novel newborn types among 165 million live births in 23 countries from 2000 to 2021. DESIGN: Population-based, multi-country analysis. SETTING: National data systems in 23 middle- and high-income countries. POPULATION: Liveborn infants. METHODS: Country teams with high-quality data were invited to be part of the Vulnerable Newborn Measurement Collaboration. We classified live births by six newborn types based on gestational age information (preterm 90th centile) for gestational age, according to INTERGROWTH-21st standards. We considered small newborn types of any combination of preterm or SGA, and term + LGA was considered large. Time trends were analysed using 3-year moving averages for small and large types. MAIN OUTCOME MEASURES: Prevalence of six newborn types. RESULTS: We analysed 165 017 419 live births and the median prevalence of small types was 11.7% - highest in Malaysia (26%) and Qatar (15.7%). Overall, 18.1% of newborns were large (term + LGA) and was highest in Estonia 28.8% and Denmark 25.9%. Time trends of small and large infants were relatively stable in most countries. CONCLUSIONS: The distribution of newborn types varies across the 23 middle- and high-income countries. Small newborn types were highest in west Asian countries and large types were highest in Europe. To better understand the global patterns of these novel newborn types, more information is needed, especially from low- and middle-income countries

Improved laser glass cutting by spatio-temporal control of energy deposition using bursts of femtosecond pulses

We demonstrate the advantage of combining non-diffractive beam shapes and femtosecond bursts for volume laser processing of transparent materials. By redistribution of the single laser pulse energy into several sub-pulses with 25 ns time delay, the energy deposition in the material can be enhanced significantly. Our combined experimental and theoretical analysis shows that in burst-mode detrimental defocusing by the laser generated plasma is reduced, and the non-diffractive beam shape prevails. At the same time, heat accumulation during the interaction with the burst leads to temperatures high enough to induce material melting and even in-volume cracks. In an exemplary case study, we demonstrate that the formation of these cracks can be controlled to allow high-speed and high-quality glass cutting

Material Processing by fs Laser Pulse Trains: Experiments vs. Simulations

The use of femtosecond (fs) trains of pulse is now well established as an efficient technique to modify dielectric materials. Through numerous experimental parameters, it is possible to adjust the amount of deposited energy into the material with a great accuracy. When an intense fs laser pulse is focused inside a dielectric material, here soda-lime glass, electrons get promoted from the valence band (VB) to the conduction band (CB) by photo-ionization processes. After the fs pulse interaction, electrons in the CB transfer their energy to the lattice through collisional processes, and heat diffusion towards the surrounding cold matter of the focal point sets in. Due to the low heat diffusion coefficient (a few microseconds for micron-size volume), and by using a few hundreds kilohertz repetition rate (RR), one can achieve pulse-to-pulse accumulation of temperature. For sufficiently large number of pulses, it is possible to exceed the annealing temperature, and the dielectric material gets modified permanently. Our approach to simulate this phenomenon is based on the separation of the different timescales of the key physical processes. To this end, the laser pulse propagation is simulated by a paraxial Forward Maxwell code taking into account key nonlinear effects, in order to compute the single pulse energy deposition in the material. Thermal diffusion is taken into account by the heat equation, where we use the (repeated) single pulse energy deposition as heat source. Finally, reaching the annealing temperature is used as a threshold to get the dimensions of the permanent modification of the matter. Simulations and experiments were performed in soda-lime glass for a train of 300 fs pulses with an incident energy of 1.3 µJ per pulse. The laser beam, with a wavelength centered around 1030 nm, was focused into the glass bulk by a 10× objective. The theoretically predicted dimensions of the glass transition temperature zone are confronted with the dimensions of the experimental modifications of the glass. We note a threshold-like behavior for the onset of measurable modifications between 100 and 200 kHz, in the experiments as well as in the simulation results. The experimental dimensions are well reproduced by our model, despite a slight deviation in the predicted length for 200 and 300 kHz. We attribute this discrepancy to changes in the propagation dynamics due to successive material modification which is not (yet) taken account in this work

Femtosecond laser cutting of glass by controlled fracture propagation

We present the use of a compact femtosecond laser with 300-fs pulse duration and pulse energy on the order of 10s of µJ for the cutting of glass by controlled fracture propagation

Modeling dielectric material modifications by trains of fs laser pulses

We show that by taking into account nonlinear pulse propagation effects, heat diffusion, and heat accumulation, it is possible to explain size and shape of dielectric material modifications induced by trains of fs laser pulses

Effects of burst mode on transparent materials processing

We investigated the effect of burstmode with nanosecond (ns) time delay between subpulses on sodalime glass volume machining. We observed in tight focusing configuration that the use of burstmode with ns time delay between subpulses does not increase the absorption efficiency and does not bring a significant effect on the heat affected zone diameter with respect to single pulse mode. On the contrary in loose focusing configuration the use of burst mode allows increasing the aspect ratio of the heat affected zone without extra energy absorption. This effect is highly interesting for filamentation glass cutting applications